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Date: Thu, 11 Sep 2014 16:52:50 +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 04:28:22 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? > 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. Rafael -- 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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