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authorDave Hansen <dave@linux.vnet.ibm.com>2011-03-22 16:32:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:04 -0700
commit033193275b3ffcfe7f3fde7b569f3d207f6cd6a0 (patch)
treefc65fa02248f855f0f63e087f35a507b6abb5617 /mm/pagewalk.c
parent278df9f451dc71dcd002246be48358a473504ad0 (diff)
downloadlinux-033193275b3ffcfe7f3fde7b569f3d207f6cd6a0.tar.gz
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 <dave@linux.vnet.ibm.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Acked-by: David Rientjes <rientjes@google.com> Reviewed-by: Eric B Munson <emunson@mgebm.net> Tested-by: Eric B Munson <emunson@mgebm.net> Cc: Michael J Wolf <mjwolf@us.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Matt Mackall <mpm@selenic.com> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/pagewalk.c')
-rw-r--r--mm/pagewalk.c24
1 files changed, 20 insertions, 4 deletions
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 7cfa6ae0230..c3450d53361 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);