A compound page collects the refcount in the head page, while leaving the refcount of each tail page at zero. Therefore, when debugging a problem that involves compound pages, it's best to have diagnostics that reflect that situation. However, dump_page() is oblivious to these points.

Change dump_page() as follows:

1) For tail pages, print relevant head page information: refcount, in particular. But only do this if the page is not corrupted so badly that the pointer to the head page is all wrong.

2) Do a separate check to catch any (rare) cases of the tail page's refcount being non-zero, and issue a separate, clear pr_warn() if that ever happens.

Suggested-by: Matthew Wilcox willy@infradead.org Suggested-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/debug.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c index ecccd9f17801..f074077eee11 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -42,6 +42,33 @@ const struct trace_print_flags vmaflag_names[] = { {0, NULL} };

+static void __dump_tail_page(struct page *page, int mapcount) +{ + struct page *head = compound_head(page); + + if ((page < head) || (page >= head + MAX_ORDER_NR_PAGES)) { + /* + * Page is hopelessly corrupted, so limit any reporting to + * information about the page itself. Do not attempt to look at + * the head page. + */ + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " + "index:%#lx (corrupted tail page case)\n", + page, page_ref_count(page), mapcount, page->mapping, + page_to_pgoff(page)); + } else { + pr_warn("page:%px compound refcount:%d mapcount:%d mapping:%px " + "index:%#lx compound_mapcount:%d\n", + page, page_ref_count(head), mapcount, head->mapping, + page_to_pgoff(head), compound_mapcount(page)); + } + + if (page_ref_count(page) != 0) { + pr_warn("page:%px PROBLEM: non-zero refcount (==%d) on this " + "tail page\n", page, page_ref_count(page)); + } +} + void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; @@ -75,12 +102,8 @@ void __dump_page(struct page *page, const char *reason) */ mapcount = PageSlab(page) ? 0 : page_mapcount(page);

- if (PageCompound(page)) - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount: %d\n", - page, page_ref_count(page), mapcount, - page->mapping, page_to_pgoff(page), - compound_mapcount(page)); + if (PageTail(page)) + __dump_tail_page(page, mapcount); else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount,

A subsequent patch requires access to gup flags, so pass the flags argument through to the __gup_device_* functions.

Also placate checkpatch.pl by shortening a nearby line.

Reviewed-by: Jan Kara jack@suse.cz Reviewed-by: Jérôme Glisse jglisse@redhat.com Reviewed-by: Ira Weiny ira.weiny@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/gup.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c index b699500da077..9e117998274c 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1963,7 +1963,8 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE) static int __gup_device_huge(unsigned long pfn, unsigned long addr, - unsigned long end, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { int nr_start = *nr; struct dev_pagemap *pgmap = NULL; @@ -1989,13 +1990,14 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr, }

static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, - unsigned long end, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { unsigned long fault_pfn; int nr_start = *nr;

fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); - if (!__gup_device_huge(fault_pfn, addr, end, pages, nr)) + if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr)) return 0;

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { @@ -2006,13 +2008,14 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, }

static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, - unsigned long end, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { unsigned long fault_pfn; int nr_start = *nr;

fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); - if (!__gup_device_huge(fault_pfn, addr, end, pages, nr)) + if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr)) return 0;

if (unlikely(pud_val(orig) != pud_val(*pudp))) { @@ -2023,14 +2026,16 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, } #else static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, - unsigned long end, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { BUILD_BUG(); return 0; }

static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr, - unsigned long end, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { BUILD_BUG(); return 0; @@ -2146,7 +2151,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, if (pmd_devmap(orig)) { if (unlikely(flags & FOLL_LONGTERM)) return 0; - return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr); + return __gup_device_huge_pmd(orig, pmdp, addr, end, flags, + pages, nr); }

page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); @@ -2167,7 +2173,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, }

static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, - unsigned long end, unsigned int flags, struct page **pages, int *nr) + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { struct page *head, *page; int refs; @@ -2178,7 +2185,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, if (pud_devmap(orig)) { if (unlikely(flags & FOLL_LONGTERM)) return 0; - return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr); + return __gup_device_huge_pud(orig, pudp, addr, end, flags, + pages, nr); }

page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);

In preparation for an upcoming patch, send gup flags args to two more routines: put_compound_head(), and undo_dev_pagemap().

Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/gup.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c index 9e117998274c..e5f75e886663 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1870,6 +1870,7 @@ static inline pte_t gup_get_pte(pte_t *ptep) #endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */

static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start, + unsigned int flags, struct page **pages) { while ((*nr) - nr_start) { @@ -1909,7 +1910,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

pgmap = get_dev_pagemap(pte_pfn(pte), pgmap); if (unlikely(!pgmap)) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); goto pte_unmap; } } else if (pte_special(pte)) @@ -1974,7 +1975,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,

pgmap = get_dev_pagemap(pfn, pgmap); if (unlikely(!pgmap)) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } SetPageReferenced(page); @@ -2001,7 +2002,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0;

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } return 1; @@ -2019,7 +2020,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0;

if (unlikely(pud_val(orig) != pud_val(*pudp))) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } return 1; @@ -2053,7 +2054,7 @@ static int record_subpages(struct page *page, unsigned long addr, return nr; }

-static void put_compound_head(struct page *page, int refs) +static void put_compound_head(struct page *page, int refs, unsigned int flags) { VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); /* @@ -2103,7 +2104,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, return 0;

if (unlikely(pte_val(pte) != pte_val(*ptep))) { - put_compound_head(head, refs); + put_compound_head(head, refs, flags); return 0; }

@@ -2163,7 +2164,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0;

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { - put_compound_head(head, refs); + put_compound_head(head, refs, flags); return 0; }

@@ -2197,7 +2198,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0;

if (unlikely(pud_val(orig) != pud_val(*pudp))) { - put_compound_head(head, refs); + put_compound_head(head, refs, flags); return 0; }

@@ -2226,7 +2227,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, return 0;

if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { - put_compound_head(head, refs); + put_compound_head(head, refs, flags); return 0; }

Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details.

As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page().

Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.)

The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use".

Pages that have been pinned via FOLL_PIN are identifiable via a new function call:

bool page_maybe_dma_pinned(struct page *page);

What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4].

This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().

[1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages

Reviewed-by: Jan Kara jack@suse.cz Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Suggested-by: Jan Kara jack@suse.cz Suggested-by: Jérôme Glisse jglisse@redhat.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- Documentation/core-api/pin_user_pages.rst | 6 +- include/linux/mm.h | 82 +++++-- mm/gup.c | 254 +++++++++++++++++----- mm/huge_memory.c | 29 ++- mm/hugetlb.c | 54 +++-- 5 files changed, 334 insertions(+), 91 deletions(-)

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index 1d490155ecd7..9829345428f8 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -173,8 +173,8 @@ CASE 4: Pinning for struct page manipulation only ------------------------------------------------- Here, normal GUP calls are sufficient, so neither flag needs to be set.

-page_dma_pinned(): the whole point of pinning -============================================= +page_maybe_dma_pinned(): the whole point of pinning +===================================================

The whole point of marking pages as "DMA-pinned" or "gup-pinned" is to be able to query, "is this page DMA-pinned?" That allows code such as page_mkclean() @@ -186,7 +186,7 @@ and debates (see the References at the end of this document). It's a TODO item here: fill in the details once that's worked out. Meanwhile, it's safe to say that having this available: ::

- static inline bool page_dma_pinned(struct page *page) + static inline bool page_maybe_dma_pinned(struct page *page)

...is a prerequisite to solving the long-running gup+DMA problem.

diff --git a/include/linux/mm.h b/include/linux/mm.h index 52269e56c514..8d4f9f4094f4 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1001,6 +1001,8 @@ static inline void get_page(struct page *page) page_ref_inc(page); }

+bool __must_check try_grab_page(struct page *page, unsigned int flags); + static inline __must_check bool try_get_page(struct page *page) { page = compound_head(page); @@ -1029,29 +1031,79 @@ static inline void put_page(struct page *page) __put_page(page); }

-/** - * unpin_user_page() - release a gup-pinned page - * @page: pointer to page to be released +/* + * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overload + * the page's refcount so that two separate items are tracked: the original page + * reference count, and also a new count of how many pin_user_pages() calls were + * made against the page. ("gup-pinned" is another term for the latter). + * + * With this scheme, pin_user_pages() becomes special: such pages are marked as + * distinct from normal pages. As such, the unpin_user_page() call (and its + * variants) must be used in order to release gup-pinned pages. + * + * Choice of value: + * + * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference + * counts with respect to pin_user_pages() and unpin_user_page() becomes + * simpler, due to the fact that adding an even power of two to the page + * refcount has the effect of using only the upper N bits, for the code that + * counts up using the bias value. This means that the lower bits are left for + * the exclusive use of the original code that increments and decrements by one + * (or at least, by much smaller values than the bias value). * - * Pages that were pinned via pin_user_pages*() must be released via either - * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so - * that eventually such pages can be separately tracked and uniquely handled. In - * particular, interactions with RDMA and filesystems need special handling. + * Of course, once the lower bits overflow into the upper bits (and this is + * OK, because subtraction recovers the original values), then visual inspection + * no longer suffices to directly view the separate counts. However, for normal + * applications that don't have huge page reference counts, this won't be an + * issue. * - * unpin_user_page() and put_page() are not interchangeable, despite this early - * implementation that makes them look the same. unpin_user_page() calls must - * be perfectly matched up with pin*() calls. + * Locking: the lockless algorithm described in page_cache_get_speculative() + * and page_cache_gup_pin_speculative() provides safe operation for + * get_user_pages and page_mkclean and other calls that race to set up page + * table entries. */ -static inline void unpin_user_page(struct page *page) -{ - put_page(page); -} +#define GUP_PIN_COUNTING_BIAS (1U << 10)

