Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965047AbdGTKoP (ORCPT ); Thu, 20 Jul 2017 06:44:15 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:48378 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934402AbdGTKoN (ORCPT ); Thu, 20 Jul 2017 06:44:13 -0400 To: hughd@google.com, mhocko@kernel.org Cc: akpm@linux-foundation.org, mgorman@suse.de, riel@redhat.com, hannes@cmpxchg.org, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mhocko@suse.com Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever From: Tetsuo Handa References: <20170710074842.23175-1-mhocko@kernel.org> In-Reply-To: Message-Id: <201707201944.IJI05796.VLFJFFtSQMOOOH@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Thu, 20 Jul 2017 19:44:11 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1951 Lines: 51 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. Roughly speaking, there is a moment where shrink_inactive_list() acts like below. bool got_mutex = false; if (!current_is_kswapd()) { if (mutex_lock_killable(&pgdat->too_many_isolated)) return SWAP_CLUSTER_MAX; got_mutex = true; } // kswapd is blocked here waiting for !current_is_kswapd(). if (got_mutex) mutex_unlock(&pgdat->too_many_isolated); > > 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 don't know what your actual patch looks like, but the problem is that pgdat->too_many_isolated waits for kswapd while kswapd waits for pgdat->too_many_isolated; nobody can unlock pgdat->too_many_isolated if once we hit it.