On Mon 10-02-20 16:15:32, John Hubbard wrote:
Now that pages are "DMA-pinned" via pin_user_page*(), and unpinned via unpin_user_pages*(), we need some visibility into whether all of this is working correctly.
Add two new fields to /proc/vmstat:
nr_foll_pin_acquired nr_foll_pin_releasedThese are documented in Documentation/core-api/pin_user_pages.rst. They represent the number of pages (since boot time) that have been pinned ("nr_foll_pin_acquired") and unpinned ("nr_foll_pin_released"), via pin_user_pages*() and unpin_user_pages*().
In the absence of long-running DMA or RDMA operations that hold pages pinned, the above two fields will normally be equal to each other.
Also: update Documentation/core-api/pin_user_pages.rst, to remove an earlier (now confirmed untrue) claim about a performance problem with /proc/vmstat.
Also: updated Documentation/core-api/pin_user_pages.rst to rename the new /proc/vmstat entries, to the names listed here.
Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com
The patch looks good to me now. You can add:
Reviewed-by: Jan Kara jack@suse.cz
Honza
Documentation/core-api/pin_user_pages.rst | 33 +++++++++++++++++++---- include/linux/mmzone.h | 2 ++ mm/gup.c | 13 +++++++++ mm/vmstat.c | 2 ++ 4 files changed, 45 insertions(+), 5 deletions(-)
diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index 7e5dd8b1b3f2..5c8a5f89756b 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -208,12 +208,35 @@ has the following new calls to exercise the new pin*() wrapper functions: You can monitor how many total dma-pinned pages have been acquired and released since the system was booted, via two new /proc/vmstat entries: ::
- /proc/vmstat/nr_foll_pin_requested
- /proc/vmstat/nr_foll_pin_requested
- /proc/vmstat/nr_foll_pin_acquired
- /proc/vmstat/nr_foll_pin_released
-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. +Under normal conditions, these two values will be equal unless there are any +long-term [R]DMA pins in place, or during pin/unpin transitions.
+* nr_foll_pin_acquired: This is the number of logical pins that have been
- acquired since the system was powered on. For huge pages, the head page is
- pinned once for each page (head page and each tail page) within the huge page.
- This follows the same sort of behavior that get_user_pages() uses for huge
- pages: the head page is refcounted once for each tail or head page in the huge
- page, when get_user_pages() is applied to a huge page.
+* nr_foll_pin_released: The number of logical pins that have been released since
- the system was powered on. Note that pages are released (unpinned) on a
- PAGE_SIZE granularity, even if the original pin was applied to a huge page.
- Becaused of the pin count behavior described above in "nr_foll_pin_acquired",
- the accounting balances out, so that after doing this::
- pin_user_pages(huge_page);
- for (each page in huge_page)
unpin_user_page(page);+...the following is expected::
- nr_foll_pin_released == nr_foll_pin_acquired
+(...unless it was already out of balance due to a long-term RDMA pin being in +place.) References ========== diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 462f6873905a..4bca42eeb439 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -243,6 +243,8 @@ enum node_stat_item { NR_DIRTIED, /* page dirtyings since bootup */ NR_WRITTEN, /* page writings since bootup */ NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */
- NR_FOLL_PIN_ACQUIRED, /* via: pin_user_page(), gup flag: FOLL_PIN */
- NR_FOLL_PIN_RELEASED, /* pages returned via unpin_user_page() */ NR_VM_NODE_STAT_ITEMS
}; diff --git a/mm/gup.c b/mm/gup.c index 4d0d94405639..441f7a48f370 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -86,6 +86,8 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, if (flags & FOLL_GET) return try_get_compound_head(page, refs); else if (flags & FOLL_PIN) {
int orig_refs = refs;- /*
- When pinning a compound page of order > 1 (which is what
- hpage_pincount_available() checks for), use an exact count to
@@ -104,6 +106,9 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, if (hpage_pincount_available(page)) hpage_pincount_add(page, refs);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED,orig_refs);- return page; }
@@ -158,6 +163,8 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags) * once, so that the page really is pinned. */ page_ref_add(page, refs);
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);return true; @@ -178,6 +185,7 @@ static bool __unpin_devmap_managed_user_page(struct page *page) count = page_ref_sub_return(page, refs);
- mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); /*
- devmap page refcounts are 1-based, rather than 0-based: if
- refcount is 1, then the page is free and the refcount is
@@ -228,6 +236,8 @@ void unpin_user_page(struct page *page) if (page_ref_sub_and_test(page, refs)) __put_page(page);
- mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1);
} EXPORT_SYMBOL(unpin_user_page); @@ -2259,6 +2269,9 @@ 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) {
mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,refs);- if (hpage_pincount_available(page)) hpage_pincount_sub(page, refs); else
diff --git a/mm/vmstat.c b/mm/vmstat.c index 78d53378db99..c9c0d71f917f 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1168,6 +1168,8 @@ const char * const vmstat_text[] = { "nr_dirtied", "nr_written", "nr_kernel_misc_reclaimable",
- "nr_foll_pin_acquired",
- "nr_foll_pin_released",
/* enum writeback_stat_item counters */ "nr_dirty_threshold", -- 2.25.0