+void unpin_user_page(struct page *page); void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages, bool make_dirty); - void unpin_user_pages(struct page **pages, unsigned long npages);

+/** + * page_maybe_dma_pinned() - report if a page is pinned for DMA. + * + * This function checks if a page has been pinned via a call to + * pin_user_pages*(). + * + * For non-huge pages, the return value is partially fuzzy: false is not fuzzy, + * because it means "definitely not pinned for DMA", but true means "probably + * pinned for DMA, but possibly a false positive due to having at least + * GUP_PIN_COUNTING_BIAS worth of normal page references". + * + * False positives are OK, because: a) it's unlikely for a page to get that many + * refcounts, and b) all the callers of this routine are expected to be able to + * deal gracefully with a false positive. + * + * For more information, please see Documentation/vm/pin_user_pages.rst. + * + * @page: pointer to page to be queried. + * @Return: True, if it is likely that the page has been "dma-pinned". + * False, if the page is definitely not dma-pinned. + */ +static inline bool page_maybe_dma_pinned(struct page *page) +{ + /* + * page_ref_count() is signed. If that refcount overflows, then + * page_ref_count() returns a negative value, and callers will avoid + * further incrementing the refcount. + * + * Here, for that overflow case, use the signed bit to count a little + * bit higher via unsigned math, and thus still get an accurate result. + */ + return ((unsigned int)page_ref_count(compound_head(page))) >= + GUP_PIN_COUNTING_BIAS; +} + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif diff --git a/mm/gup.c b/mm/gup.c index c8affbea2019..a2356482e1ea 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -44,6 +44,135 @@ static inline struct page *try_get_compound_head(struct page *page, int refs) return head; }

+/* + * try_grab_compound_head() - attempt to elevate a page's refcount, by a + * flags-dependent amount. + * + * "grab" names in this file mean, "look at flags to decide whether to use + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount. + * + * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the + * same time. (That's true throughout the get_user_pages*() and + * pin_user_pages*() APIs.) Cases: + * + * FOLL_GET: page's refcount will be incremented by 1. + * FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS. + * + * Return: head page (with refcount appropriately incremented) for success, or + * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's + * considered failure, and furthermore, a likely bug in the caller, so a warning + * is also emitted. + */ +static __maybe_unused struct page *try_grab_compound_head(struct page *page, + int refs, + unsigned int flags) +{ + if (flags & FOLL_GET) + return try_get_compound_head(page, refs); + else if (flags & FOLL_PIN) { + refs *= GUP_PIN_COUNTING_BIAS; + return try_get_compound_head(page, refs); + } + + WARN_ON_ONCE(1); + return NULL; +} + +/** + * try_grab_page() - elevate a page's refcount by a flag-dependent amount + * + * This might not do anything at all, depending on the flags argument. + * + * "grab" names in this file mean, "look at flags to decide whether to use + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount. + * + * @page: pointer to page to be grabbed + * @flags: gup flags: these are the FOLL_* flag values. + * + * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same + * time. Cases: + * + * FOLL_GET: page's refcount will be incremented by 1. + * FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS. + * + * Return: true for success, or if no action was required (if neither FOLL_PIN + * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or + * FOLL_PIN was set, but the page could not be grabbed. + */ +bool __must_check try_grab_page(struct page *page, unsigned int flags) +{ + WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN)); + + if (flags & FOLL_GET) + return try_get_page(page); + else if (flags & FOLL_PIN) { + page = compound_head(page); + + if (WARN_ON_ONCE(page_ref_count(page) <= 0)) + return false; + + page_ref_add(page, GUP_PIN_COUNTING_BIAS); + } + + return true; +} + +#ifdef CONFIG_DEV_PAGEMAP_OPS +static bool __unpin_devmap_managed_user_page(struct page *page) +{ + int count; + + if (!page_is_devmap_managed(page)) + return false; + + count = page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS); + + /* + * devmap page refcounts are 1-based, rather than 0-based: if + * refcount is 1, then the page is free and the refcount is + * stable because nobody holds a reference on the page. + */ + if (count == 1) + free_devmap_managed_page(page); + else if (!count) + __put_page(page); + + return true; +} +#else +static bool __unpin_devmap_managed_user_page(struct page *page) +{ + return false; +} +#endif /* CONFIG_DEV_PAGEMAP_OPS */ + +/** + * unpin_user_page() - release a dma-pinned page + * @page: pointer to page to be released + * + * Pages that were pinned via pin_user_pages*() must be released via either + * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so + * that such pages can be separately tracked and uniquely handled. In + * particular, interactions with RDMA and filesystems need special handling. + */ +void unpin_user_page(struct page *page) +{ + page = compound_head(page); + + /* + * For devmap managed pages we need to catch refcount transition from + * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the + * page is free and we need to inform the device driver through + * callback. See include/linux/memremap.h and HMM for details. + */ + if (__unpin_devmap_managed_user_page(page)) + return; + + if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS)) + __put_page(page); +} +EXPORT_SYMBOL(unpin_user_page); + /** * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages * @pages: array of pages to be maybe marked dirty, and definitely released. @@ -230,10 +359,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, }

page = vm_normal_page(vma, address, pte); - if (!page && pte_devmap(pte) && (flags & FOLL_GET)) { + if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) { /* - * Only return device mapping pages in the FOLL_GET case since - * they are only valid while holding the pgmap reference. + * Only return device mapping pages in the FOLL_GET or FOLL_PIN + * case since they are only valid while holding the pgmap + * reference. */ *pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap); if (*pgmap) @@ -271,11 +401,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, goto retry; }

