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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 058EAC433EF for ; Thu, 19 May 2022 12:26:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 920078D0001; Thu, 19 May 2022 08:26:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8A9A96B0074; Thu, 19 May 2022 08:26:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6FDD68D0001; Thu, 19 May 2022 08:26:12 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 5C0CA6B0073 for ; Thu, 19 May 2022 08:26:12 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 2CDF23350E for ; Thu, 19 May 2022 12:26:12 +0000 (UTC) X-FDA: 79482414984.20.B4727BC Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf21.hostedemail.com (Postfix) with ESMTP id 5C60B1C00C9 for ; Thu, 19 May 2022 12:26:01 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 1535F1FA1F; Thu, 19 May 2022 12:26:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1652963170; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=St4z8AfblGmvqzbUxJh1IMUZIs7c2S6glVT6K7wgV4Y=; b=RjJKfoRagOlZSNpaiRvHF5ajP1C1v5f0dHqiQQl3CtxeyUeMpfazEqgeuMbyTevJUO/EHx Ojbjf/18KOESz5qkLkrSruIJvnRQTbR2RxZ/vtWhcdrju1QXzFhByFvz4Yzq8QiORYftbk 4pBlCbNcSU1AEH2yrtZczn4d/+ATFV0= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1652963170; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=St4z8AfblGmvqzbUxJh1IMUZIs7c2S6glVT6K7wgV4Y=; b=51harBtCuZH/JcSw6uOuRESvg0/5o13Bes9SXTjVcPgFPS8vIU0vQgBB0Wv34UJ4uTeKUC ewbR+s9FsPZQ+UAA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id DD63613456; Thu, 19 May 2022 12:26:09 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id xcHeNGE3hmJYBwAAMHmgww (envelope-from ); Thu, 19 May 2022 12:26:09 +0000 Message-ID: <1b478a71-7de1-2097-7006-634d51f3fda1@suse.cz> Date: Thu, 19 May 2022 14:26:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH 4/6] mm/page_alloc: Remove unnecessary page == NULL check in rmqueue Content-Language: en-US To: Mel Gorman Cc: Andrew Morton , Nicolas Saenz Julienne , Marcelo Tosatti , Michal Hocko , LKML , Linux-MM References: <20220512085043.5234-1-mgorman@techsingularity.net> <20220512085043.5234-5-mgorman@techsingularity.net> <5a0c9b7c-3620-3e0f-7510-d0fc3fa6ceda@suse.cz> <20220519121341.GV3441@techsingularity.net> From: Vlastimil Babka In-Reply-To: <20220519121341.GV3441@techsingularity.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5C60B1C00C9 Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=RjJKfoRa; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=51harBtC; spf=pass (imf21.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspam-User: X-Stat-Signature: sxg6wtgcmmf6bsj8pcz5ou8p693hxzhm X-HE-Tag: 1652963161-554441 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 5/19/22 14:13, Mel Gorman wrote: > On Thu, May 19, 2022 at 12:57:01PM +0200, Vlastimil Babka wrote: >> On 5/12/22 10:50, Mel Gorman wrote: >>> The VM_BUG_ON check for a valid page can be avoided with a simple >>> change in the flow. The ZONE_BOOSTED_WATERMARK is unlikely in general >>> and even more unlikely if the page allocation failed so mark the >>> branch unlikely. >> >> Hm, so that makes a DEBUG_VM config avoid the check. On the other hand, >> it puts it on the path returning from rmqueue_pcplist() for all configs, >> and that should be the fast path. So unless things further change in the >> following patches, it doesn't seem that useful? >> > > You're right -- the fast path ends up with both a if > (page) and if (!page) checks. Andrew, can you drop the patch > mm-page_alloc-remove-unnecessary-page-==-null-check-in-rmqueue.patch from > your tree please? > > Originally the flow was important when I was writing the patch and later > became unnecessary. However, it reminded me of another problem I thought > of when writing this and then forgotten to note it in the changelog. If > the page allocation fails then ZONE_BOOSTED_WATERMARK should still be > tested and cleared before waking kswapd. It could happen if an allocation > attempt tried to fallback to another migratetype and still fail to find > a suitable page. This is true whether going through the PCP lists or not. > > So what do you think of me adding this patch to a follow-up series? LGTM. > > --8<-- > mm/page_alloc: Remove mistaken page == NULL check in rmqueue > > If a page allocation fails, the ZONE_BOOSTER_WATERMARK should be tested, > cleared and kswapd woken whether the allocation attempt was via the PCP > or directly via the buddy list. > > Remove the page == NULL so the ZONE_BOOSTED_WATERMARK bit is checked > unconditionally. As it is unlikely that ZONE_BOOSTED_WATERMARK is set, > mark the branch accordingly. > > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka > --- > mm/page_alloc.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 1c4c54503a5d..61d5bc2efffe 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3765,12 +3765,10 @@ struct page *rmqueue(struct zone *preferred_zone, > > page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags, > migratetype); > - if (unlikely(!page)) > - return NULL; > > out: > /* Separate test+clear to avoid unnecessary atomics */ > - if (test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags)) { > + if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) { > clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags); > wakeup_kswapd(zone, 0, 0, zone_idx(zone)); > } >