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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8916CC433F5 for ; Tue, 19 Apr 2022 17:58:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344216AbiDSSB3 (ORCPT ); Tue, 19 Apr 2022 14:01:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356158AbiDSSBX (ORCPT ); Tue, 19 Apr 2022 14:01:23 -0400 Received: from out1.migadu.com (out1.migadu.com [IPv6:2001:41d0:2:863f::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8610613D61 for ; Tue, 19 Apr 2022 10:58:40 -0700 (PDT) Date: Tue, 19 Apr 2022 10:58:33 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1650391118; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LwMEsoXiVBDMMlTnWr1tF9A5/2DsUEfBfNSdTUYTpLQ=; b=GSeP4KlZhPpf+uMxHvjav5FPXp0dJ579TdtR8KLfaXlePkdpBE1fC+WWHOtb/f2Y2ujT0C wGB6njWc6l5pB8jXYw9Nrrp5C0Rgiq2pRexIanJAIBeZm7haDbH/jW8fuz7j7gtkze/8yP JULqwDoS/c8b/+WlglVpvr6YOWVyYJU= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Mike Rapoport Cc: linux-mm@kvack.org, Andrew Morton , Dave Chinner , linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko , Shakeel Butt , Yang Shi Subject: Re: [PATCH rfc 0/5] mm: introduce shrinker sysfs interface Message-ID: References: <20220416002756.4087977-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 19, 2022 at 09:33:48AM +0300, Mike Rapoport wrote: > On Mon, Apr 18, 2022 at 10:27:34AM -0700, Roman Gushchin wrote: > > On Mon, Apr 18, 2022 at 12:27:36PM +0300, Mike Rapoport wrote: > > > On Fri, Apr 15, 2022 at 05:27:51PM -0700, Roman Gushchin wrote: > > > > There are 50+ different shrinkers in the kernel, many with their own bells and > > > > whistles. Under the memory pressure the kernel applies some pressure on each of > > > > them in the order of which they were created/registered in the system. Some > > > > of them can contain only few objects, some can be quite large. Some can be > > > > effective at reclaiming memory, some not. > > > > > > > > The only existing debugging mechanism is a couple of tracepoints in > > > > do_shrink_slab(): mm_shrink_slab_start and mm_shrink_slab_end. They aren't > > > > covering everything though: shrinkers which report 0 objects will never show up, > > > > there is no support for memcg-aware shrinkers. Shrinkers are identified by their > > > > scan function, which is not always enough (e.g. hard to guess which super > > > > block's shrinker it is having only "super_cache_scan"). They are a passive > > > > mechanism: there is no way to call into counting and scanning of an individual > > > > shrinker and profile it. > > > > > > > > To provide a better visibility and debug options for memory shrinkers > > > > this patchset introduces a /sys/kernel/shrinker interface, to some extent > > > > similar to /sys/kernel/slab. > > > > > > Wouldn't debugfs better fit the purpose of shrinker debugging? > > > > I think sysfs fits better, but not a very strong opinion. > > > > Even though the interface is likely not very useful for the general > > public, big cloud instances might wanna enable it to gather statistics > > (and it's certainly what we gonna do at Facebook) and to provide > > additional data when something is off. They might not have debugfs > > mounted. And it's really similar to /sys/kernel/slab. > > And there is also similar /proc/vmallocinfo so why not /proc/shrinker? ;-) > > I suspect slab ended up in sysfs because nobody suggested to use debugfs > back then. I've been able to track the transition from /proc/slabinfo to > /proc/slubinfo to /sys/kernel/slab, but could not find why Christoph chose > sysfs in the end. > > > Are there any reasons why debugfs is preferable? > > debugfs is more flexible because it's not stable kernel ABI so if there > will be need/desire to change the layout and content of the files with > debugfs it can be done more easily. > > Is this a real problem for Facebook to mount debugfs? ;-) Fair enough, switching to debugfs in the next version. Thanks!