Subject: + fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem.patch added to -mm tree To: ebiederm@xxxxxxxxxxxx,cwang@xxxxxxxxxxxxxxxx,eric.dumazet@xxxxxxxxx,rientjes@xxxxxxxxxx,stable@xxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Tue, 04 Feb 2014 15:48:38 -0800 The patch titled Subject: fs/file.c:fdtable: avoid triggering OOMs from alloc_fdmem has been added to the -mm tree. Its filename is fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: ebiederm@xxxxxxxxxxxx (Eric W. Biederman) Subject: fs/file.c:fdtable: avoid triggering OOMs from alloc_fdmem Recently due to a spike in connections per second memcached on 3 separate boxes triggered the OOM killer from accept. At the time the OOM killer was triggered there was 4GB out of 36GB free in zone 1. The problem was that alloc_fdtable was allocating an order 3 page (32KiB) to hold a bitmap, and there was sufficient fragmentation that the largest page available was 8KiB. I find the logic that PAGE_ALLOC_COSTLY_ORDER can't fail pretty dubious but I do agree that order 3 allocations are very likely to succeed. There are always pathologies where order > 0 allocations can fail when there are copious amounts of free memory available. Using the pigeon hole principle it is easy to show that it requires 1 page more than 50% of the pages being free to guarantee an order 1 (8KiB) allocation will succeed, 1 page more than 75% of the pages being free to guarantee an order 2 (16KiB) allocation will succeed and 1 page more than 87.5% of the pages being free to guarantee an order 3 allocate will succeed. A server churning memory with a lot of small requests and replies like memcached is a common case that if anything can will skew the odds against large pages being available. Therefore let's not give external applications a practical way to kill linux server applications, and specify __GFP_NORETRY to the kmalloc in alloc_fdmem. Unless I am misreading the code and by the time the code reaches should_alloc_retry in __alloc_pages_slowpath (where __GFP_NORETRY becomes signification). We have already tried everything reasonable to allocate a page and the only thing left to do is wait. So not waiting and falling back to vmalloc immediately seems like the reasonable thing to do even if there wasn't a chance of triggering the OOM killer. Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Cc: Cong Wang <cwang@xxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN fs/file.c~fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem fs/file.c --- a/fs/file.c~fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem +++ a/fs/file.c @@ -34,7 +34,7 @@ static void *alloc_fdmem(size_t size) * vmalloc() if the allocation size will be considered "large" by the VM. */ if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) { - void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN); + void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY); if (data != NULL) return data; } _ Patches currently in -mm which might be from ebiederm@xxxxxxxxxxxx are vmcore-prevent-pt_note-p_memsz-overflow-during-header-update.patch vmcore-prevent-pt_note-p_memsz-overflow-during-header-update-v2.patch fs-filec-fdtable-avoid-triggering-ooms-from-alloc_fdmem.patch kernel-audit-fix-non-modular-users-of-module_init-in-core-code.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html