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Message-ID: <1507312.nQ09A9EeVa@vostro.rjw.lan> Date: Sun, 14 Sep 2014 18:39:54 +0200 From: "Rafael J. Wysocki" <rjw@...ysocki.net> To: Michal Hocko <mhocko@...e.cz> Cc: Tejun Heo <tj@...nel.org>, Cong Wang <xiyou.wangcong@...il.com>, LKML <linux-kernel@...r.kernel.org>, David Rientjes <rientjes@...gle.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [Patch v4 1/2] freezer: check OOM kill while being frozen On Thursday, September 11, 2014 04:45:09 PM Michal Hocko wrote: > On Thu 11-09-14 16:52:50, Rafael J. Wysocki wrote: > > On Thursday, September 11, 2014 04:28:22 PM Michal Hocko wrote: > > > On Thu 11-09-14 16:32:50, Rafael J. Wysocki wrote: > > > > On Thursday, September 11, 2014 04:10:51 PM Michal Hocko wrote: > > > > > On Thu 11-09-14 16:26:56, Rafael J. Wysocki wrote: > > > > > > On Thursday, September 11, 2014 04:04:48 PM Michal Hocko wrote: > > > > > > > On Thu 11-09-14 16:17:56, Rafael J. Wysocki wrote: > > > > > > > [...] > > > > > > > > And I'm still wondering if the OOM killer may be made avoid killing frozen > > > > > > > > tasks. > > > > > > > > > > > > > > This is really tricky. OOM killer aims at the biggest memory hog. We > > > > > > > shouldn't ignore it just because it hides into the fridge... So even > > > > > > > if we "fix" oom killer to ignore frozen tasks (which is inherently > > > > > > > racy btw.) then we have a potential problem of freezer abuse (e.g. in > > > > > > > container environments). So I strongly believe that the OOM killer has > > > > > > > to be able to kill a frozen tasks. > > > > > > > > > > > > OK > > > > > > > > > > > > Is the OOM killer the only place where TIF_MEMDIE is set? > > > > > > > > > > Yes. To be precise, lowmemorykiller (staging android thingy), global OOM > > > > > killer and memcg OOM killer. Any other users would be an abuse. > > > > > > > > OK > > > > > > > > So can we ensure that those things don't trigger during system suspend (or > > > > equivalent) and then simply use the TIF_MEMDIE check in __refrigerator()? > > > > > > That would require that no memory allocation triggers OOM killer during > > > suspend. I don't think this will work out. OOM killer is the last resort > > > action. We cannot simply give access to memory reserves just because the > > > current context is in the middle of suspend. > > > > But we can fail the allocation, can't we? > > We already do that by oom_killer_disable after all tasks are frozen in > freeze_processes. This is before all other device specific things are > done so I guess we cannot start killing after any device is suspended, > right? This should be sufficient. Yes, it should. > > > What is the worst thing that might happen when a task is killed in the > > > middle of suspend? I thought that suspend would fail after several > > > attempts to suspend all existing tasks. > > > > The problem is what to do when we need to kill a frozen task. > > > > In that case we need to thaw it and then it will die eventually. Unfortunately, > > it generally can do something undesirable before dying. That may be accessing > > a suspended device, for example. > > OK, I have misunderstood you obviously. I thought we were discussing OOM > while we are in the middle of freezing tasks. After they are frozen > there is no OOM killer as per above. Right. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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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