Messages in this thread | | | Date | Tue, 09 Dec 2014 10:24:27 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCH 2/3] mm: page_isolation: remove unnecessary freepage_migratetype check for unused page |
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On 12/09/2014 08:51 AM, Weijie Yang wrote: > when we test the pages in a range is free or not, there is a little > chance we encounter some page which is not in buddy but page_count is 0. > That means that page could be in the page-freeing path but not in the > buddy freelist, such as in pcplist
This shouldn't happen anymore IMHO. The pageblock is marked as MIGRATE_ISOLATE and then a lru+pcplist drain is performed. Nothing should be left on pcplist - anything newly freed goes directly to free lists. Hm, maybe it could be on lru cache, but that holds a page reference IIRC, so this test won't pass.
> or wait for the zone->lock which the > tester is holding.
That could maybe happen, but is it worth testing? If yes, please add it in a comment to the code.
> Back to the freepage_migratetype, we use it for a cached value for decide > which free-list the page go when freeing page. If the pageblock is isolated > the page will go to free-list[MIGRATE_ISOLATE] even if the cached type is > not MIGRATE_ISOLATE, the commit ad53f92e(fix incorrect isolation behavior > by rechecking migratetype) patch series have ensure this. > > So the freepage_migratetype check for page_count==0 page in > __test_page_isolated_in_pageblock() is meaningless. > This patch removes the unnecessary freepage_migratetype check. > > Signed-off-by: Weijie Yang <weijie.yang@samsung.com> > --- > mm/page_isolation.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 6e5174d..f7c9183 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -223,8 +223,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, > page = pfn_to_page(pfn); > if (PageBuddy(page)) > pfn += 1 << page_order(page); > - else if (page_count(page) == 0 && > - get_freepage_migratetype(page) == MIGRATE_ISOLATE) > + else if (page_count(page) == 0) > pfn += 1; > else if (skip_hwpoisoned_pages && PageHWPoison(page)) { > /* >
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