From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org, surenb@google.com
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org,
hillf.zj@alibaba-inc.com, minchan@kernel.org,
mgorman@techsingularity.net, ying.huang@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
timmurray@google.com, tkjos@google.com
Subject: Re: [PATCH v2] mm: terminate shrink_slab loop if signal is pending
Date: Sun, 10 Dec 2017 20:37:59 +0900 [thread overview]
Message-ID: <201712102037.IEB12405.OLFOMtSOQFVHFJ@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20171210101311.GA20234@dhcp22.suse.cz>
Michal Hocko wrote:
> > > I agree that making waits/loops killable is generally good. But be sure to be
> > > prepared for the worst case. For example, start __GFP_KILLABLE from "best effort"
> > > basis (i.e. no guarantee that the allocating thread will leave the page allocator
> > > slowpath immediately) and check for fatal_signal_pending() only if
> > > __GFP_KILLABLE is set. That is,
> > >
> > > + /*
> > > + * We are about to die and free our memory.
> > > + * Stop shrinking which might delay signal handling.
> > > + */
> > > + if (unlikely((gfp_mask & __GFP_KILLABLE) && fatal_signal_pending(current)))
> > > + break;
> > >
> > > at shrink_slab() etc. and
> > >
> > > + if ((gfp_mask & __GFP_KILLABLE) && fatal_signal_pending(current))
> > > + goto nopage;
> > >
> > > at __alloc_pages_slowpath().
> >
> > I was thinking about something similar and will experiment to see if
> > this solves the problem and if it has any side effects. Anyone sees
> > any obvious problems with this approach?
>
> Tetsuo has been proposing this flag in the past and I've had objections
> why this is not a great idea. I do not have any link handy but the core
> objection was that the semantic would be too fuzzy. All the allocations
> in the same context would have to be killable for this flag to have any
> effect. Spreading it all over the kernel is simply not feasible.
>
Refusing __GFP_KILLABLE based on "All the allocations in the same context
would have to be killable" does not make sense. Outside of MM, we update
code to use _killable version step by step based on best effort basis.
People don't call efforts to change like
func1() {
// As of this point it is easy to bail out.
if (mutex_lock_killable(&lock1) == 0) {
func2();
mutex_unlock(&lock1);
}
}
func2() {
mutex_lock(&lock2);
// Do something which is not possible to bail out for now.
mutex_unlock(&lock2);
}
pointless.
If you insist on "All the allocations in the same context would
have to be killable", then we will offload all activities to some
kernel thread.
next prev parent reply other threads:[~2017-12-10 11:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-08 1:23 [PATCH v2] mm: terminate shrink_slab loop if signal is pending Suren Baghdasaryan
2017-12-08 8:22 ` Michal Hocko
2017-12-08 11:36 ` Tetsuo Handa
2017-12-08 11:48 ` Michal Hocko
2017-12-08 14:03 ` Tetsuo Handa
2017-12-08 18:06 ` Suren Baghdasaryan
2017-12-09 8:08 ` Tetsuo Handa
2017-12-10 10:17 ` Michal Hocko
2017-12-11 21:05 ` Suren Baghdasaryan
2017-12-10 10:13 ` Michal Hocko
2017-12-10 11:37 ` Tetsuo Handa [this message]
2017-12-11 21:12 ` Suren Baghdasaryan
2017-12-08 21:02 ` David Rientjes
2017-12-09 3:16 ` Suren Baghdasaryan
2017-12-09 12:44 ` Tetsuo Handa
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