From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id AC28D6B025F for ; Thu, 20 Jul 2017 06:44:22 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id j194so1993717oib.15 for ; Thu, 20 Jul 2017 03:44:22 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [2001:e42:101:1:202:181:97:72]) by mx.google.com with ESMTPS id d84si5824654oif.169.2017.07.20.03.44.20 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 20 Jul 2017 03:44:21 -0700 (PDT) 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> Date: Thu, 20 Jul 2017 19:44:11 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: 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 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. -- 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