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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 4F766C43441 for ; Thu, 22 Nov 2018 17:05:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1348A20684 for ; Thu, 22 Nov 2018 17:05:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1348A20684 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406143AbeKWDpY (ORCPT ); Thu, 22 Nov 2018 22:45:24 -0500 Received: from mx2.suse.de ([195.135.220.15]:37836 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732556AbeKWDpY (ORCPT ); Thu, 22 Nov 2018 22:45:24 -0500 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 9D599AE4A; Thu, 22 Nov 2018 17:05:03 +0000 (UTC) Subject: Re: [PATCH 4/4] mm: Stall movable allocations until kswapd progresses during serious external fragmentation event To: Mel Gorman , Linux-MM Cc: Andrew Morton , David Rientjes , Andrea Arcangeli , Zi Yan , Michal Hocko , LKML References: <20181121101414.21301-1-mgorman@techsingularity.net> <20181121101414.21301-5-mgorman@techsingularity.net> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSFWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmNvbT7CwZcEEwEKAEECGwMFCwkIBwMFFQoJCAsFFgIDAQAC HgECF4ACGQEWIQSpQNQ0mSwujpkQPVAiT6fnzIKmZAUCWi/zTwUJBbOLuQAKCRAiT6fnzIKm ZIpED/4jRN/6LKZZIT4R2xoou0nJkBGVA3nfb+mUMgi3uwn/zC+o6jjc3ShmP0LQ0cdeuSt/ t2ytstnuARTFVqZT4/IYzZgBsLM8ODFY5vGfPw00tsZMIfFuVPQX3xs0XgLEHw7/1ZCVyJVr mTzYmV3JruwhMdUvIzwoZ/LXjPiEx1MRdUQYHAWwUfsl8lUZeu2QShL3KubR1eH6lUWN2M7t VcokLsnGg4LTajZzZfq2NqCKEQMY3JkAmOu/ooPTrfHCJYMF/5dpi8YF1CkQF/PVbnYbPUuh dRM0m3NzPtn5DdyfFltJ7fobGR039+zoCo6dFF9fPltwcyLlt1gaItfX5yNbOjX3aJSHY2Vc A5T+XAVC2sCwj0lHvgGDz/dTsMM9Ob/6rRJANlJPRWGYk3WVWnbgW8UejCWtn1FkiY/L/4qJ UsqkId8NkkVdVAenCcHQmOGjRQYTpe6Cf4aQ4HGNDeWEm3H8Uq9vmHhXXcPLkxBLRbGDSHyq vUBVaK+dAwAsXn/5PlGxw1cWtur1ep7RDgG3vVQDhIOpAXAg6HULjcbWpBEFaoH720oyGmO5 kV+yHciYO3nPzz/CZJzP5Ki7Q1zqBb/U6gib2at5Ycvews+vTueYO+rOb9sfD8BFTK386LUK uce7E38owtgo/V2GV4LMWqVOy1xtCB6OAUfnGDU2EM7ATQRbGTU1AQgAn0H6UrFiWcovkh6E XVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQLa1PQDUi6j00ChlcR66g9/V0sPIcSutacPKf dKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMhFmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCT sTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sfbAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZO rIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq+aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahK tQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4njQARAQABwsF8BBgBCgAmFiEEqUDUNJksLo6Z ED1QIk+n58yCpmQFAlsZNTUCGwwFCQPCZwAACgkQIk+n58yCpmQ83g/9Frg1sRMdGPn98zV+ O2eC3h0p5f/oxxQ8MhG5znwHoW4JDG2TuxfcQuz7X7Dd5JWscjlw4VFJ2DD+IrDAGLHwPhCr RyfKalnrbYokvbClM9EuU1oUuh7k+Sg5ECNXEsamW9AiWGCaKWNDdHre3Lf4xl+RJWxghOVW RiUdpLA/a3yDvJNVr6rxkDHQ1P24ZZz/VKDyP+6g8aty2aWEU0YFNjI+rqYZb2OppDx6fdma YnLDcIfDFnkVlDmpznnGCyEqLLyMS3GH52AH13zMT9L9QYgT303+r6QQpKBIxAwn8Jg8dAlV OLhgeHXKr+pOQdFf6iu2sXlUR4MkO/5KWM1K0jFR2ug8Pb3aKOhowVMBT64G0TXhQ/kX4tZ2 ZF0QZLUCHU3Cigvbu4AWWVMNDEOGD/4sn9OoHxm6J04jLUHFUpFKDcjab4NRNWoHLsuLGjve Gdbr2RKO2oJ5qZj81K7os0/5vTAA4qHDP2EETAQcunTn6aPlkUnJ8aw6I1Rwyg7/XsU7gQHF IM/cUMuWWm7OUUPtJeR8loxZiZciU7SMvN1/B9ycPMFs/A6EEzyG+2zKryWry8k7G/pcPrFx O2PkDPy3YmN1RfpIX2HEmnCEFTTCsKgYORangFu/qOcXvM83N+2viXxG4mjLAMiIml1o2lKV cqmP8roqufIAj+Ohhzs= Message-ID: <35ea6691-e819-5581-7d32-39c1abfbe775@suse.cz> Date: Thu, 22 Nov 2018 18:02:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181121101414.21301-5-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/18 11:14 AM, Mel Gorman wrote: > An event that potentially causes external fragmentation problems has > already been described but there are degrees of severity. A "serious" > event is defined as one that steals a contiguous range of pages of an order > lower than fragment_stall_order (PAGE_ALLOC_COSTLY_ORDER by default). If a > movable