From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id D81086B0038 for ; Mon, 20 Feb 2017 11:34:27 -0500 (EST) Received: by mail-wr0-f200.google.com with SMTP id n39so7902599wrn.0 for ; Mon, 20 Feb 2017 08:34:27 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z64si586747wrc.201.2017.02.20.08.34.26 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 20 Feb 2017 08:34:26 -0800 (PST) Subject: Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx References: <20170215092247.15989-1-mgorman@techsingularity.net> <20170215092247.15989-4-mgorman@techsingularity.net> <001501d2881d$242aa790$6c7ff6b0$@alibaba-inc.com> <20170216081039.ukbxl2b4khnwwbic@techsingularity.net> <001f01d2882d$9dd14850$d973d8f0$@alibaba-inc.com> From: Vlastimil Babka Message-ID: Date: Mon, 20 Feb 2017 17:34:21 +0100 MIME-Version: 1.0 In-Reply-To: <001f01d2882d$9dd14850$d973d8f0$@alibaba-inc.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hillf Danton , 'Mel Gorman' Cc: 'Andrew Morton' , 'Shantanu Goel' , 'Chris Mason' , 'Johannes Weiner' , 'LKML' , 'Linux-MM' On 02/16/2017 09:21 AM, Hillf Danton wrote: > > On February 16, 2017 4:11 PM Mel Gorman wrote: >> On Thu, Feb 16, 2017 at 02:23:08PM +0800, Hillf Danton wrote: >> > On February 15, 2017 5:23 PM Mel Gorman wrote: >> > > */ >> > > static int kswapd(void *p) >> > > { >> > > - unsigned int alloc_order, reclaim_order, classzone_idx; >> > > + unsigned int alloc_order, reclaim_order; >> > > + unsigned int classzone_idx = MAX_NR_ZONES - 1; >> > > pg_data_t *pgdat = (pg_data_t*)p; >> > > struct task_struct *tsk = current; >> > > >> > > @@ -3447,20 +3466,23 @@ static int kswapd(void *p) >> > > tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; >> > > set_freezable(); >> > > >> > > - pgdat->kswapd_order = alloc_order = reclaim_order = 0; >> > > - pgdat->kswapd_classzone_idx = classzone_idx = 0; >> > > + pgdat->kswapd_order = 0; >> > > + pgdat->kswapd_classzone_idx = MAX_NR_ZONES; >> > > for ( ; ; ) { >> > > bool ret; >> > > >> > > + alloc_order = reclaim_order = pgdat->kswapd_order; >> > > + classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); >> > > + >> > > kswapd_try_sleep: >> > > kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order, >> > > classzone_idx); >> > > >> > > /* Read the new order and classzone_idx */ >> > > alloc_order = reclaim_order = pgdat->kswapd_order; >> > > - classzone_idx = pgdat->kswapd_classzone_idx; >> > > + classzone_idx = kswapd_classzone_idx(pgdat, 0); >> > > pgdat->kswapd_order = 0; >> > > - pgdat->kswapd_classzone_idx = 0; >> > > + pgdat->kswapd_classzone_idx = MAX_NR_ZONES; >> > > >> > > ret = try_to_freeze(); >> > > if (kthread_should_stop()) >> > > @@ -3486,9 +3508,6 @@ static int kswapd(void *p) >> > > reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx); >> > > if (reclaim_order < alloc_order) >> > > goto kswapd_try_sleep; >> > >> > If we fail order-5 request, can we then give up order-5, and >> > try order-3 if requested, after napping? >> > >> >> That has no bearing upon this patch. At this point, kswapd has stopped >> reclaiming at the requested order and is preparing to sleep. If there is >> a parallel request for order-3 while it's sleeping, it'll wake and start >> reclaiming at order-3 as requested. >> > Right, but the order-3 request can also come up while kswapd is active and > gives up order-5. "Giving up on order-5" means it will set sc.order to 0, go to sleep (assuming order-0 watermarks are OK) and wakeup kcompactd for order-5. There's no way how kswapd could help an order-3 allocation at that point - it's up to kcompactd. > thanks > Hillf > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org