- if (flags & FOLL_GET) { - if (unlikely(!try_get_page(page))) { - page = ERR_PTR(-ENOMEM); - goto out; - } + /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */ + if (unlikely(!try_grab_page(page, flags))) { + page = ERR_PTR(-ENOMEM); + goto out; } if (flags & FOLL_TOUCH) { if ((flags & FOLL_WRITE) && @@ -537,7 +666,7 @@ static struct page *follow_page_mask(struct vm_area_struct *vma, /* make this handle hugepd */ page = follow_huge_addr(mm, address, flags & FOLL_WRITE); if (!IS_ERR(page)) { - BUG_ON(flags & FOLL_GET); + WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN)); return page; }

@@ -1675,6 +1804,15 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, { return 0; } + +static long __get_user_pages_remote(struct task_struct *tsk, + struct mm_struct *mm, + unsigned long start, unsigned long nr_pages, + unsigned int gup_flags, struct page **pages, + struct vm_area_struct **vmas, int *locked) +{ + return 0; +} #endif /* !CONFIG_MMU */

/* @@ -1877,7 +2015,10 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start, struct page *page = pages[--(*nr)];

ClearPageReferenced(page); - put_page(page); + if (flags & FOLL_PIN) + unpin_user_page(page); + else + put_page(page); } }

@@ -1919,7 +2060,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte);

- head = try_get_compound_head(page, 1); + head = try_grab_compound_head(page, 1, flags); if (!head) goto pte_unmap;

@@ -1980,7 +2121,10 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr, } SetPageReferenced(page); pages[*nr] = page; - get_page(page); + if (unlikely(!try_grab_page(page, flags))) { + undo_dev_pagemap(nr, nr_start, flags, pages); + return 0; + } (*nr)++; pfn++; } while (addr += PAGE_SIZE, addr != end); @@ -2056,6 +2200,9 @@ static int record_subpages(struct page *page, unsigned long addr,

static void put_compound_head(struct page *page, int refs, unsigned int flags) { + if (flags & FOLL_PIN) + refs *= GUP_PIN_COUNTING_BIAS; + VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); /* * Calling put_page() for each ref is unnecessarily slow. Only the last @@ -2099,7 +2246,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, page = head + ((addr & (sz-1)) >> PAGE_SHIFT); refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(head, refs); + head = try_grab_compound_head(head, refs, flags); if (!head) return 0;

@@ -2159,7 +2306,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pmd_page(orig), refs); + head = try_grab_compound_head(pmd_page(orig), refs, flags); if (!head) return 0;

@@ -2193,7 +2340,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pud_page(orig), refs); + head = try_grab_compound_head(pud_page(orig), refs, flags); if (!head) return 0;

@@ -2222,7 +2369,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pgd_page(orig), refs); + head = try_grab_compound_head(pgd_page(orig), refs, flags); if (!head) return 0;

@@ -2505,11 +2652,11 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,

/** * get_user_pages_fast() - pin user pages in memory - * @start: starting user address - * @nr_pages: number of pages from start to pin - * @gup_flags: flags modifying pin behaviour - * @pages: array that receives pointers to the pages pinned. - * Should be at least nr_pages long. + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying pin behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. * * Attempt to pin user pages in memory without taking mm->mmap_sem. * If not successful, it will fall back to taking the lock and @@ -2543,9 +2690,12 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast); /** * pin_user_pages_fast() - pin user pages in memory without taking locks * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API. So, - * this is identical to get_user_pages_fast(). + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See + * get_user_pages_fast() for documentation on the function arguments, because + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via unpin_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for further details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2553,21 +2703,24 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast); int pin_user_pages_fast(unsigned long start, int nr_pages, unsigned int gup_flags, struct page **pages) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages_fast(start, nr_pages, gup_flags, pages); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN; + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); } EXPORT_SYMBOL_GPL(pin_user_pages_fast);

/** * pin_user_pages_remote() - pin pages of a remote process (task != current) * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API. So, - * this is identical to get_user_pages_remote(). + * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See + * get_user_pages_remote() for documentation on the function arguments, because + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via unpin_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2577,22 +2730,24 @@ long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas, int *locked) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags, pages, - vmas, locked); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN; + return __get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags, + pages, vmas, locked); } EXPORT_SYMBOL(pin_user_pages_remote);