allocation request that is allowed to sleep needs to steal a small > block then it schedules until kswapd makes progress or a timeout passes. > The watermarks are also boosted slightly faster so that kswapd makes > greater effort to reclaim enough pages to avoid the fragmentation event. > > This stall is not guaranteed to avoid serious fragmentation events. > If memory pressure is high enough, the pages freed by kswapd may be > reallocated or the free pages may not be in pageblocks that contain > only movable pages. Furthermore an allocation request that cannot stall > (e.g. atomic allocations) or unmovable/reclaimable allocations will still > proceed without stalling. Not doing this for unmovable/reclaimable allocations is kinda disadvantage? > ============================================================== > > +fragment_stall_order > + > +External fragmentation control is managed on a pageblock level where the > +page allocator tries to avoid mixing pages of different mobility within page > +blocks (e.g. order 9 on 64-bit x86). If external fragmentation is perfectly > +controlled then a THP allocation will often succeed up to the number of > +movable pageblocks in the system as reported by /proc/pagetypeinfo. > + > +When memory is low, the system may have to mix pageblocks and will wake > +kswapd to try control future fragmentation. fragment_stall_order controls if > +the allocating task will stall if possible until kswapd makes some progress > +in preference to fragmenting the system. This incurs a small stall penalty > +in exchange for future success at allocating huge pages. If the stalls > +are undesirable and high-order allocations are irrelevant then this can > +be disabled by writing 0 to the tunable. Writing the pageblock order will > +strongly (but not perfectly) control external fragmentation. > + > +The default will stall for fragmenting allocations smaller than the > +PAGE_ALLOC_COSTLY_ORDER (defined as order-3 at the time of writing). Perhaps be more explicit that steals of orders strictly lower than given value will stall? So for the default order-3, the sysctl value is 4, which might confuse somebody. > + > @@ -2130,9 +2131,10 @@ static bool can_steal_fallback(unsigned int order, int start_mt) > return false; > } > > + > +static void stall_fragmentation(struct zone *pzone) > +{ > + DEFINE_WAIT(wait); > + long remaining = 0; > + long timeout = HZ/50; > + pg_data_t *pgdat = pzone->zone_pgdat; > + > + if (current->flags & PF_MEMALLOC) > + return; > + > + boost_watermark(pzone, true); Should zone->lock be taken around this to make watermark_boost adjustment safe? Similar to balance_pgdat(). > + prepare_to_wait(&pgdat->pfmemalloc_wait, &wait, TASK_INTERRUPTIBLE); > + if (waitqueue_active(&pgdat->kswapd_wait)) > + wake_up_interruptible(&pgdat->kswapd_wait); > + remaining = schedule_timeout(timeout); > + finish_wait(&pgdat->pfmemalloc_wait, &wait); > + if (remaining != timeout) { > + trace_mm_fragmentation_stall(pgdat->node_id, > + jiffies_to_usecs(timeout - remaining)); > + count_vm_event(FRAGMENTSTALL); > + } > } > > @@ -4186,6 +4234,14 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > */ > alloc_flags = gfp_to_alloc_flags(gfp_mask); > > + /* > + * Consider stalling on heavy for movable allocations in preference to > + * fragmenting unmovable/reclaimable pageblocks. > + */ > + if ((gfp_mask & (__GFP_MOVABLE|__GFP_DIRECT_RECLAIM)) == > + (__GFP_MOVABLE|__GFP_DIRECT_RECLAIM)) > + alloc_flags |= ALLOC_FRAGMENT_STALL; Surprised that this only has effect in the slowpath, i.e. when watermarks are below 'low'. If it's intended (to not stall that much I suppose) maybe explain the rationale in the changelog? Thanks for the series, Mel, hope the results are still optimistic after some of the fixes that might unfortunately limit its impact :) Vlastimil