From: Matthew Wilcox <willy@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
kirill.shutemov@linux.intel.com, riel@redhat.com
Subject: Re: [PATCH] mm: Check for SIGKILL inside dup_mmap() loop.
Date: Tue, 3 Apr 2018 05:25:35 -0700 [thread overview]
Message-ID: <20180403122535.GE5832@bombadil.infradead.org> (raw)
In-Reply-To: <20180403121950.GW5501@dhcp22.suse.cz>
On Tue, Apr 03, 2018 at 02:19:50PM +0200, Michal Hocko wrote:
> On Tue 03-04-18 05:14:14, Matthew Wilcox wrote:
> > On Fri, Mar 30, 2018 at 07:34:59PM +0900, Tetsuo Handa wrote:
> > > Maybe we can make "give up by default upon SIGKILL" and let callers
> > > explicitly say "do not give up upon SIGKILL".
> >
> > I really strongly disapprove of this patch. This GFP flag will be abused
> > like every other GFP flag.
> >
> > > +++ b/mm/page_alloc.c
> > > @@ -4183,6 +4183,13 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
> > > if (current->flags & PF_MEMALLOC)
> > > goto nopage;
> > >
> > > + /* Can give up if caller is willing to give up upon fatal signals */
> > > + if (fatal_signal_pending(current) &&
> > > + !(gfp_mask & (__GFP_UNKILLABLE | __GFP_NOFAIL))) {
> > > + gfp_mask |= __GFP_NOWARN;
> > > + goto nopage;
> > > + }
> > > +
> > > /* Try direct reclaim and then allocating */
> >
> > This part is superficially tempting, although without the UNKILLABLE. ie:
> >
> > + if (fatal_signal_pending(current) && !(gfp_mask & __GFP_NOFAIL)) {
> > + gfp_mask |= __GFP_NOWARN;
> > + goto nopage;
> > + }
> >
> > It makes some sense to me to prevent tasks with a fatal signal pending
> > from being able to trigger reclaim. But I'm worried about what memory
> > allocation failures it might trigger on paths that aren't accustomed to
> > seeing failures.
>
> Please be aware that we _do_ allocate in the exit path. I have a strong
> suspicion that even while fatal signal is pending. Do we really want
> fail those really easily.
I agree. The allocations I'm thinking about are NFS wanting to send
I/Os in order to fsync each file that gets closed. We probably don't
want those to fail. And we definitely don't want to chase around the
kernel adding __GFP_KILLABLE to each place that we discover needs to
allocate on the exit path.
next prev parent reply other threads:[~2018-04-03 12:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-29 11:27 [PATCH] mm: Check for SIGKILL inside dup_mmap() loop Tetsuo Handa
2018-03-29 21:30 ` Andrew Morton
2018-03-30 10:34 ` Tetsuo Handa
2018-04-03 12:14 ` Matthew Wilcox
2018-04-03 12:19 ` Michal Hocko
2018-04-03 12:25 ` Matthew Wilcox [this message]
2018-04-03 14:54 ` Tetsuo Handa
2018-04-03 12:29 ` Tetsuo Handa
2018-04-03 13:06 ` Michal Hocko
2018-04-03 11:16 ` Michal Hocko
2018-04-03 11:32 ` Tetsuo Handa
2018-04-03 11:38 ` Michal Hocko
2018-04-03 11:58 ` Matthew Wilcox
2018-04-03 12:08 ` Michal Hocko
2018-04-07 10:38 ` Tetsuo Handa
2018-04-18 21:44 ` Andrew Morton
2018-04-19 1:54 ` Tetsuo Handa
2018-04-19 2:32 ` Andrew Morton
2018-06-07 22:05 ` Andrew Morton
2018-06-08 17:05 ` Matthew Wilcox
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