From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FAC4127B68 for ; Wed, 21 Feb 2024 22:15:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708553706; cv=none; b=S2dogf/ROAwC3hO5ocYOdGlWZmzKPvxoEN2rP807Knp1SBUW/xu4LTo7qNkjmDqPW/x9fS5xx0dQw/HlH/elyggxGYJ4q0nlX1zt3jVRs5sUJ0KROOsYaUx1Di7vJJDrA6a3aUWFWIJEjidL1YwHCjwHHS3vnqbX8f58IIMupek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708553706; c=relaxed/simple; bh=pVsIndEbFUfPsGagLBr+KPbde70KmO6aWFeU/fLbpjI=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=NWJJMWYYd3oCjM/DM0PIO7H0lkapeHc0skSkb/pSjWfYAhOeuG9s3C1W4hTCbR5NhPhUqh1GrPjAQjh/7Abo6VLJyPWHHvHxgfuDbeQWEXohGetDuJrYyYPZC9PIfg/6qyAm0kCfciAP6AaksmOXJRtk9j63KiZ3XFjTVWVKJ/8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=S040VVPj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="S040VVPj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 534B5C433C7; Wed, 21 Feb 2024 22:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1708553705; bh=pVsIndEbFUfPsGagLBr+KPbde70KmO6aWFeU/fLbpjI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=S040VVPjk1Bp+pNjJutpGTQzoGao39dhsaZjMPROjzlanWRpsHOQC+ct+rVacI6Sa p3U5uV3XZfsUIn1nNHhuLbgJV1BIicgGr4lzoIDgjcuItG/aRgh+ItkDr8OvDsARAM L9rx5y1/uww8wzyT8tsYTd1PrybWbYrYlgS3Qikk= Date: Wed, 21 Feb 2024 14:15:04 -0800 From: Andrew Morton To: Baolin Wang Cc: Zi Yan , Vlastimil Babka , mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: compaction: limit the suitable target page order to be less than cc->order Message-Id: <20240221141504.3c3cec674553b4df4bd72ec1@linux-foundation.org> In-Reply-To: <83bc1070-2eb4-4fac-aecf-9cc407003ca2@linux.alibaba.com> References: <20c8fa7c-62ae-4e48-aaec-8b512519cee9@suse.cz> <5277627F-6791-46A1-AFC2-54FBF0DABF1A@nvidia.com> <83bc1070-2eb4-4fac-aecf-9cc407003ca2@linux.alibaba.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 19 Feb 2024 10:55:59 +0800 Baolin Wang wrote: > > > On 2024/2/12 23:00, Zi Yan wrote: > > On 12 Feb 2024, at 4:13, Vlastimil Babka wrote: > > > >> On 1/22/24 14:01, Baolin Wang wrote: > >>> It can not improve the fragmentation if we isolate the target free pages > >>> exceeding cc->order, especially when the cc->order is less than pageblock_order. > >>> For example, suppose the pageblock_order is MAX_ORDER (size is 4M) and cc->order > >>> is 2M THP size, we should not isolate other 2M free pages to be the migration > >>> target, which can not improve the fragmentation. > >>> > >>> Moreover this is also applicable for large folio compaction. > >> > >> So why not Cc: Zi Yan? (done) > >> > > > > Thanks. > > > > Hi Baolin, > > > > How often do you see this happening? > > This is theoretically analyzed from the code inspection. > > >>> Signed-off-by: Baolin Wang > >> > >> I doubt this will make much difference, because if such a larger order free > >> page exists, we shouldn't have a reason to be compacting for a lower order > >> in the first place? > > > > Unless kswapd gets us such a free block in the background right after > > get_page_from_freelist() and before compaction finishes in the allocation > > slow path. > > > > If this happens often and cc->order is not -1, it might be better to stop > > compaction and get_page_from_freelist() to save cycles on unnecessary pfn > > scanning. For completeness, when cc->order == -1, the logic does not change. > > Yes, this is one possible case. There are also some other concurrent > scenarios, such as when compaction is running (after > compaction_suitable()), at the same time, other applications release a > large folio to the free list. In this case, the free large folio > scanning should also be avoided. This went quiet. We have an ack from Mel. Are people OK with sending this change upstream?