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mm, thp: avoid unlikely branches for split_huge_pmd

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While doing MADV_DONTNEED on a large area of thp memory, I noticed we
encountered many unlikely() branches in profiles for each backing
hugepage.  This is because zap_pmd_range() would call split_huge_pmd(),
which rechecked the conditions that were already validated, but as part
of an unlikely() branch.

Avoid the unlikely() branch when in a context where pmd is known to be
good for __split_huge_pmd() directly.

Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1610181600300.84525@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Rientjes 2016-12-12 16:42:20 -08:00 • committed by Linus Torvalds
parent 3f5000693f
commit fd60775aea
4 changed files with 6 additions and 4 deletions
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2
mm/mempolicy.c
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@ -496,7 +496,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
page = pmd_page(*pmd);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
split_huge_pmd(vma, pmd, addr);
__split_huge_pmd(vma, pmd, addr, false, NULL);
} else {
get_page(page);
spin_unlock(ptl);