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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 73274C433E1 for ; Tue, 9 Jun 2020 12:28:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59C3E207ED for ; Tue, 9 Jun 2020 12:28:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729423AbgFIM2P (ORCPT ); Tue, 9 Jun 2020 08:28:15 -0400 Received: from outbound-smtp18.blacknight.com ([46.22.139.245]:54191 "EHLO outbound-smtp18.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726903AbgFIM2P (ORCPT ); Tue, 9 Jun 2020 08:28:15 -0400 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp18.blacknight.com (Postfix) with ESMTPS id 512461C36B9 for ; Tue, 9 Jun 2020 13:28:13 +0100 (IST) Received: (qmail 9958 invoked from network); 9 Jun 2020 12:28:13 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.18.57]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 9 Jun 2020 12:28:13 -0000 Date: Tue, 9 Jun 2020 13:28:11 +0100 From: Mel Gorman To: Charan Teja Reddy Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vinmenon@codeaurora.org Subject: Re: [PATCH] mm, page_alloc: skip ->waternark_boost for atomic order-0 allocations Message-ID: <20200609122811.GK3127@techsingularity.net> References: <1589882284-21010-1-git-send-email-charante@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1589882284-21010-1-git-send-email-charante@codeaurora.org> 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 Tue, May 19, 2020 at 03:28:04PM +0530, Charan Teja Reddy wrote: > When boosting is enabled, it is observed that rate of atomic order-0 > allocation failures are high due to the fact that free levels in the > system are checked with ->watermark_boost offset. This is not a problem > for sleepable allocations but for atomic allocations which looks like > regression. > Are high-order allocations in general of interest to this platform? If not then a potential option is to simply disable boosting. The patch is still relevant but it's worth thinking about. > This problem is seen frequently on system setup of Android kernel > running on Snapdragon hardware with 4GB RAM size. When no extfrag event > occurred in the system, ->watermark_boost factor is zero, thus the > watermark configurations in the system are: > _watermark = ( > [WMARK_MIN] = 1272, --> ~5MB > [WMARK_LOW] = 9067, --> ~36MB > [WMARK_HIGH] = 9385), --> ~38MB > watermark_boost = 0 > > After launching some memory hungry applications in Android which can > cause extfrag events in the system to an extent that ->watermark_boost > can be set to max i.e. default boost factor makes it to 150% of high > watermark. > _watermark = ( > [WMARK_MIN] = 1272, --> ~5MB > [WMARK_LOW] = 9067, --> ~36MB > [WMARK_HIGH] = 9385), --> ~38MB > watermark_boost = 14077, -->~57MB > > With default system configuration, for an atomic order-0 allocation to > succeed, having free memory of ~2MB will suffice. But boosting makes > the min_wmark to ~61MB thus for an atomic order-0 allocation to be > successful system should have minimum of ~23MB of free memory(from > calculations of zone_watermark_ok(), min = 3/4(min/2)). But failures are > observed despite system is having ~20MB of free memory. In the testing, > this is reproducible as early as first 300secs since boot and with > furtherlowram configurations(<2GB) it is observed as early as first > 150secs since boot. > > These failures can be avoided by excluding the ->watermark_boost in > watermark caluculations for atomic order-0 allocations. > > Signed-off-by: Charan Teja Reddy > --- > mm/page_alloc.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d001d61..5193d7e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3709,6 +3709,18 @@ static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone) > } > > mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK); > + /* > + * Allow GFP_ATOMIC order-0 allocations to exclude the > + * zone->watermark_boost in its watermark calculations. > + * We rely on the ALLOC_ flags set for GFP_ATOMIC > + * requests in gfp_to_alloc_flags() for this. Reason not to > + * use the GFP_ATOMIC directly is that we want to fall back > + * to slow path thus wake up kswapd. > + */ The comment is a bit difficult to parse. Maybe this. /* * Ignore watermark boosting for GFP_ATOMIC order-0 allocations * when checking the min watermark. The min watermark is the * point where boosting is ignored so that kswapd is woken up * when below the low watermark. */ I left out the ALLOC_ part for reasons that are explained blow. > + if (unlikely(!order && !(alloc_flags & ALLOC_WMARK_MASK) && > + (alloc_flags & (ALLOC_HARDER | ALLOC_HIGH)))) { > + mark = zone->_watermark[WMARK_MIN]; > + } The second check is a bit more obscure than it needs to be and depends on WMARK_MIN == 0. That will probably be true forever but it's not obvious at a glance. I suggest something like ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN). For detecting atomic alloctions, you rely on the either ALLOC_HARDER or ALLOC_HIGH being set. ALLOC_HIGH can be set for non-atomic allocations and ALLOC_HARDER can be set for RT tasks. You probably should just test the gfp_mask because as it stands non-atomic allocations can ignore the boost too. Finally, the patch puts an unlikely check into a relatively fast path even though watermarks may be fine with or without boosting. Instead you could put the checks in zone_watermark_fast() if and only if the watermarks failed the first time. If the checks pass, the watermarks get checked a second time. This will be fractionally slower for requests failing watermark checks but there is no penalty for most allocation requests. It would need the gfp_mask to be passed into zone_watermark_fast but as it's an inlined function, there should be no cost to passing in the arguement i.e. do something like this at the end of zone_watermark_fast if (__zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags, free_pages)) return true; /* Ignore watermark boosting for .... */ if (unlikely(!order .....) { mark = ... return __zone_watermark_ok(...); } return false; -- Mel Gorman SUSE Labs