From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD475C6778C for ; Tue, 3 Jul 2018 17:00:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 956DA21386 for ; Tue, 3 Jul 2018 17:00:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="W2+dCzDy" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 956DA21386 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934020AbeGCRAr (ORCPT ); Tue, 3 Jul 2018 13:00:47 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:40707 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932440AbeGCRAp (ORCPT ); Tue, 3 Jul 2018 13:00:45 -0400 Received: by mail-wm0-f66.google.com with SMTP id z13-v6so3046011wma.5 for ; Tue, 03 Jul 2018 10:00:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=6ZXhjE6V9pncHIVkrKXyhz5H/SV6HatopHW3Gb7tPUk=; b=W2+dCzDyaToehKv+5SqvA71dFVMTQwCZNNOIOM87BrlIzdiXSUQI1CMLxW8jT0zwTP rTl6Ki4MUY99fMKOPYH9tzklzICFh6tbemYyA8gghv21C3lX2bpcN9Xv7hM56M0EVvTY xOu4ITKum6EsfJbLOYgdlenNvQJd5Ql4+lN6rJpgXCNBGKNm8xf+P/8EBpNZDuhNBNPx gZDlATl2zUYgs2BXKi3tBRV/RjGsFA0UW3ktdDs7/3/H7i48vZSc1sC5mc0NCiU/JB/+ nNwnlx/RqJnLkZFz/0f8G0PkviX2mzpRsLnR6EWkphnfT9ze06cvEZGCZEHDWbI9o4mk aNnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6ZXhjE6V9pncHIVkrKXyhz5H/SV6HatopHW3Gb7tPUk=; b=FSwRPS89W/88/KiWekZhurvkT89p//t442eBkTpOJdH0jU9ue5VFyYUEnme4Lv0nFK Qs3plPwCStQuhc6qh7Nthb8Gqvs079fs1OOn1vGdWPmZkijywgicFwobV1nzrLxhySdD jVlQ51qzahldN7GsJwEC6IjLaxrj3F6zwlh3PWgqgx3eCDlBMw6SikDLUbKrd8dOH83B KItzimiDQJZWH6cUdxJCBGqpVLEc4neKtUm+Yu9ZfNuMNQE7YJsIHhoUsVf+jPOiyD8V maGh8xBZF7ermE/Wp5/jUCAhb8o4YMjBZyu9bJzREj03H4AZyMeKc/PHs8t7+d3lpBJ1 XksQ== X-Gm-Message-State: APt69E1OcRY+a4uncrJwc9k7nKFHmOSjxVkTqbudlhOdYtj8y6VwktWg jCgLQT3dyBmnFRWccMj8gftkeTsO+FD/TQSTxGMBWA== X-Google-Smtp-Source: AAOMgpcYT2PTTP6Nc6t2fK3UeOlIA7g1tdGlsRmG2lgabrQAqi9S8PR35hQe6OgqVZ5ZhTlgqnt/QvtyNCbmiScrwps= X-Received: by 2002:a1c:c501:: with SMTP id v1-v6mr12180964wmf.112.1530637244031; Tue, 03 Jul 2018 10:00:44 -0700 (PDT) MIME-Version: 1.0 References: <153063036670.1818.16010062622751502.stgit@localhost.localdomain> <153063054586.1818.6041047871606697364.stgit@localhost.localdomain> <20180703152723.GB21590@bombadil.infradead.org> In-Reply-To: From: Shakeel Butt Date: Tue, 3 Jul 2018 10:00:32 -0700 Message-ID: Subject: Re: [PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker To: Kirill Tkhai Cc: Matthew Wilcox , Vladimir Davydov , Alexander Viro , Johannes Weiner , Michal Hocko , Thomas Gleixner , Philippe Ombredanne , stummala@codeaurora.org, gregkh@linuxfoundation.org, Stephen Rothwell , Roman Gushchin , mka@chromium.org, Tetsuo Handa , Chris Wilson , longman@redhat.com, Minchan Kim , Huang Ying , Mel Gorman , jbacik@fb.com, Guenter Roeck , LKML , Linux MM , lirongqing@baidu.com, Andrey Ryabinin , Andrew Morton , Paul McKenney Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 3, 2018 at 9:17 AM Kirill Tkhai wrote: > > Hi, Shakeel, > > On 03.07.2018 18:46, Shakeel Butt wrote: > > On Tue, Jul 3, 2018 at 8:27 AM Matthew Wilcox wrote: > >> > >> On Tue, Jul 03, 2018 at 06:09:05PM +0300, Kirill Tkhai wrote: > >>> +++ b/mm/vmscan.c > >>> @@ -169,6 +169,49 @@ unsigned long vm_total_pages; > >>> static LIST_HEAD(shrinker_list); > >>> static DECLARE_RWSEM(shrinker_rwsem); > >>> > >>> +#ifdef CONFIG_MEMCG_KMEM > >>> +static DEFINE_IDR(shrinker_idr); > >>> +static int shrinker_nr_max; > >> > >> So ... we've now got a list_head (shrinker_list) which contains all of > >> the shrinkers, plus a shrinker_idr which contains the memcg-aware shrinkers? > >> > >> Why not replace the shrinker_list with the shrinker_idr? It's only used > >> twice in vmscan.c: > >> > >> void register_shrinker_prepared(struct shrinker *shrinker) > >> { > >> down_write(&shrinker_rwsem); > >> list_add_tail(&shrinker->list, &shrinker_list); > >> up_write(&shrinker_rwsem); > >> } > >> > >> list_for_each_entry(shrinker, &shrinker_list, list) { > >> ... > >> > >> The first is simply idr_alloc() and the second is > >> > >> idr_for_each_entry(&shrinker_idr, shrinker, id) { > >> > >> I understand there's a difference between allocating the shrinker's ID and > >> adding it to the list. You can do this by calling idr_alloc with NULL > >> as the pointer, and then using idr_replace() when you want to add the > >> shrinker to the list. idr_for_each_entry() skips over NULL entries. > >> > >> This will actually reduce the size of each shrinker and be more > >> cache-efficient when calling the shrinkers. I think we can also get > >> rid of the shrinker_rwsem eventually, but let's leave it for now. > > > > Can you explain how you envision shrinker_rwsem can be removed? I am > > very much interested in doing that. > > Have you tried to do some games with SRCU? It looks like we just need to > teach count_objects() and scan_objects() to work with semi-destructed > shrinkers. Though, this looks this will make impossible to introduce > shrinkers, which do synchronize_srcu() in scan_objects() for example. > Not sure, someone will actually use this, and this is possible to consider > as limitation. > Hi Kirill, I tried SRCU and the discussion is at https://lore.kernel.org/lkml/20171117173521.GA21692@infradead.org/T/#u Paul E. McKenney suggested to enable SRCU unconditionally. So, to use SRCU for shrinkers, we first have to push unconditional SRCU. Tetsuo had another lockless solution which was a bit involved but does not depend on SRCU. thanks, Shakeel