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 57908ECAAD3 for ; Wed, 31 Aug 2022 16:20:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232137AbiHaQUp (ORCPT ); Wed, 31 Aug 2022 12:20:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231828AbiHaQUk (ORCPT ); Wed, 31 Aug 2022 12:20:40 -0400 Received: from out1.migadu.com (out1.migadu.com [91.121.223.63]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA99558DC8; Wed, 31 Aug 2022 09:20:38 -0700 (PDT) Date: Wed, 31 Aug 2022 12:20:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1661962837; 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=iGyIm0136Cqvu8OauWzfpc3vydsg6hlY8VzCbW2wXJg=; b=KVP2c5IAZ3wBXb2/Ad6Xj43ljUfrIdr7gfO4yiBKC2RKOWHohtjtIXVhI3lUJiPDbu8s8A OgKnIfQQ9lSKVfDzWbpXF/ELpw+p0U2uveRKEHmnrSHDmx2oda782PoBDvM4b2hIeOKuns rKESeCwGcppKXEWhmK+nLoA/6gDDxY8= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kent Overstreet To: Mel Gorman Cc: Suren Baghdasaryan , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, ldufour@linux.ibm.com, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, shakeelb@google.com, songmuchun@bytedance.com, arnd@arndb.de, jbaron@akamai.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-mm@kvack.org, iommu@lists.linux.dev, kasan-dev@googlegroups.com, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 03/30] Lazy percpu counters Message-ID: <20220831162030.hzgzhxu3qn6g3k5r@moria.home.lan> References: <20220830214919.53220-1-surenb@google.com> <20220830214919.53220-4-surenb@google.com> <20220831100249.f2o27ri7ho4ma3pe@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220831100249.f2o27ri7ho4ma3pe@suse.de> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Wed, Aug 31, 2022 at 11:02:49AM +0100, Mel Gorman wrote: > On Tue, Aug 30, 2022 at 02:48:52PM -0700, Suren Baghdasaryan wrote: > > From: Kent Overstreet > > > > This patch adds lib/lazy-percpu-counter.c, which implements counters > > that start out as atomics, but lazily switch to percpu mode if the > > update rate crosses some threshold (arbitrarily set at 256 per second). > > > > Signed-off-by: Kent Overstreet > > Why not use percpu_counter? It has a per-cpu counter that is synchronised > when a batch threshold (default 32) is exceeded and can explicitly sync > the counters when required assuming the synchronised count is only needed > when reading debugfs. It doesn't switch from atomic mode to percpu mode when the update rate crosses a threshold like lazy percpu counters does, it allocates all the percpu counters up front - that makes it a non starter here. Also, from my reading of the code... wtf is it even doing, and why would I use it at all? This looks like old grotty code from ext3, it's not even using this_cpu_add() - it does preempt_enable()/disable() just for adding to a local percpu counter! Noooooope.