lkml.org 
[lkml]   [2021]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 2/4] mm/gup: decrement head page once for group of subpages
Date
Rather than decrementing the head page refcount one by one, we
walk the page array and checking which belong to the same
compound_head. Later on we decrement the calculated amount
of references in a single write to the head page. To that
end switch to for_each_compound_head() does most of the work.

set_page_dirty() needs no adjustment as it's a nop for
non-dirty head pages and it doesn't operate on tail pages.

This considerably improves unpinning of pages with THP and
hugetlbfs:

- THP
gup_test -t -m 16384 -r 10 [-L|-a] -S -n 512 -w
PIN_LONGTERM_BENCHMARK (put values): ~87.6k us -> ~23.2k us

- 16G with 1G huge page size
gup_test -f /mnt/huge/file -m 16384 -r 10 [-L|-a] -S -n 512 -w
PIN_LONGTERM_BENCHMARK: (put values): ~87.6k us -> ~27.5k us

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
---
mm/gup.c | 29 +++++++++++------------------
1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index d1549c61c2f6..5a3dd235017a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -270,20 +270,15 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
bool make_dirty)
{
unsigned long index;
-
- /*
- * TODO: this can be optimized for huge pages: if a series of pages is
- * physically contiguous and part of the same compound page, then a
- * single operation to the head page should suffice.
- */
+ struct page *head;
+ unsigned int ntails;

if (!make_dirty) {
unpin_user_pages(pages, npages);
return;
}

- for (index = 0; index < npages; index++) {
- struct page *page = compound_head(pages[index]);
+ for_each_compound_head(index, pages, npages, head, ntails) {
/*
* Checking PageDirty at this point may race with
* clear_page_dirty_for_io(), but that's OK. Two key
@@ -304,9 +299,9 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
* written back, so it gets written back again in the
* next writeback cycle. This is harmless.
*/
- if (!PageDirty(page))
- set_page_dirty_lock(page);
- unpin_user_page(page);
+ if (!PageDirty(head))
+ set_page_dirty_lock(head);
+ put_compound_head(head, ntails, FOLL_PIN);
}
}
EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
@@ -323,6 +318,8 @@ EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
void unpin_user_pages(struct page **pages, unsigned long npages)
{
unsigned long index;
+ struct page *head;
+ unsigned int ntails;

/*
* If this WARN_ON() fires, then the system *might* be leaking pages (by
@@ -331,13 +328,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
*/
if (WARN_ON(IS_ERR_VALUE(npages)))
return;
- /*
- * TODO: this can be optimized for huge pages: if a series of pages is
- * physically contiguous and part of the same compound page, then a
- * single operation to the head page should suffice.
- */
- for (index = 0; index < npages; index++)
- unpin_user_page(pages[index]);
+
+ for_each_compound_head(index, pages, npages, head, ntails)
+ put_compound_head(head, ntails, FOLL_PIN);
}
EXPORT_SYMBOL(unpin_user_pages);

--
2.17.1
\
 
 \ /
  Last update: 2021-02-04 21:30    [W:0.168 / U:1.872 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site