6.16-stable review patch. If anyone has any objections, please let me know.
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From: Li Zhe lizhe.67@bytedance.com
commit a03db236aebfaeadf79396dbd570896b870bda01 upstream.
In the current implementation of longterm pin_user_pages(), we invoke collect_longterm_unpinnable_folios(). This function iterates through the list to check whether each folio belongs to the "longterm_unpinnabled" category. The folios in this list essentially correspond to a contiguous region of userspace addresses, with each folio representing a physical address in increments of PAGESIZE.
If this userspace address range is mapped with large folio, we can optimize the performance of function collect_longterm_unpinnable_folios() by reducing the using of READ_ONCE() invoked in pofs_get_folio()->page_folio()->_compound_head().
Also, we can simplify the logic of collect_longterm_unpinnable_folios(). Instead of comparing with prev_folio after calling pofs_get_folio(), we can check whether the next page is within the same folio.
The performance test results, based on v6.15, obtained through the gup_test tool from the kernel source tree are as follows. We achieve an improvement of over 66% for large folio with pagesize=2M. For small folio, we have only observed a very slight degradation in performance.
Without this patch:
[root@localhost ~] ./gup_test -HL -m 8192 -n 512 TAP version 13 1..1 # PIN_LONGTERM_BENCHMARK: Time: get:14391 put:10858 us# ok 1 ioctl status 0 # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 [root@localhost ~]# ./gup_test -LT -m 8192 -n 512 TAP version 13 1..1 # PIN_LONGTERM_BENCHMARK: Time: get:130538 put:31676 us# ok 1 ioctl status 0 # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
With this patch:
[root@localhost ~] ./gup_test -HL -m 8192 -n 512 TAP version 13 1..1 # PIN_LONGTERM_BENCHMARK: Time: get:4867 put:10516 us# ok 1 ioctl status 0 # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 [root@localhost ~]# ./gup_test -LT -m 8192 -n 512 TAP version 13 1..1 # PIN_LONGTERM_BENCHMARK: Time: get:131798 put:31328 us# ok 1 ioctl status 0 # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
[lizhe.67@bytedance.com: whitespace fix, per David] Link: https://lkml.kernel.org/r/20250606091917.91384-1-lizhe.67@bytedance.com Link: https://lkml.kernel.org/r/20250606023742.58344-1-lizhe.67@bytedance.com Signed-off-by: Li Zhe lizhe.67@bytedance.com Cc: David Hildenbrand david@redhat.com Cc: Dev Jain dev.jain@arm.com Cc: Jason Gunthorpe jgg@ziepe.ca Cc: John Hubbard jhubbard@nvidia.com Cc: Muchun Song muchun.song@linux.dev Cc: Peter Xu peterx@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/gup.c | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-)
--- a/mm/gup.c +++ b/mm/gup.c @@ -2300,6 +2300,31 @@ static void pofs_unpin(struct pages_or_f unpin_user_pages(pofs->pages, pofs->nr_entries); }
+static struct folio *pofs_next_folio(struct folio *folio, + struct pages_or_folios *pofs, long *index_ptr) +{ + long i = *index_ptr + 1; + + if (!pofs->has_folios && folio_test_large(folio)) { + const unsigned long start_pfn = folio_pfn(folio); + const unsigned long end_pfn = start_pfn + folio_nr_pages(folio); + + for (; i < pofs->nr_entries; i++) { + unsigned long pfn = page_to_pfn(pofs->pages[i]); + + /* Is this page part of this folio? */ + if (pfn < start_pfn || pfn >= end_pfn) + break; + } + } + + if (unlikely(i == pofs->nr_entries)) + return NULL; + *index_ptr = i; + + return pofs_get_folio(pofs, i); +} + /* * Returns the number of collected folios. Return value is always >= 0. */ @@ -2307,16 +2332,13 @@ static unsigned long collect_longterm_un struct list_head *movable_folio_list, struct pages_or_folios *pofs) { - unsigned long i, collected = 0; - struct folio *prev_folio = NULL; + unsigned long collected = 0; bool drain_allow = true; + struct folio *folio; + long i = 0;
- for (i = 0; i < pofs->nr_entries; i++) { - struct folio *folio = pofs_get_folio(pofs, i); - - if (folio == prev_folio) - continue; - prev_folio = folio; + for (folio = pofs_get_folio(pofs, i); folio; + folio = pofs_next_folio(folio, pofs, &i)) {
if (folio_is_longterm_pinnable(folio)) continue;