For a given hugepage backing a VA, there's a rather ineficient
loop which is solely responsible for storing subpages in GUP
@pages/@vmas array. For each subpage we check whether it's within
range or size of @pages and keep increment @pfn_offset and a couple
other variables per subpage iteration.
Simplify this logic and minimize the cost of each iteration to just
store the output page/vma. Instead of incrementing number of @refs
iteratively, we do it through pre-calculation of @refs and only
with a tight loop for storing pinned subpages/vmas.
Additionally, retain existing behaviour with using mem_map_offset()
when recording the subpages for configurations that don't have a
contiguous mem_map.
pinning consequently improves bringing us close to
{pin,get}_user_pages_fast:
- 16G with 1G huge page size
gup_test -f /mnt/huge/file -m 16384 -r 30 -L -S -n 512 -w
PIN_LONGTERM_BENCHMARK: ~12.8k us -> ~5.8k us
PIN_FAST_BENCHMARK: ~3.7k us
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
---
mm/hugetlb.c | 49 ++++++++++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 21 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index becef936ec21..f3baabbda432 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] = mem_map_offset(page, nr);
+ 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
