The patch titled
Subject: mm/gup: accelerate thp gup even for "pages != NULL"
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-accelerate-thp-gup-even-for-pages-=-null.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-accelerate-thp-gup-even-for-pages-=-null.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/gup: accelerate thp gup even for "pages != NULL"
Date: Wed, 28 Jun 2023 17:53:07 -0400
The acceleration of THP was done with ctx.page_mask, however it'll be
ignored if **pages is non-NULL.
The old optimization was introduced in 2013 in 240aadeedc4a ("mm:
accelerate mm_populate() treatment of THP pages"). It didn't explain why
we can't optimize the **pages non-NULL case. It's possible that at that
time the major goal was for mm_populate() which should be enough back
then.
Optimize thp for all cases, by properly looping over each subpage, doing
cache flushes, and boost refcounts / pincounts where needed in one go.
This can be verified using gup_test below:
# chrt -f 1 ./gup_test -m 512 -t -L -n 1024 -r 10
Before: 13992.50 ( +-8.75%)
After: 378.50 (+-69.62%)
Link: https://lkml.kernel.org/r/20230628215310.73782-6-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A . Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 44 insertions(+), 7 deletions(-)
--- a/mm/gup.c~mm-gup-accelerate-thp-gup-even-for-pages-=-null
+++ a/mm/gup.c
@@ -1247,16 +1247,53 @@ retry:
goto out;
}
next_page:
- if (pages) {
- pages[i] = page;
- flush_anon_page(vma, page, start);
- flush_dcache_page(page);
- ctx.page_mask = 0;
- }
-
page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
if (page_increm > nr_pages)
page_increm = nr_pages;
+
+ if (pages) {
+ struct page *subpage;
+ unsigned int j;
+
+ /*
+ * This must be a large folio (and doesn't need to
+ * be the whole folio; it can be part of it), do
+ * the refcount work for all the subpages too.
+ *
+ * NOTE: here the page may not be the head page
+ * e.g. when start addr is not thp-size aligned.
+ * try_grab_folio() should have taken care of tail
+ * pages.
+ */
+ if (page_increm > 1) {
+ struct folio *folio;
+
+ /*
+ * Since we already hold refcount on the
+ * large folio, this should never fail.
+ */
+ folio = try_grab_folio(page, page_increm - 1,
+ foll_flags);
+ if (WARN_ON_ONCE(!folio)) {
+ /*
+ * Release the 1st page ref if the
+ * folio is problematic, fail hard.
+ */
+ gup_put_folio(page_folio(page), 1,
+ foll_flags);
+ ret = -EFAULT;
+ goto out;
+ }
+ }
+
+ for (j = 0; j < page_increm; j++) {
+ subpage = nth_page(page, j);
+ pages[i + j] = subpage;
+ flush_anon_page(vma, subpage, start + j * PAGE_SIZE);
+ flush_dcache_page(subpage);
+ }
+ }
+
i += page_increm;
start += page_increm * PAGE_SIZE;
nr_pages -= page_increm;
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-hugetlb-handle-foll_dump-well-in-follow_page_mask.patch
mm-hugetlb-prepare-hugetlb_follow_page_mask-for-foll_pin.patch
mm-hugetlb-add-page_mask-for-hugetlb_follow_page_mask.patch
mm-gup-cleanup-next_page-handling.patch
mm-gup-accelerate-thp-gup-even-for-pages-=-null.patch
mm-gup-retire-follow_hugetlb_page.patch
selftests-mm-add-a-to-run_vmtestssh.patch
selftests-mm-add-gup-test-matrix-in-run_vmtestssh.patch
