From: Michal Hocko <firstname.lastname@example.org> To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Andrew Morton <email@example.com>, Johannes Weiner <firstname.lastname@example.org>, David Rientjes <email@example.com>, firstname.lastname@example.org, Yong-Taek Lee <email@example.com> Subject: Re: [PATCH] mm, oom: Tolerate processes sharing mm with different view of oom_score_adj. Date: Wed, 16 Jan 2019 13:19:15 +0100 [thread overview] Message-ID: <20190116121915.GJ24149@dhcp22.suse.cz> (raw) In-Reply-To: <88e10029-f3d9-5bb5-be46-a3547c54de28@I-love.SAKURA.ne.jp> On Wed 16-01-19 20:30:25, Tetsuo Handa wrote: > On 2019/01/16 20:09, Michal Hocko wrote: > > On Wed 16-01-19 19:55:21, Tetsuo Handa wrote: > >> This patch reverts both commit 44a70adec910d692 ("mm, oom_adj: make sure > >> processes sharing mm have same view of oom_score_adj") and commit > >> 97fd49c2355ffded ("mm, oom: kill all tasks sharing the mm") in order to > >> close a race and reduce the latency at __set_oom_adj(), and reduces the > >> warning at __oom_kill_process() in order to minimize the latency. > >> > >> Commit 36324a990cf578b5 ("oom: clear TIF_MEMDIE after oom_reaper managed > >> to unmap the address space") introduced the worst case mentioned in > >> 44a70adec910d692. But since the OOM killer skips mm with MMF_OOM_SKIP set, > >> only administrators can trigger the worst case. > >> > >> Since 44a70adec910d692 did not take latency into account, we can hold RCU > >> for minutes and trigger RCU stall warnings by calling printk() on many > >> thousands of thread groups. Even without calling printk(), the latency is > >> mentioned by Yong-Taek Lee . And I noticed that 44a70adec910d692 is > >> racy, and trying to fix the race will require a global lock which is too > >> costly for rare events. > >> > >> If the worst case in 44a70adec910d692 happens, it is an administrator's > >> request. Therefore, tolerate the worst case and speed up __set_oom_adj(). > > > > I really do not think we care about latency. I consider the overal API > > sanity much more important. Besides that the original report you are > > referring to was never exaplained/shown to represent real world usecase. > > oom_score_adj is not really a an interface to be tweaked in hot paths. > > I do care about the latency. Holding RCU for more than 2 minutes is insane. Creating 8k threads could be considered insane as well. But more seriously. I absolutely do not insist on holding a single RCU section for the whole operation. But that doesn't really mean that we want to revert these changes. for_each_process is by far not only called from this path. -- Michal Hocko SUSE Labs
next prev parent reply other threads:[~2019-01-16 12:19 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-01-16 10:55 Tetsuo Handa 2019-01-16 11:09 ` Michal Hocko 2019-01-16 11:30 ` Tetsuo Handa 2019-01-16 12:19 ` Michal Hocko [this message] 2019-01-16 13:32 ` Tetsuo Handa 2019-01-16 13:41 ` Michal Hocko 2019-01-17 10:40 ` Tetsuo Handa 2019-01-17 15:51 ` Michal Hocko 2019-01-30 22:49 ` [PATCH v2] " Tetsuo Handa 2019-01-31 7:11 ` Michal Hocko 2019-01-31 20:59 ` Tetsuo Handa 2019-02-01 9:14 ` Michal Hocko 2019-02-02 11:06 ` Tetsuo Handa 2019-02-11 15:07 ` Michal Hocko
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