From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 5285C6B0038 for ; Thu, 28 Sep 2017 17:02:32 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id j16so6382953pga.6 for ; Thu, 28 Sep 2017 14:02:32 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id z131si2027528pgz.239.2017.09.28.14.02.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Sep 2017 14:02:31 -0700 (PDT) Date: Thu, 28 Sep 2017 14:02:30 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: Make count list_lru_one::nr_items lockless Message-Id: <20170928140230.a9a0cd44a09eae9441a83bdc@linux-foundation.org> In-Reply-To: References: <150583358557.26700.8490036563698102569.stgit@localhost.localdomain> <20170927141530.25286286fb92a2573c4b548f@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai Cc: vdavydov.dev@gmail.com, apolyakov@beget.ru, linux-kernel@vger.kernel.org, linux-mm@kvack.org, aryabinin@virtuozzo.com On Thu, 28 Sep 2017 10:48:55 +0300 Kirill Tkhai wrote: > >> This patch aims to make super_cache_count() (and other functions, > >> which count LRU nr_items) more effective. > >> It allows list_lru_node::memcg_lrus to be RCU-accessed, and makes > >> __list_lru_count_one() count nr_items lockless to minimize > >> overhead introduced by locking operation, and to make parallel > >> reclaims more scalable. > > > > And... what were the effects of the patch? Did you not run the same > > performance tests after applying it? > > I've just detected the such high usage of shrink slab on production node. It's rather > difficult to make it use another kernel, than it uses, only kpatches are possible. > So, I haven't estimated how it acts on node's performance. > On test node I see, that the patch obviously removes raw_spin_lock from perf profile. > So, it's a little bit untested in this way. Well that's a problem. The patch increases list_lru.o text size by a lot (4800->5696) which will have a cost. And we don't have proof that any benefit is worth that cost. It shouldn't be too hard to cook up a synthetic test to trigger memcg slab reclaim and then run a before-n-after benchmark? -- 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