Commit 57edfcfd authored Jun 28, 2023 by Peter Xu Committed by Andrew Morton Aug 18, 2023

mm/gup: accelerate thp gup even for "pages != NULL"

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 240aadee ("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@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A . Shutemov <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent ffe1e786

mm/gup.c

+44 −7

Original line number	Diff line number	Diff line
		@@ -1282,16 +1282,53 @@ static long __get_user_pages(struct mm_struct *mm,
		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;