/** * pin_user_pages() - pin user pages in memory for use by other devices * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API. So, - * this is identical to get_user_pages(). + * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and + * FOLL_PIN is set. + * + * FOLL_PIN means that the pages must be released via unpin_user_page(). Please + * see Documentation/vm/pin_user_pages.rst for details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2601,11 +2756,12 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages(start, nr_pages, gup_flags, pages, vmas); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |= FOLL_PIN; + return __gup_longterm_locked(current, current->mm, start, nr_pages, + pages, vmas, gup_flags); } EXPORT_SYMBOL(pin_user_pages); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b08b199f9a11..580098e115bd 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -958,6 +958,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, */ WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");

+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + if (flags & FOLL_WRITE && !pmd_write(*pmd)) return NULL;

@@ -973,7 +978,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, * device mapped pages can only be returned if the * caller will manage the page reference count. */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST);

pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT; @@ -981,7 +986,8 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, if (!*pgmap) return ERR_PTR(-EFAULT); page = pfn_to_page(pfn); - get_page(page); + if (!try_grab_page(page, flags)) + page = ERR_PTR(-ENOMEM);

return page; } @@ -1101,6 +1107,11 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, if (flags & FOLL_WRITE && !pud_write(*pud)) return NULL;

+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + if (pud_present(*pud) && pud_devmap(*pud)) /* pass */; else @@ -1112,8 +1123,10 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, /* * device mapped pages can only be returned if the * caller will manage the page reference count. + * + * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here: */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST);

pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT; @@ -1121,7 +1134,8 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, if (!*pgmap) return ERR_PTR(-EFAULT); page = pfn_to_page(pfn); - get_page(page); + if (!try_grab_page(page, flags)) + page = ERR_PTR(-ENOMEM);

return page; } @@ -1497,8 +1511,13 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,

page = pmd_page(*pmd); VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); + + if (!try_grab_page(page, flags)) + return ERR_PTR(-ENOMEM); + if (flags & FOLL_TOUCH) touch_pmd(vma, addr, pmd, flags); + if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* * We don't mlock() pte-mapped THPs. This way we can avoid @@ -1535,8 +1554,6 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, skip_mlock: page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT; VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page); - if (flags & FOLL_GET) - get_page(page);

out: return page; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dd8737a94bec..ba1de6bc1402 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4375,19 +4375,6 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT; page = pte_page(huge_ptep_get(pte));

- /* - * Instead of doing 'try_get_page()' below in the same_page - * loop, just check the count once here. - */ - if (unlikely(page_count(page) <= 0)) { - if (pages) { - spin_unlock(ptl); - remainder = 0; - err = -ENOMEM; - break; - } - } - /* * If subpage information not requested, update counters * and skip the same_page loop below. @@ -4405,7 +4392,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, same_page: if (pages) { pages[i] = mem_map_offset(page, pfn_offset); - get_page(pages[i]); + /* + * try_grab_page() should always succeed here, because: + * a) we hold the ptl lock, and b) we've just checked + * that the huge page is present in the page tables. If + * the huge page is present, then the tail pages must + * also be present. The ptl prevents the head page and + * tail pages from being rearranged in any way. So this + * page must be available at this point, unless the page + * refcount overflowed: + */ + if (WARN_ON_ONCE(!try_grab_page(pages[i], flags))) { + spin_unlock(ptl); + remainder = 0; + err = -ENOMEM; + break; + } }

if (vmas) @@ -4965,6 +4967,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, struct page *page = NULL; spinlock_t *ptl; pte_t pte; + + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + retry: ptl = pmd_lockptr(mm, pmd); spin_lock(ptl); @@ -4977,8 +4985,18 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, pte = huge_ptep_get((pte_t *)pmd); if (pte_present(pte)) { page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); - if (flags & FOLL_GET) - get_page(page); + /* + * try_grab_page() should always succeed here, because: a) we + * hold the pmd (ptl) lock, and b) we've just checked that the + * huge pmd (head) page is present in the page tables. The ptl + * prevents the head page and tail pages from being rearranged + * in any way. So this page must be available at this point, + * unless the page refcount overflowed: + */ + if (WARN_ON_ONCE(!try_grab_page(page, flags))) { + page = NULL; + goto out; + } } else { if (is_hugetlb_entry_migration(pte)) { spin_unlock(ptl); @@ -4999,7 +5017,7 @@ struct page * __weak follow_huge_pud(struct mm_struct *mm, unsigned long address, pud_t *pud, int flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL;

return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); @@ -5008,7 +5026,7 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address, struct page * __weak follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL;

return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);

As part of pin_user_pages() and related API calls, pages are "dma-pinned". For the case of compound pages of order > 1, the per-page accounting of dma pins is accomplished via the 3rd struct page in the compound page. In order to support debugging of any pin_user_pages()- related problems, enhance dump_page() so as to report the pin count in that case.

Documentation/core-api/pin_user_pages.rst is also updated accordingly.

Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: John Hubbard jhubbard@nvidia.com --- Documentation/core-api/pin_user_pages.rst | 7 +++++ mm/debug.c | 34 +++++++++++++++++------ 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index 7e5dd8b1b3f2..24641f1a1eba 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -215,6 +215,13 @@ Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is because there is a noticeable performance drop in unpin_user_page(), when they are activated.

+Other diagnostics +================= + +dump_page() has been enhanced slightly, to handle these new counting fields, and +to better report on compound pages in general. Specifically, for compound pages +with order > 1, the exact (hpage_pinned_refcount) pincount is reported. + References ==========

diff --git a/mm/debug.c b/mm/debug.c index f074077eee11..e82c878c27df 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -57,10 +57,20 @@ static void __dump_tail_page(struct page *page, int mapcount) page, page_ref_count(page), mapcount, page->mapping, page_to_pgoff(page)); } else { - pr_warn("page:%px compound refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount:%d\n", - page, page_ref_count(head), mapcount, head->mapping, - page_to_pgoff(head), compound_mapcount(page)); + if (hpage_pincount_available(page)) + pr_warn("page:%px compound refcount:%d mapcount:%d " + "mapping:%px index:%#lx compound_mapcount:%d " + "compound_pincount:%d\n", + page, page_ref_count(head), mapcount, + head->mapping, page_to_pgoff(head), + compound_mapcount(page), + compound_pincount(page)); + else + pr_warn("page:%px compound refcount:%d mapcount:%d " + "mapping:%px index:%#lx compound_mapcount:%d\n", + page, page_ref_count(head), mapcount, + head->mapping, page_to_pgoff(head), + compound_mapcount(page)); }

if (page_ref_count(page) != 0) { @@ -104,10 +114,18 @@ void __dump_page(struct page *page, const char *reason)

if (PageTail(page)) __dump_tail_page(page, mapcount); - else - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", - page, page_ref_count(page), mapcount, - page->mapping, page_to_pgoff(page)); + else { + if (hpage_pincount_available(page)) + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " + "index:%#lx compound pincount: %d\n", + page, page_ref_count(page), mapcount, + page->mapping, page_to_pgoff(page), + compound_pincount(page)); + else + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " + "index:%#lx\n", page, page_ref_count(page), + mapcount, page->mapping, page_to_pgoff(page)); + } if (PageKsm(page)) type = "ksm "; else if (PageAnon(page))

Up until now, gup_benchmark supported testing of the following kernel functions:

* get_user_pages(): via the '-U' command line option * get_user_pages_longterm(): via the '-L' command line option * get_user_pages_fast(): as the default (no options required)

Add test coverage for the new corresponding pin_*() functions:

* pin_user_pages_fast(): via the '-a' command line option * pin_user_pages(): via the '-b' command line option

Also, add an option for clarity: '-u' for what is now (still) the default choice: get_user_pages_fast().

Also, for the commands that set FOLL_PIN, verify that the pages really are dma-pinned, via the new is_dma_pinned() routine. Those commands are:

PIN_FAST_BENCHMARK : calls pin_user_pages_fast() PIN_BENCHMARK : calls pin_user_pages()

In between the calls to pin_*() and unpin_user_pages(), check each page: if page_maybe_dma_pinned() returns false, then WARN and return.

Do this outside of the benchmark timestamps, so that it doesn't affect reported times.

Reviewed-by: Ira Weiny ira.weiny@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/gup_benchmark.c | 71 ++++++++++++++++++++-- tools/testing/selftests/vm/gup_benchmark.c | 15 ++++- 2 files changed, 80 insertions(+), 6 deletions(-)

diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c index 8dba38e79a9f..be690fa66a46 100644 --- a/mm/gup_benchmark.c +++ b/mm/gup_benchmark.c @@ -8,6 +8,8 @@ #define GUP_FAST_BENCHMARK _IOWR('g', 1, struct gup_benchmark) #define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) #define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark) +#define PIN_FAST_BENCHMARK _IOWR('g', 4, struct gup_benchmark) +#define PIN_BENCHMARK _IOWR('g', 5, struct gup_benchmark)

struct gup_benchmark { __u64 get_delta_usec; @@ -19,6 +21,48 @@ struct gup_benchmark { __u64 expansion[10]; /* For future use */ };

