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=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 EE38EC433DF for ; Tue, 9 Jun 2020 12:28:16 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B04AF207ED for ; Tue, 9 Jun 2020 12:28:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B04AF207ED Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 449AD6B0002; Tue, 9 Jun 2020 08:28:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3FB746B0005; Tue, 9 Jun 2020 08:28:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3120D6B0006; Tue, 9 Jun 2020 08:28:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0152.hostedemail.com [216.40.44.152]) by kanga.kvack.org (Postfix) with ESMTP id 177556B0002 for ; Tue, 9 Jun 2020 08:28:16 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id C9801180E4821 for ; Tue, 9 Jun 2020 12:28:15 +0000 (UTC) X-FDA: 76909600950.17.hill19_340349226dc2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin17.hostedemail.com (Postfix) with ESMTP id 9B555180D6D50 for ; Tue, 9 Jun 2020 12:28:15 +0000 (UTC) X-HE-Tag: hill19_340349226dc2 X-Filterd-Recvd-Size: 6401 Received: from outbound-smtp04.blacknight.com (outbound-smtp04.blacknight.com [81.17.249.35]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Tue, 9 Jun 2020 12:28:14 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp04.blacknight.com (Postfix) with ESMTPS id 50EFDBEEBF 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) X-Rspamd-Queue-Id: 9B555180D6D50 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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