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Fri, 4 Nov 2022 08:32:02 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id DMAxKwLOZGM5YQAAMHmgww (envelope-from ); Fri, 04 Nov 2022 08:32:02 +0000 Date: Fri, 4 Nov 2022 09:32:01 +0100 From: Michal Hocko To: Yang Shi Cc: zokeefe@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH 1/2] mm: khugepaged: allow page allocation fallback to eligible nodes Message-ID: References: <20221103213641.7296-1-shy828301@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221103213641.7296-1-shy828301@gmail.com> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667550724; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; 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dmarc=pass (policy=quarantine) header.from=suse.com X-Stat-Signature: 98dhwq5e5bx9tp8jwezfnwhijp3ccqnj X-HE-Tag: 1667550724-643819 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 Thu 03-11-22 14:36:40, Yang Shi wrote: [...] > So use nodemask to record the nodes which have the same hit record, the > hugepage allocation could fallback to those nodes. And remove > __GFP_THISNODE since it does disallow fallback. And if nodemask is > empty (no node is set), it means there is one single node has the most > hist record, the nodemask approach actually behaves like __GFP_THISNODE. > > Reported-by: syzbot+0044b22d177870ee974f@syzkaller.appspotmail.com > Suggested-by: Zach O'Keefe > Suggested-by: Michal Hocko > Signed-off-by: Yang Shi > --- > mm/khugepaged.c | 32 ++++++++++++++------------------ > 1 file changed, 14 insertions(+), 18 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index ea0d186bc9d4..572ce7dbf4b0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -97,8 +97,8 @@ struct collapse_control { > /* Num pages scanned per node */ > u32 node_load[MAX_NUMNODES]; > > - /* Last target selected in hpage_collapse_find_target_node() */ > - int last_target_node; > + /* nodemask for allocation fallback */ > + nodemask_t alloc_nmask; This will eat another 1k on the stack on most configurations (NODE_SHIFT=10). Along with 4k of node_load this is quite a lot even on shallow call chains like madvise resp. khugepaged. I would just add a follow up patch which changes both node_load and alloc_nmask to dynamically allocated objects. Other than that LGTM. I thought we want to keep __GFP_THISNODE but after a closer look it seems that this flag is not really compatible with nodemask after all. node_zonelist() will simply return a trivial zone list for a single (preferred node) so no fallback to other nodes is possible. My bad to not realize it earlier. -- Michal Hocko SUSE Labs