+static void put_back_pages(unsigned int cmd, struct page **pages, + unsigned long nr_pages) +{ + unsigned long i; + + switch (cmd) { + case GUP_FAST_BENCHMARK: + case GUP_LONGTERM_BENCHMARK: + case GUP_BENCHMARK: + for (i = 0; i < nr_pages; i++) + put_page(pages[i]); + break; + + case PIN_FAST_BENCHMARK: + case PIN_BENCHMARK: + unpin_user_pages(pages, nr_pages); + break; + } +} + +static void verify_dma_pinned(unsigned int cmd, struct page **pages, + unsigned long nr_pages) +{ + unsigned long i; + struct page *page; + + switch (cmd) { + case PIN_FAST_BENCHMARK: + case PIN_BENCHMARK: + for (i = 0; i < nr_pages; i++) { + page = pages[i]; + if (WARN(!page_maybe_dma_pinned(page), + "pages[%lu] is NOT dma-pinned\n", i)) { + + dump_page(page, "gup_benchmark failure"); + break; + } + } + break; + } +} + static int __gup_benchmark_ioctl(unsigned int cmd, struct gup_benchmark *gup) { @@ -66,6 +110,14 @@ static int __gup_benchmark_ioctl(unsigned int cmd, nr = get_user_pages(addr, nr, gup->flags, pages + i, NULL); break; + case PIN_FAST_BENCHMARK: + nr = pin_user_pages_fast(addr, nr, gup->flags, + pages + i); + break; + case PIN_BENCHMARK: + nr = pin_user_pages(addr, nr, gup->flags, pages + i, + NULL); + break; default: kvfree(pages); ret = -EINVAL; @@ -78,15 +130,22 @@ static int __gup_benchmark_ioctl(unsigned int cmd, } end_time = ktime_get();

+ /* Shifting the meaning of nr_pages: now it is actual number pinned: */ + nr_pages = i; + gup->get_delta_usec = ktime_us_delta(end_time, start_time); gup->size = addr - gup->addr;

+ /* + * Take an un-benchmark-timed moment to verify DMA pinned + * state: print a warning if any non-dma-pinned pages are found: + */ + verify_dma_pinned(cmd, pages, nr_pages); + start_time = ktime_get(); - for (i = 0; i < nr_pages; i++) { - if (!pages[i]) - break; - put_page(pages[i]); - } + + put_back_pages(cmd, pages, nr_pages); + end_time = ktime_get(); gup->put_delta_usec = ktime_us_delta(end_time, start_time);

@@ -105,6 +164,8 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd, case GUP_FAST_BENCHMARK: case GUP_LONGTERM_BENCHMARK: case GUP_BENCHMARK: + case PIN_FAST_BENCHMARK: + case PIN_BENCHMARK: break; default: return -EINVAL; diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c index 389327e9b30a..43b4dfe161a2 100644 --- a/tools/testing/selftests/vm/gup_benchmark.c +++ b/tools/testing/selftests/vm/gup_benchmark.c @@ -18,6 +18,10 @@ #define GUP_LONGTERM_BENCHMARK _IOWR('g', 2, struct gup_benchmark) #define GUP_BENCHMARK _IOWR('g', 3, struct gup_benchmark)

+/* Similar to above, but use FOLL_PIN instead of FOLL_GET. */ +#define PIN_FAST_BENCHMARK _IOWR('g', 4, struct gup_benchmark) +#define PIN_BENCHMARK _IOWR('g', 5, struct gup_benchmark) + /* Just the flags we need, copied from mm.h: */ #define FOLL_WRITE 0x01 /* check pte is writable */

@@ -40,8 +44,14 @@ int main(int argc, char **argv) char *file = "/dev/zero"; char *p;

- while ((opt = getopt(argc, argv, "m:r:n:f:tTLUwSH")) != -1) { + while ((opt = getopt(argc, argv, "m:r:n:f:abtTLUuwSH")) != -1) { switch (opt) { + case 'a': + cmd = PIN_FAST_BENCHMARK; + break; + case 'b': + cmd = PIN_BENCHMARK; + break; case 'm': size = atoi(optarg) * MB; break; @@ -63,6 +73,9 @@ int main(int argc, char **argv) case 'U': cmd = GUP_BENCHMARK; break; + case 'u': + cmd = GUP_FAST_BENCHMARK; + break; case 'w': write = 1; break;

On Thu, Feb 06, 2020 at 07:37:24PM -0800, John Hubbard wrote:

A compound page collects the refcount in the head page, while leaving the refcount of each tail page at zero. Therefore, when debugging a problem that involves compound pages, it's best to have diagnostics that reflect that situation. However, dump_page() is oblivious to these points.

Change dump_page() as follows:

1. For tail pages, print relevant head page information: refcount, in particular. But only do this if the page is not corrupted so badly that the pointer to the head page is all wrong.

2. Do a separate check to catch any (rare) cases of the tail page's refcount being non-zero, and issue a separate, clear pr_warn() if that ever happens.

Suggested-by: Matthew Wilcox willy@infradead.org Suggested-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com

---

mm/debug.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c index ecccd9f17801..f074077eee11 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -42,6 +42,33 @@ const struct trace_print_flags vmaflag_names[] = { {0, NULL} }; +static void __dump_tail_page(struct page *page, int mapcount) +{

• struct page *head = compound_head(page);
• if ((page < head) || (page >= head + MAX_ORDER_NR_PAGES)) {

• /*
  

•  * Page is hopelessly corrupted, so limit any reporting to
  

•  * information about the page itself. Do not attempt to look at
  

•  * the head page.
  

