+ mm-util-reduce-stack-usage-of-folio_mapcount.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@tencent.com>
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@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@tencent.com are

mm-util-reduce-stack-usage-of-folio_mapcount.patch