From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 3 Apr 2018 14:19:50 +0200 From: Michal Hocko To: Matthew Wilcox Cc: Tetsuo Handa , 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. Message-ID: <20180403121950.GW5501@dhcp22.suse.cz> References: <1522322870-4335-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180329143003.c52ada618be599c5358e8ca2@linux-foundation.org> <201803301934.DHF12420.SOFFJQMLVtHOOF@I-love.SAKURA.ne.jp> <20180403121414.GD5832@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180403121414.GD5832@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: 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. -- Michal Hocko SUSE Labs