•  */
  

• pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
  

• 	"index:%#lx (corrupted tail page case)\n",
  

• 	page, page_ref_count(page), mapcount, page->mapping,
  

• 	page_to_pgoff(page));
  

• } else {

• pr_warn("page:%px compound refcount:%d mapcount:%d mapping:%px "
  

• 	"index:%#lx compound_mapcount:%d\n",
  

• 	page, page_ref_count(head), mapcount, head->mapping,
  

• 	page_to_pgoff(head), compound_mapcount(page));
  

• }
• if (page_ref_count(page) != 0) {

• pr_warn("page:%px PROBLEM: non-zero refcount (==%d) on this "
  

• 	"tail page\n", page, page_ref_count(page));
  

• }

+}

void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; @@ -75,12 +102,8 @@ void __dump_page(struct page *page, const char *reason) */ mapcount = PageSlab(page) ? 0 : page_mapcount(page);

• if (PageCompound(page))

• pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
  

• 	"index:%#lx compound_mapcount: %d\n",
  

• 	page, page_ref_count(page), mapcount,
  

• 	page->mapping, page_to_pgoff(page),
  

• 	compound_mapcount(page));
  

• if (PageTail(page))

• __dump_tail_page(page, mapcount);
  

  else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount,

A definite improvement, but I think we could do better. For example, you've changed PageCompound to PageTail here, whereas we really do want to dump some more information for PageHead pages than the plain vanilla order-0 page has. Another thing is that page_mapping() calls compound_head(), so if the page is corrupted, we're going to get a funky pointer dereference.

I spent a bit of time on this reimplementation ... what do you think?

- Print the mapping pointer using %p insted of %px. The actual value of the pointer can be read out of the raw page dump and using %p gives a chance to correlate it to earlier printk of the mapping pointer. - Add the order of the page for compound pages - Dump the raw head page as well as the raw page being dumped

diff --git a/mm/debug.c b/mm/debug.c index ecccd9f17801..0564d4cb8233 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -44,8 +44,10 @@ const struct trace_print_flags vmaflag_names[] = {

void __dump_page(struct page *page, const char *reason) { + struct page *head = compound_head(page); struct address_space *mapping; bool page_poisoned = PagePoisoned(page); + bool compound = PageCompound(page); /* * Accessing the pageblock without the zone lock. It could change to * "isolate" again in the meantime, but since we are just dumping the @@ -66,25 +68,32 @@ void __dump_page(struct page *page, const char *reason) goto hex_only; }

- mapping = page_mapping(page); + if (page < head || (page >= head + MAX_ORDER_NR_PAGES)) { + /* Corrupt page, cannot call page_mapping */ + mapping = page->mapping; + head = page; + compound = false; + } else { + mapping = page_mapping(page); + }

/* * Avoid VM_BUG_ON() in page_mapcount(). * page->_mapcount space in struct page is used by sl[aou]b pages to * encode own info. */ - mapcount = PageSlab(page) ? 0 : page_mapcount(page); + mapcount = PageSlab(head) ? 0 : page_mapcount(head);

- if (PageCompound(page)) - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount: %d\n", - page, page_ref_count(page), mapcount, + if (compound) + pr_warn("page:%px head:%px refcount:%d mapcount:%d mapping:%p " + "index:%#lx order:%u compound_mapcount: %d\n", + page, head, page_ref_count(page), mapcount, page->mapping, page_to_pgoff(page), - compound_mapcount(page)); + compound_order(head), compound_mapcount(page)); else - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", + pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n", page, page_ref_count(page), mapcount, - page->mapping, page_to_pgoff(page)); + mapping, page_to_pgoff(page)); if (PageKsm(page)) type = "ksm "; else if (PageAnon(page)) @@ -106,6 +115,10 @@ void __dump_page(struct page *page, const char *reason) print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32, sizeof(unsigned long), page, sizeof(struct page), false); + if (!page_poisoned && compound) + print_hex_dump(KERN_WARNING, "head: ", DUMP_PREFIX_NONE, 32, + sizeof(unsigned long), head, + sizeof(struct page), false);

if (reason) pr_warn("page dumped because: %s\n", reason);

On 2/10/20 2:16 AM, Jan Kara wrote:

On Thu 06-02-20 19:37:33, John Hubbard wrote:

...

@@ -2258,6 +2268,8 @@ static int record_subpages(struct page *page, unsigned long addr, static void put_compound_head(struct page *page, int refs, unsigned int flags) {

• int orig_refs = refs;
• if (flags & FOLL_PIN) { if (hpage_pincount_available(page)) hpage_pincount_sub(page, refs);

@@ -2273,6 +2285,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags) if (refs > 1) page_ref_sub(page, refs - 1); put_page(page);

• mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, orig_refs); }

Still not quite happy about this :) Now you update NR_FOLL_PIN_RELEASED even if 'flags' don't have FOLL_PIN set. You need to have the mod_node_page_state() inside the "if (flags & FOLL_PIN)" branch above...

							Honza

Arggh, yes that's true. Thanks for catching that, will fix in v6.

thanks,