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pagewalk: only split huge pages when necessary

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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.

[[email protected]: coding-style fixes]
Signed-off-by: Dave Hansen <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: David Rientjes <[email protected]>
Reviewed-by: Eric B Munson <[email protected]>
Tested-by: Eric B Munson <[email protected]>
Cc: Michael J Wolf <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Matt Mackall <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Dave Hansen 2011-03-22 16:32:56 -07:00 • committed by Linus Torvalds
commit 033193275b
4 changed files with 32 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

24
mm/pagewalk.c
View file

@ -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);