mm: always inline _compound_head() with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP=y

We already force-inline page_fixed_fake_head(), page_is_fake_head() and
PageTail(), however the compiler might decide that _compound_head() is not
worthy to be inlined, because of page_fixed_fake_head().

The result is that, for example, PageAnonExclusive() now might involve a
function call when checking PageHuge(), which performs a
page_folio()->_compound_head() call.  This can lead to a slight regression
of the stress-ng.clone benchmark.

This is not super-urgent to fix, but always inlining _compound_head()
seems like the obvious thing to do for this primitive, similar to the
other ones.

This change restores the slight regression and a compilation with
CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP=y shows no relevant bloat [2]:

	add/remove: 15/14 grow/shrink: 79/87 up/down: 12836/-13917 (-1081)
	...
	Total: Before=32786363, After=32785282, chg -0.00%

[1] https://lkml.kernel.org/r/[email protected]
[2] https://lore.kernel.org/all/[email protected]/

Link: https://lkml.kernel.org/r/[email protected]
Fixes: c0bff412e67b ("mm: allow anon exclusive check over hugetlb tail pages")
Signed-off-by: David Hildenbrand <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Tested-by: Yin Fengwei <[email protected]>
Cc: Peter Xu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 17175a328e6b..2515ae85f191 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -232,7 +232,7 @@ static __always_inline int page_is_fake_head(const struct page *page)
 	return page_fixed_fake_head(page) != page;
 }
 
-static inline unsigned long _compound_head(const struct page *page)
+static __always_inline unsigned long _compound_head(const struct page *page)
 {
 	unsigned long head = READ_ONCE(page->compound_head);