The patch titled
Subject: mm/util: reduce stack usage of folio_mapcount
has been added to the -mm mm-unstable branch. Its filename is
mm-util-reduce-stack-usage-of-folio_mapcount.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-util-reduce-stack-usage-of-folio_mapcount.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: Kairui Song <kasong@xxxxxxxxxxx>
Subject: mm/util: reduce stack usage of folio_mapcount
Date: Tue, 2 Aug 2022 01:31:55 +0800
folio_entire_mapcount() will call PageHeadHuge which is a function call,
and blocks the compiler from recognizing this redundant load.
After rearranging the code, stack usage is dropped from 32 to 24, and
the function size is smaller (tested on GCC 12):
Before:
Stack usage:
mm/util.c:845:5:folio_mapcount 32 static
Size:
0000000000000ea0 00000000000000c7 T folio_mapcount
After:
Stack usage:
mm/util.c:845:5:folio_mapcount 24 static
Size:
0000000000000ea0 00000000000000b0 T folio_mapcount
Link: https://lkml.kernel.org/r/20220801173155.92008-1-ryncsn@xxxxxxxxx
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/util.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/util.c~mm-util-reduce-stack-usage-of-folio_mapcount
+++ a/mm/util.c
@@ -850,10 +850,10 @@ int folio_mapcount(struct folio *folio)
return atomic_read(&folio->_mapcount) + 1;
compound = folio_entire_mapcount(folio);
- nr = folio_nr_pages(folio);
if (folio_test_hugetlb(folio))
return compound;
ret = compound;
+ nr = folio_nr_pages(folio);
for (i = 0; i < nr; i++)
ret += atomic_read(&folio_page(folio, i)->_mapcount) + 1;
/* File pages has compound_mapcount included in _mapcount */
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
mm-util-reduce-stack-usage-of-folio_mapcount.patch
