From 2fd86a07c9ac50dfbc5eef3c69ef6e5d370f3b28 Mon Sep 17 00:00:00 2001 From: Kairui Song Date: Tue, 2 Aug 2022 01:31:55 +0800 Subject: [PATCH] mm/util: reduce stack usage of folio_mapcount folio_test_hugetlb() 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 Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- mm/util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/util.c b/mm/util.c index c9439c66d8cf..f0cf92b8826e 100644 --- a/mm/util.c +++ b/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 */ -- 2.11.0