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From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>,
	Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	linux-api@vger.kernel.org, Suren Baghdasaryan <surenb@google.com>,
	Tim Murray <timmurray@google.com>,
	Daniel Colascione <dancol@google.com>,
	Sandeep Patil <sspatil@google.com>,
	Sonny Rao <sonnyrao@google.com>,
	Brian Geffon <bgeffon@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Shakeel Butt <shakeelb@google.com>,
	John Dias <joaodias@google.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Jann Horn <jannh@google.com>,
	alexander.h.duyck@linux.intel.com, sj38.park@gmail.com,
	SeongJae Park <sjpark@amazon.de>
Subject: Re: [PATCH v7 7/7] mm/madvise: allow KSM hints for remote API
Date: Mon, 9 Mar 2020 17:03:32 +0100	[thread overview]
Message-ID: <20200309160332.GS8447@dhcp22.suse.cz> (raw)
In-Reply-To: <34f812b8-df54-eaad-5cf0-335f07da55c6@suse.cz>

On Mon 09-03-20 16:42:43, Vlastimil Babka wrote:
> On 3/9/20 4:19 PM, Oleksandr Natalenko wrote:
> > On Mon, Mar 09, 2020 at 04:08:15PM +0100, Michal Hocko wrote:
> >> On Mon 09-03-20 14:11:17, Oleksandr Natalenko wrote:
> >> > On Fri, Mar 06, 2020 at 05:08:18PM +0100, Vlastimil Babka wrote:
> >> [...]
> >> > > Dunno, it's nice to react to signals quickly, for any proces that gets them, no?
> >> > 
> >> > So, do you mean something like this?
> >> > 
> >> > ===
> >> > diff --git a/mm/ksm.c b/mm/ksm.c
> >> > index 363ec8189561..b39c237cfcf4 100644
> >> > --- a/mm/ksm.c
> >> > +++ b/mm/ksm.c
> >> > @@ -849,7 +849,8 @@ static int unmerge_ksm_pages(struct vm_area_struct *vma,
> >> >  	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
> >> >  		if (ksm_test_exit(vma->vm_mm))
> >> >  			break;
> >> > -		if (signal_pending(current))
> >> > +		if (signal_pending(current) ||
> >> > +		    signal_pending(rcu_dereference(vma->vm_mm->owner)))
> >> >  			err = -ERESTARTSYS;
> >> >  		else
> >> >  			err = break_ksm(vma, addr);
> >> > ===
> >> 
> >> This is broken because mm might be attached to different tasks.
> >> AFAIU this check is meant to allow quick backoff of the _calling_
> >> process so that it doesn't waste time when the context is killed
> >> already. I do not understand why should we care about any other context
> >> here? What is the actual problem this would solve?
> > 
> > I agree with you, but still trying to understand what does Vlastimil mean
> > :).
> 
> Well you wondered if we should stop caring about current, and I said that
> probably wouldn't be nice.
> As for caring about the other task, patch 3/7 does that for
> (MADV_COLD|MADV_PAGEOUT) so I just pointed out that the KSM case doesn't. AFAIU
> if we don't check the signals, we might be blocking the killed task from exiting?

I would have to double check but I do not think this would be a problem
because the remote task should take mmget to prevent address space to
vanish under its feet. That should also rule out the exclusive mmap_sem
usage from the exit path.
-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2020-03-09 16:03 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-02 19:36 [PATCH v7 0/7] introduce memory hinting API for external process Minchan Kim
2020-03-02 19:36 ` [PATCH v7 1/7] mm: pass task and mm to do_madvise Minchan Kim
2020-03-05 15:48   ` Vlastimil Babka
2020-05-08 18:21     ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 2/7] mm: introduce external memory hinting API Minchan Kim
2020-03-03 10:33   ` kbuild test robot
2020-03-03 14:57     ` Minchan Kim
2020-03-05 18:15   ` Vlastimil Babka
2020-03-10 22:20     ` Minchan Kim
2020-03-11  0:36       ` Minchan Kim
2020-03-12 12:40       ` Vlastimil Babka
2020-03-12 20:23         ` Minchan Kim
2020-05-08 18:33           ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 3/7] mm: check fatal signal pending of target process Minchan Kim
2020-03-06 10:22   ` Vlastimil Babka
2020-03-10 22:24     ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 4/7] pid: move pidfd_get_pid function to pid.c Minchan Kim
2020-03-06 10:57   ` Vlastimil Babka
2020-03-06 11:14   ` Christian Brauner
2020-03-02 19:36 ` [PATCH v7 5/7] mm: support both pid and pidfd for process_madvise Minchan Kim
2020-03-06 11:14   ` Vlastimil Babka
2020-03-11  0:42     ` Minchan Kim
2020-05-08 18:36       ` Minchan Kim
2020-05-08 23:04         ` Andrew Morton
2020-05-09 12:48           ` Christian Brauner
2020-05-09 23:14             ` Minchan Kim
2020-05-12 19:55               ` Suren Baghdasaryan
2020-03-02 19:36 ` [PATCH v7 6/7] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-03-06 12:52   ` Vlastimil Babka
2020-03-06 13:03     ` Oleksandr Natalenko
2020-03-06 16:03       ` Vlastimil Babka
2020-03-09 12:30         ` Oleksandr Natalenko
2020-03-10 22:28           ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 7/7] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-03-06 13:13   ` Vlastimil Babka
2020-03-06 13:41     ` Oleksandr Natalenko
2020-03-06 16:08       ` Vlastimil Babka
2020-03-09 13:11         ` Oleksandr Natalenko
2020-03-09 15:08           ` Michal Hocko
2020-03-09 15:19             ` Oleksandr Natalenko
2020-03-09 15:42               ` Vlastimil Babka
2020-03-09 16:03                 ` Michal Hocko [this message]
2020-06-11  2:21   ` Jann Horn
2020-03-02 21:16 ` [PATCH v7 0/7] introduce memory hinting API for external process Andrew Morton
2020-03-02 21:42   ` Minchan Kim

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