mm, memory_hotplug: check zone_movable in has_unmovable_pages
Page state checks are racy. Under a heavy memory workload (e.g. stress -m 200 -t 2h) it is quite easy to hit a race window when the page is allocated but its state is not fully populated yet. A debugging patch to dump the struct page state shows has_unmovable_pages: pfn:0x10dfec00, found:0x1, count:0x0 page:ffffea0437fb0000 count:1 mapcount:1 mapping:ffff880e05239841 index:0x7f26e5000 compound_mapcount: 1 flags: 0x5fffffc0090034(uptodate|lru|active|head|swapbacked) Note that the state has been checked for both PageLRU and PageSwapBacked already. Closing this race completely would require some sort of retry logic. This can be tricky and error prone (think of potential endless or long taking loops). Workaround this problem for movable zones at least. Such a zone should only contain movable pages. Commit15c30bc090
("mm, memory_hotplug: make has_unmovable_pages more robust") has told us that this is not strictly true though. Bootmem pages should be marked reserved though so we can move the original check after the PageReserved check. Pages from other zones are still prone to races but we even do not pretend that memory hotremove works for those so pre-mature failure doesn't hurt that much. Link: http://lkml.kernel.org/r/20181106095524.14629-1-mhocko@kernel.org Fixes:15c30bc090
("mm, memory_hotplug: make has_unmovable_pages more robust") Signed-off-by: Michal Hocko <mhocko@suse.com> Reported-by: Baoquan He <bhe@redhat.com> Tested-by: Baoquan He <bhe@redhat.com> Acked-by: Baoquan He <bhe@redhat.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Acked-by: Balbir Singh <bsingharora@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -7788,6 +7788,14 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
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if (PageReserved(page))
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goto unmovable;
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/*
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* If the zone is movable and we have ruled out all reserved
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* pages then it should be reasonably safe to assume the rest
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* is movable.
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*/
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if (zone_idx(zone) == ZONE_MOVABLE)
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continue;
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/*
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* Hugepages are not in LRU lists, but they're movable.
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* We need not scan over tail pages bacause we don't
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