From 033193275b3ffcfe7f3fde7b569f3d207f6cd6a0 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Tue, 22 Mar 2011 16:32:56 -0700 Subject: pagewalk: only split huge pages when necessary Right now, if a mm_walk has either ->pte_entry or ->pmd_entry set, it will unconditionally split any transparent huge pages it runs in to. In practice, that means that anyone doing a cat /proc/$pid/smaps will unconditionally break down every huge page in the process and depend on khugepaged to re-collapse it later. This is fairly suboptimal. This patch changes that behavior. It teaches each ->pmd_entry handler (there are five) that they must break down the THPs themselves. Also, the _generic_ code will never break down a THP unless a ->pte_entry handler is actually set. This means that the ->pmd_entry handlers can now choose to deal with THPs without breaking them down. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Dave Hansen Acked-by: Mel Gorman Acked-by: David Rientjes Reviewed-by: Eric B Munson Tested-by: Eric B Munson Cc: Michael J Wolf Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Matt Mackall Cc: Jeremy Fitzhardinge Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/pagewalk.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) (limited to 'mm/pagewalk.c') diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 7cfa6ae..c3450d5 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -33,19 +33,35 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, pmd = pmd_offset(pud, addr); do { +again: next = pmd_addr_end(addr, end); - split_huge_page_pmd(walk->mm, pmd); - if (pmd_none_or_clear_bad(pmd)) { + if (pmd_none(*pmd)) { if (walk->pte_hole) err = walk->pte_hole(addr, next, walk); if (err) break; continue; } + /* + * This implies that each ->pmd_entry() handler + * needs to know about pmd_trans_huge() pmds + */ if (walk->pmd_entry) err = walk->pmd_entry(pmd, addr, next, walk); - if (!err && walk->pte_entry) - err = walk_pte_range(pmd, addr, next, walk); + if (err) + break; + + /* + * Check this here so we only break down trans_huge + * pages when we _need_ to + */ + if (!walk->pte_entry) + continue; + + split_huge_page_pmd(walk->mm, pmd); + if (pmd_none_or_clear_bad(pmd)) + goto again; + err = walk_pte_range(pmd, addr, next, walk); if (err) break; } while (pmd++, addr = next, addr != end); -- cgit v1.1