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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,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 E4A6DC3A59E for ; Mon, 26 Aug 2019 07:43:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B62AB2080C for ; Mon, 26 Aug 2019 07:43:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566805433; bh=M+hTegmHDZh+05dXP2akiotTvv2BNnDxEdumsrM6JZY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=bZ5cxu1nBYYZI/1XavAbCcDqsDZSFsYy816Nqw0OCcSprvetcF97EP2uiXGoSjLxP 8vHgFTA9bPb4H/WFgvuyq+X7IldYSdYkK1hZqlAD3mO+ra2ogJQdYiNNTCzwgaer1x CUumRpB72a574g2oLmKpK4+EyKLrKx+Fmej3eBEE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730204AbfHZHnw (ORCPT ); Mon, 26 Aug 2019 03:43:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:59628 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728198AbfHZHnw (ORCPT ); Mon, 26 Aug 2019 03:43:52 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id ED493AE79; Mon, 26 Aug 2019 07:43:50 +0000 (UTC) Date: Mon, 26 Aug 2019 09:43:50 +0200 From: Michal Hocko To: Yang Shi Cc: kirill.shutemov@linux.intel.com, hannes@cmpxchg.org, vbabka@suse.cz, rientjes@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH -mm] mm: account deferred split THPs into MemAvailable Message-ID: <20190826074350.GE7538@dhcp22.suse.cz> References: <1566410125-66011-1-git-send-email-yang.shi@linux.alibaba.com> <20190822080434.GF12785@dhcp22.suse.cz> <9e4ba38e-0670-7292-ab3a-38af391598ec@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9e4ba38e-0670-7292-ab3a-38af391598ec@linux.alibaba.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 22-08-19 08:33:40, Yang Shi wrote: > > > On 8/22/19 1:04 AM, Michal Hocko wrote: > > On Thu 22-08-19 01:55:25, Yang Shi wrote: [...] > > > And, they seems very common with the common workloads when THP is > > > enabled. A simple run with MariaDB test of mmtest with THP enabled as > > > always shows it could generate over fifteen thousand deferred split THPs > > > (accumulated around 30G in one hour run, 75% of 40G memory for my VM). > > > It looks worth accounting in MemAvailable. > > OK, this makes sense. But your above numbers are really worrying. > > Accumulating such a large amount of pages that are likely not going to > > be used is really bad. They are essentially blocking any higher order > > allocations and also push the system towards more memory pressure. > > That is accumulated number, during the running of the test, some of them > were freed by shrinker already. IOW, it should not reach that much at any > given time. Then the above description is highly misleading. What is the actual number of lingering THPs that wait for the memory pressure in the peak? > > IIUC deferred splitting is mostly a workaround for nasty locking issues > > during splitting, right? This is not really an optimization to cache > > THPs for reuse or something like that. What is the reason this is not > > done from a worker context? At least THPs which would be freed > > completely sound like a good candidate for kworker tear down, no? > > Yes, deferred split THP was introduced to avoid locking issues according to > the document. Memcg awareness would help to trigger the shrinker more often. > > I think it could be done in a worker context, but when to trigger to worker > is a subtle problem. Why? What is the problem to trigger it after unmap of a batch worth of THPs? -- Michal Hocko SUSE Labs