This is version 3 patchset which is improved and minimized version of version 1 to fix freepage accounting problem during memory isolation. I tried different approach in version 2, but, it looks really complicated so I change my mind to improve version 1. You can see version 1, 2 in following links [1] [2], respectively. IMO, this v3 is better than v2, because this is simpler than v2 so better for maintainance and this doesn't change pageblock isolation logic so it is much easier to backport. This problems are found by testing my patchset [3]. There are some race conditions on pageblock isolation and these race cause incorrect freepage count. Before describing bugs itself, I first explain definition of freepage. 1. pages on buddy list are counted as freepage. 2. pages on isolate migratetype buddy list are *not* counted as freepage. 3. pages on cma buddy list are counted as CMA freepage, too. Now, I describe problems and related patch. Patch 1: There is race conditions on getting pageblock migratetype that it results in misplacement of freepages on buddy list, incorrect freepage count and un-availability of freepage. Patch 2: Freepages on pcp list could have stale cached information to determine migratetype of buddy list to go. This causes misplacement of freepages on buddy list and incorrect freepage count. Patch 4: Merging between freepages on different migratetype of pageblocks will cause freepages accouting problem. This patch fixes it. Without patchset [3], above problem doesn't happens on my CMA allocation test, because CMA reserved pages aren't used at all. So there is no chance for above race. With patchset [3], I did simple CMA allocation test and get below result. - Virtual machine, 4 cpus, 1024 MB memory, 256 MB CMA reservation - run kernel build (make -j16) on background - 30 times CMA allocation(8MB * 30 = 240MB) attempts in 5 sec interval - Result: more than 5000 freepage count are missed With patchset [3] and this patchset, I found that no freepage count are missed so that I conclude that problems are solved. These problems can be possible on memory hot remove users, although I didn't check it further. This patchset is based on linux-next-20140826. Please see individual patches for more information. Thanks. [1]: https://lkml.org/lkml/2014/7/4/79 [2]: lkml.org/lkml/2014/8/6/52 [3]: Aggressively allocate the pages on cma reserved memory https://lkml.org/lkml/2014/5/30/291 Joonsoo Kim (4): mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype mm/page_alloc: add freepage on isolate pageblock to correct buddy list mm/page_alloc: move migratetype recheck logic to __free_one_page() mm/page_alloc: restrict max order of merging on isolated pageblock include/linux/mmzone.h | 4 ++++ include/linux/page-isolation.h | 8 ++++++++ mm/page_alloc.c | 28 +++++++++++++++++++--------- mm/page_isolation.c | 2 ++ 4 files changed, 33 insertions(+), 9 deletions(-) -- 1.7.9.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>