Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754865AbdGTNW3 (ORCPT ); Thu, 20 Jul 2017 09:22:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:40092 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754726AbdGTNW2 (ORCPT ); Thu, 20 Jul 2017 09:22:28 -0400 Date: Thu, 20 Jul 2017 15:22:25 +0200 From: Michal Hocko To: Hugh Dickins Cc: Andrew Morton , Mel Gorman , Tetsuo Handa , Rik van Riel , Johannes Weiner , Vlastimil Babka , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever Message-ID: <20170720132225.GI9058@dhcp22.suse.cz> References: <20170710074842.23175-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1575 Lines: 37 On Wed 19-07-17 18:54:40, Hugh Dickins wrote: [...] > You probably won't welcome getting into alternatives at this late stage; > but after hacking around it one way or another because of its pointless > lockups, I lost patience with that too_many_isolated() loop a few months > back (on realizing the enormous number of pages that may be isolated via > migrate_pages(2)), and we've been running nicely since with something like: > > bool got_mutex = false; > > if (unlikely(too_many_isolated(pgdat, file, sc))) { > if (mutex_lock_killable(&pgdat->too_many_isolated)) > return SWAP_CLUSTER_MAX; > got_mutex = true; > } > ... > if (got_mutex) > mutex_unlock(&pgdat->too_many_isolated); > > Using a mutex to provide the intended throttling, without an infinite > loop or an arbitrary delay; and without having to worry (as we often did) > about whether those numbers in too_many_isolated() are really appropriate. > No premature OOMs complained of yet. > > But that was on a different kernel, and there I did have to make sure > that PF_MEMALLOC always prevented us from nesting: I'm not certain of > that in the current kernel (but do remember Johannes changing the memcg > end to make it use PF_MEMALLOC too). I offer the preview above, to see > if you're interested in that alternative: if you are, then I'll go ahead > and make it into an actual patch against v4.13-rc. I would rather get rid of any additional locking here and my ultimate goal is to make throttling at the page allocator layer rather than inside the reclaim. -- Michal Hocko SUSE Labs