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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 AB363C433DB for ; Thu, 4 Mar 2021 08:10:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 750B564EFC for ; Thu, 4 Mar 2021 08:10:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236266AbhCDIJd (ORCPT ); Thu, 4 Mar 2021 03:09:33 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:44343 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236161AbhCDIJD (ORCPT ); Thu, 4 Mar 2021 03:09:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614845257; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2c1ILN3q9sGba/2LIo3VeOZCilzIXtGwhnmwt+QTvoc=; b=AGAi4PFqOGoTidLUY9cMvLYttypiqzMepODR/jiEcqfHmStwgAreRXyFg8Ml+gQSFaefJP rbbTIfAud2a0gpdv+/+h+w4GJ1T5kU32vG9Svf/JG2u/cs4ipowMq6oDL2aRqZUN++P8NG X7IqZhPFgvGUZrosm/mzR8AsduYBUE4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-537-Zojm_bYOPQif52QJBmbxEQ-1; Thu, 04 Mar 2021 03:07:34 -0500 X-MC-Unique: Zojm_bYOPQif52QJBmbxEQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4E9AA804023; Thu, 4 Mar 2021 08:07:32 +0000 (UTC) Received: from [10.36.113.171] (ovpn-113-171.ams2.redhat.com [10.36.113.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 99EDA614ED; Thu, 4 Mar 2021 08:07:29 +0000 (UTC) Subject: Re: [PATCH 1/2] mm: disable LRU pagevec during the migration temporarily To: Minchan Kim , Michal Hocko Cc: Andrew Morton , linux-mm , LKML , joaodias@google.com, surenb@google.com, cgoldswo@codeaurora.org, willy@infradead.org, vbabka@suse.cz, linux-fsdevel@vger.kernel.org References: <20210302210949.2440120-1-minchan@kernel.org> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Thu, 4 Mar 2021 09:07:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 03.03.21 21:23, Minchan Kim wrote: > On Wed, Mar 03, 2021 at 01:49:36PM +0100, Michal Hocko wrote: >> On Tue 02-03-21 13:09:48, Minchan Kim wrote: >>> LRU pagevec holds refcount of pages until the pagevec are drained. >>> It could prevent migration since the refcount of the page is greater >>> than the expection in migration logic. To mitigate the issue, >>> callers of migrate_pages drains LRU pagevec via migrate_prep or >>> lru_add_drain_all before migrate_pages call. >>> >>> However, it's not enough because pages coming into pagevec after the >>> draining call still could stay at the pagevec so it could keep >>> preventing page migration. Since some callers of migrate_pages have >>> retrial logic with LRU draining, the page would migrate at next trail >>> but it is still fragile in that it doesn't close the fundamental race >>> between upcoming LRU pages into pagvec and migration so the migration >>> failure could cause contiguous memory allocation failure in the end. >>> >>> To close the race, this patch disables lru caches(i.e, pagevec) >>> during ongoing migration until migrate is done. >>> >>> Since it's really hard to reproduce, I measured how many times >>> migrate_pages retried with force mode below debug code. >>> >>> int migrate_pages(struct list_head *from, new_page_t get_new_page, >>> .. >>> .. >>> >>> if (rc && reason == MR_CONTIG_RANGE && pass > 2) { >>> printk(KERN_ERR, "pfn 0x%lx reason %d\n", page_to_pfn(page), rc); >>> dump_page(page, "fail to migrate"); >>> } >>> >>> The test was repeating android apps launching with cma allocation >>> in background every five seconds. Total cma allocation count was >>> about 500 during the testing. With this patch, the dump_page count >>> was reduced from 400 to 30. >> >> Have you seen any improvement on the CMA allocation success rate? > > Unfortunately, the cma alloc failure rate with reasonable margin > of error is really hard to reproduce under real workload. > That's why I measured the soft metric instead of direct cma fail > under real workload(I don't want to make some adhoc artificial > benchmark and keep tunes system knobs until it could show > extremly exaggerated result to convice patch effect). > > Please say if you belive this work is pointless unless there is > stable data under reproducible scenario. I am happy to drop it. Do you have *some* application that triggers such a high retry count? I'd love to run it along with virtio-mem and report the actual allocation success rate / necessary retries. That could give an indication of how helpful your work would be. Anything that improves the reliability of alloc_contig_range() is of high interest to me. If it doesn't increase the reliability but merely does some internal improvements (less retries), it might still be valuable, but not that important. -- Thanks, David / dhildenb