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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 9DF25C433E0 for ; Fri, 12 Mar 2021 08:22:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C21064FA0 for ; Fri, 12 Mar 2021 08:22:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232148AbhCLIVt (ORCPT ); Fri, 12 Mar 2021 03:21:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:55102 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232183AbhCLIVn (ORCPT ); Fri, 12 Mar 2021 03:21:43 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1615537302; h=from:from:reply-to: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=6Ux0+Pb2clKATA+9uJvqm/OvOlt7xzKyD+cErR9DPO4=; b=EJBuwLOaxbyFyLgDDgpljk5VUnrmwFhCrDLJcCfUQek16R4gG+FpsNdkrr1cFtBbJyEFKv g85L0NRHUq/BHX/53DyK7Kwh/WHCeh4+sTbQIObFLCjobFjxOCqLkxi/606X2LApInYZro KlOUz7gX7ufgWqvu2bJSyPl5/ABUDCA= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7E12DAF26; Fri, 12 Mar 2021 08:21:42 +0000 (UTC) Date: Fri, 12 Mar 2021 09:21:41 +0100 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , joaodias@google.com, surenb@google.com, cgoldswo@codeaurora.org, willy@infradead.org, david@redhat.com, vbabka@suse.cz, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3 2/3] mm: disable LRU pagevec during the migration temporarily Message-ID: References: <20210310161429.399432-1-minchan@kernel.org> <20210310161429.399432-2-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210310161429.399432-2-minchan@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 10-03-21 08:14:28, 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(it is about a fallback to a > sync migration) with 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. > > The new interface is also useful for memory hotplug which currently > drains lru pcp caches after each migration failure. This is rather > suboptimal as it has to disrupt others running during the operation. > With the new interface the operation happens only once. This is also in > line with pcp allocator cache which are disabled for the offlining as > well. > > Signed-off-by: Minchan Kim Looks goot to me Acked-by: Michal Hocko Thanks -- Michal Hocko SUSE Labs