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Message-Id: <201505232342.GAG17682.QJOFOVLHOtSFFM@I-love.SAKURA.ne.jp> Date: Sat, 23 May 2015 23:42:26 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: mhocko@...e.cz Cc: david@...morbit.com, hannes@...xchg.org, akpm@...ux-foundation.org, aarcange@...hat.com, rientjes@...gle.com, vbabka@...e.cz, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 0/9] mm: improve OOM mechanism v2 Michal Hocko wrote: > On Thu 30-04-15 18:44:25, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > I mean we should eventually fail all the allocation types but GFP_NOFS > > > is coming from _carefully_ handled code paths which is an easier starting > > > point than a random code path in the kernel/drivers. So can we finally > > > move at least in this direction? > > > > I agree that all the allocation types can fail unless GFP_NOFAIL is given. > > But I also expect that all the allocation types should not fail unless > > order > PAGE_ALLOC_COSTLY_ORDER or GFP_NORETRY is given or chosen as an OOM > > victim. > > Yeah, let's keep shooting our feet and then look for workarounds to deal > with it... > > > We already experienced at Linux 3.19 what happens if !__GFP_FS allocations > > fails. out_of_memory() is called by pagefault_out_of_memory() when 0x2015a > > (!__GFP_FS) allocation failed. > > I have posted a patch to deal with this > (http://marc.info/?l=linux-mm&m=142770374521952&w=2). There is no real > reason to do the GFP_NOFS from the page fault context just because the > mapping _always_ insists on it. Page fault simply _has_ to be GFP_FS > safe, we are badly broken otherwise. That patch should go in hand with > GFP_NOFS might fail one. I haven't posted it yet because I was waiting > for the merge window to close. > Converting page fault allocations from GFP_NOFS to GFP_KERNEL is a different problem for me. My concern is that failing/stalling GFP_NOFS/GFP_NOIO allocations are more dangerous than GFP_KERNEL allocations. > > This looks to me that !__GFP_FS allocations > > are effectively OOM killer context. It is not fair to kill the thread which > > triggered a page fault, for that thread may not be using so much memory > > (unfair from memory usage point of view) or that thread may be global init > > (unfair because killing the entire system than survive by killing somebody). > > Why would we kill the faulting process? > We can see that processes are killed by SIGBUS if we allow memory allocations by page faults to fail, can't we? I didn't catch what your question is. > > Also, failing the GFP_NOFS/GFP_NOIO allocations which are not triggered by > > a page fault generally causes more damage (e.g. taking filesystem error > > action) than survive by killing somebody. Therefore, I think we should not > > hesitate invoking the OOM killer for !__GFP_FS allocation. > > No, we should fix those places and use proper gfp flags rather than > pretend that the problem doesn't exist and deal with all the side > effectes. Do you think we can identify and fix such places and _backport_ them before customers bother us with unexplained hang up? As Andrew Morton picked up from 1 to 7 of this series, I reposted timeout based OOM killing patch at http://marc.info/?l=linux-mm&m=143239200805478&w=2 . Please check and point out what I'm misunderstanding. > -- > Michal Hocko > SUSE Labs > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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