From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 9F31A6B02B4 for ; Fri, 21 Jul 2017 19:01:07 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id 65so6584515wmf.2 for ; Fri, 21 Jul 2017 16:01:07 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id w2si4856247wra.504.2017.07.21.16.01.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Jul 2017 16:01:06 -0700 (PDT) Date: Fri, 21 Jul 2017 16:01:04 -0700 From: Andrew Morton Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever Message-Id: <20170721160104.9f6101b9e8de53638b3b853a@linux-foundation.org> In-Reply-To: <20170720065625.GB9058@dhcp22.suse.cz> References: <20170710074842.23175-1-mhocko@kernel.org> <20170719152014.53a861c57bcb636d6cd9d002@linux-foundation.org> <20170720065625.GB9058@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Mel Gorman , Tetsuo Handa , Rik van Riel , Johannes Weiner , Vlastimil Babka , linux-mm@kvack.org, LKML On Thu, 20 Jul 2017 08:56:26 +0200 Michal Hocko wrote: > > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -1713,9 +1713,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, > > > int file = is_file_lru(lru); > > > struct pglist_data *pgdat = lruvec_pgdat(lruvec); > > > struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; > > > + bool stalled = false; > > > > > > while (unlikely(too_many_isolated(pgdat, file, sc))) { > > > - congestion_wait(BLK_RW_ASYNC, HZ/10); > > > + if (stalled) > > > + return 0; > > > + > > > + /* wait a bit for the reclaimer. */ > > > + schedule_timeout_interruptible(HZ/10); > > > > a) if this task has signal_pending(), this falls straight through > > and I suspect the code breaks? > > It will not break. It will return to the allocation path more quickly > but no over-reclaim will happen and it will/should get throttled there. > So nothing critical. > > > b) replacing congestion_wait() with schedule_timeout_interruptible() > > means this task no longer contributes to load average here and it's > > a (slightly) user-visible change. > > you are right. I am not sure it matters but it might be visible. > > > c) msleep_interruptible() is nicer > > > > d) IOW, methinks we should be using msleep() here? > > OK, I do not have objections. Are you going to squash this in or want a > separate patch explaining all the above? I'd prefer to have a comment explaining why interruptible sleep is being used, because that "what if signal_pending()" case is rather a red flag. Is it the case that fall-through-if-signal_pending() is the *preferred* behaviour? If so, the comment should explain this. If it isn't the preferred behaviour then using uninterruptible sleep sounds better to me, if only because it saves us from having to test a rather tricky and rare case. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org