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=-10.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS 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 13B9EC6377B for ; Wed, 21 Jul 2021 20:18:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2B6461244 for ; Wed, 21 Jul 2021 20:18:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233756AbhGUThd (ORCPT ); Wed, 21 Jul 2021 15:37:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:48436 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232808AbhGUThc (ORCPT ); Wed, 21 Jul 2021 15:37:32 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1300A61241; Wed, 21 Jul 2021 20:18:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1626898687; bh=KpKie0V9uJpTeQXpAAJt4nx7YvVtsE+ZBn1/F/fZfXI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VDltrvXEOVg5w7OY09xeW+N4MxtMN9jQ2OrPVJJsPdn+9/rlgOFK7U9uroEpYTkLd VdQOjrNeJxGGOuAUQxJDisPxQC1VVaDG26kMCo1YGLLmVJFbZCBaPeaNuEsJRKF9eJ tdU0RQ+uppYkUPsjPoZMkuKRjcahDmf7aFkM40WY= Date: Wed, 21 Jul 2021 13:18:06 -0700 From: Andrew Morton To: Charan Teja Reddy Cc: vbabka@suse.cz, rientjes@google.com, nigupta@nvidia.com, khalid.aziz@oracle.com, vinmenon@codeaurora.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH resend] mm: compaction: optimize proactive compaction deferrals Message-Id: <20210721131806.5898dab3e329940fd8bd2db6@linux-foundation.org> In-Reply-To: <1626869599-25412-1-git-send-email-charante@codeaurora.org> References: <1626869599-25412-1-git-send-email-charante@codeaurora.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; 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-kernel@vger.kernel.org On Wed, 21 Jul 2021 17:43:19 +0530 Charan Teja Reddy wrote: > Vlastimil Babka figured out that when fragmentation score didn't go down > across the proactive compaction i.e. when no progress is made, next wake > up for proactive compaction is deferred for 1 << > COMPACT_MAX_DEFER_SHIFT, i.e. 64 times, with each wakeup interval of > HPAGE_FRAG_CHECK_INTERVAL_MSEC(=500). In each of this wakeup, it just > decrement 'proactive_defer' counter and goes sleep i.e. it is getting > woken to just decrement a counter. The same deferral time can also > achieved by simply doing the HPAGE_FRAG_CHECK_INTERVAL_MSEC << > COMPACT_MAX_DEFER_SHIFT thus unnecessary wakeup of kcompact thread is > avoided thus also removes the need of 'proactive_defer' thread counter. > > @@ -2902,23 +2903,30 @@ static int kcompactd(void *p) > > trace_mm_compaction_kcompactd_sleep(pgdat->node_id); > if (wait_event_freezable_timeout(pgdat->kcompactd_wait, > - kcompactd_work_requested(pgdat), > - msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) { > + kcompactd_work_requested(pgdat), timeout)) { > > psi_memstall_enter(&pflags); > kcompactd_do_work(pgdat); > psi_memstall_leave(&pflags); > + /* > + * Reset the timeout value. The defer timeout by > + * proactive compaction can effectively lost > + * here but that is fine as the condition of the > + * zone changed substantionally and carrying on > + * with the previous defer is not useful. > + */ > + timeout = default_timeout; > continue; I find this comment hard to follow. Is this better? --- a/mm/compaction.c~mm-compaction-optimize-proactive-compaction-deferrals-fix +++ a/mm/compaction.c @@ -2909,11 +2909,11 @@ static int kcompactd(void *p) kcompactd_do_work(pgdat); psi_memstall_leave(&pflags); /* - * Reset the timeout value. The defer timeout by - * proactive compaction can effectively lost - * here but that is fine as the condition of the - * zone changed substantionally and carrying on - * with the previous defer is not useful. + * Reset the timeout value. The defer timeout from + * proactive compaction is lost here but that is fine + * as the condition of the zone changing substantionally + * then carrying on with the previous defer interval is + * not useful. */ timeout = default_timeout; continue; _