[PATCH 2/2] mm/hugetlb: refactor subpage recording
From: Joao Martins <hidden>
Date: 2021-01-25 21:03:13
Also in:
lkml
Subsystem:
hugetlb subsystem, memory management, the rest · Maintainers:
Muchun Song, Oscar Salvador, Andrew Morton, Linus Torvalds
For a given hugepage backing a VA, there's a rather ineficient
loop which is solely responsible for storing subpages in the passed
pages/vmas array. For each subpage we check whether it's within
range or size of @pages and keep incrementing @pfn_offset and a couple
other variables per subpage iteration.
Simplify this logic and minimize ops per iteration to just
store the output page/vma. Instead of incrementing number of @refs
iteratively, we do it through a precalculation of @refs and having
only a tight loop for storing pinned subpages/vmas.
pinning consequently improves considerably, bringing us close to
{pin,get}_user_pages_fast:
- 16G with 1G huge page size
gup_test -f /mnt/huge/file -m 16384 -r 10 -L -S -n 512 -w
PIN_LONGTERM_BENCHMARK: ~11k us -> ~4400 us
PIN_FAST_BENCHMARK: ~3700 us
Signed-off-by: Joao Martins <redacted>
---
mm/hugetlb.c | 49 ++++++++++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 21 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 016addc8e413..1f7a95bc7c87 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c@@ -4789,6 +4789,20 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, goto out; } +static void record_subpages_vmas(struct page *page, struct vm_area_struct *vma, + int refs, struct page **pages, + struct vm_area_struct **vmas) +{ + int nr; + + for (nr = 0; nr < refs; nr++) { + if (likely(pages)) + pages[nr] = page++; + if (vmas) + vmas[nr] = vma; + } +} + long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, unsigned long *nr_pages,
@@ -4918,28 +4932,16 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, continue; } - refs = 0; + refs = min3(pages_per_huge_page(h) - pfn_offset, + (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder); -same_page: - if (pages) - pages[i] = mem_map_offset(page, pfn_offset); + if (pages || vmas) + record_subpages_vmas(mem_map_offset(page, pfn_offset), + vma, refs, + likely(pages) ? pages + i : NULL, + vmas ? vmas + i : NULL); - if (vmas) - vmas[i] = vma; - - vaddr += PAGE_SIZE; - ++pfn_offset; - --remainder; - ++i; - refs++; - if (vaddr < vma->vm_end && remainder && - pfn_offset < pages_per_huge_page(h)) { - /* - * We use pfn_offset to avoid touching the pageframes - * of this compound page. - */ - goto same_page; - } else if (pages) { + if (pages) { /* * try_grab_compound_head() should always succeed here, * because: a) we hold the ptl lock, and b) we've just
@@ -4950,7 +4952,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, * any way. So this page must be available at this * point, unless the page refcount overflowed: */ - if (WARN_ON_ONCE(!try_grab_compound_head(pages[i-1], + if (WARN_ON_ONCE(!try_grab_compound_head(pages[i], refs, flags))) { spin_unlock(ptl);
@@ -4959,6 +4961,11 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, break; } } + + vaddr += (refs << PAGE_SHIFT); + remainder -= refs; + i += refs; + spin_unlock(ptl); } *nr_pages = remainder;
--
2.17.1