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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=no 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 1285FC48BCD for ; Wed, 9 Jun 2021 05:34:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBD82610A5 for ; Wed, 9 Jun 2021 05:34:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232308AbhFIFgl (ORCPT ); Wed, 9 Jun 2021 01:36:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:50104 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230222AbhFIFgl (ORCPT ); Wed, 9 Jun 2021 01:36:41 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D36E3610A5; Wed, 9 Jun 2021 05:34:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1623216875; bh=ojxH3o3H0Mqq+n9f5YLeEz8IbAGLfvn8g3b7SARtU/E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=gHu+JJrnCVvAMVDMFa6ztvhdY0H/mRd/fOS7SkAR7PaSe19nmbVVMCI/kVltOA4FI rwZ6ZagtboTpOv9Y5pEdZKnNpYMK3upW276FGhQTfVkZ1u/yYV1dQt0rt1VZ43fpch Rc3s7CYewdGHmDnPWBmRrIEm6BPzZqA3ywhiLNL8= Date: Tue, 8 Jun 2021 22:34:34 -0700 From: Andrew Morton To: Dennis Zhou Cc: Roman Gushchin , Tejun Heo , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Jan Kara , Dave Chinner , cgroups@vger.kernel.org Subject: Re: [PATCH v9 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Message-Id: <20210608223434.25efb827a66f10ad36f7fe0b@linux-foundation.org> In-Reply-To: References: <20210608230225.2078447-1-guro@fb.com> <20210608230225.2078447-9-guro@fb.com> <20210608171237.be2f4223de89458841c10fd4@linux-foundation.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, 9 Jun 2021 00:37:10 +0000 Dennis Zhou wrote: > On Tue, Jun 08, 2021 at 05:23:34PM -0700, Roman Gushchin wrote: > > On Tue, Jun 08, 2021 at 05:12:37PM -0700, Andrew Morton wrote: > > > On Tue, 8 Jun 2021 16:02:25 -0700 Roman Gushchin wrote: > > > > > > > Asynchronously try to release dying cgwbs by switching attached inodes > > > > to the nearest living ancestor wb. It helps to get rid of per-cgroup > > > > writeback structures themselves and of pinned memory and block cgroups, > > > > which are significantly larger structures (mostly due to large per-cpu > > > > statistics data). This prevents memory waste and helps to avoid > > > > different scalability problems caused by large piles of dying cgroups. > > > > > > > > Reuse the existing mechanism of inode switching used for foreign inode > > > > detection. To speed things up batch up to 115 inode switching in a > > > > single operation (the maximum number is selected so that the resulting > > > > struct inode_switch_wbs_context can fit into 1024 bytes). Because > > > > every switching consists of two steps divided by an RCU grace period, > > > > it would be too slow without batching. Please note that the whole > > > > batch counts as a single operation (when increasing/decreasing > > > > isw_nr_in_flight). This allows to keep umounting working (flush the > > > > switching queue), however prevents cleanups from consuming the whole > > > > switching quota and effectively blocking the frn switching. > > > > > > > > A cgwb cleanup operation can fail due to different reasons (e.g. not > > > > enough memory, the cgwb has an in-flight/pending io, an attached inode > > > > in a wrong state, etc). In this case the next scheduled cleanup will > > > > make a new attempt. An attempt is made each time a new cgwb is offlined > > > > (in other words a memcg and/or a blkcg is deleted by a user). In the > > > > future an additional attempt scheduled by a timer can be implemented. > > > > > > > > ... > > > > > > > > +/* > > > > + * Maximum inodes per isw. A specific value has been chosen to make > > > > + * struct inode_switch_wbs_context fit into 1024 bytes kmalloc. > > > > + */ > > > > +#define WB_MAX_INODES_PER_ISW 115 > > > > > > Can't we do 1024/sizeof(struct inode_switch_wbs_context)? > > > > It must be something like > > DIV_ROUND_DOWN_ULL(1024 - sizeof(struct inode_switch_wbs_context), sizeof(struct inode *)) + 1 > > Sorry to keep popping in for 1 offs but maybe this instead? I think the > above would result in > 1024 kzalloc() call. > > DIV_ROUND_DOWN_ULL(max(1024 - sizeof(struct inode_switch_wbs_context), sizeof(struct inode *)), > sizeof(struct inode *)) > > might need max_t not sure. Unclear to me why plain old division won't work, but whatever. Please figure it out? "115" is too sad to live!