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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764761337; bh=WjtABvSbCCnx3nvKrk1EoRHpHn4A/68rGFxZqC4DWH8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JBl22uYMsIHsC6F3gqtDORz+MxQxHSbBOAiSBo1Xft5RQQbGgt3u7NN+kTir6Jhkk 1HUyrOhbg05uTTWQcxEE9EYbUue+bgPPA7mfmLCUMfZveif40kflHpRUgwM/wAosio PgG/kwk5iUi8Ar0sDBuqBJ9di/dfWfJOxk/cY1Tq50T0/qJGq5xNylDoT+oKxIV468 ddp8ZlwxT6EqgkI1/HqJne4XnVOT5QB/sfBSHj25srM3QTFHVaG7EGbIVwyDUG0yIq 1xfKegT6U4o7SfaivnusJbg1MEk+T4PiTJ+apuAO/l9r9+yPH1+IIpvhaZ3vHl/LcD M4mcRafKFJmeQ== Message-ID: <036614fd-e588-402c-8eb3-770ee9187bbd@kernel.org> Date: Wed, 3 Dec 2025 12:28:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free To: Gregory Price Cc: Michal Hocko , Andrew Morton , Aboorva Devarajan , vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador , Juan Yescas References: <20251201060009.1420792-1-aboorvad@linux.ibm.com> <20251201094112.07eb1e588b6da2ee70c4641d@linux-foundation.org> <47a8b4d5-f4d2-4772-b1b2-ee96bc21e742@kernel.org> <9de2f7e2-a202-499d-8858-6936beb251d9@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 58A0518000F X-Stat-Signature: kx1bck9s9gxayc774r9zs376zn18ruwn X-Rspam-User: X-HE-Tag: 1764761338-163589 X-HE-Meta: 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 ZfORHXYg s9W8JYN+4h+1K1PbPKaMiv97GlFqlU8tqn/CfPPTfqRoMXOM2kTdXnjIfETy3Zl7oA6GDoyzfV1/0S1xmox7lRRXz7GxHl0mxDktCNSLeJJ8KIcNEmZtlyKVoAFUq1EVi/Eny+3kypItcSpiQOJVc8JcVTIalwQMY0qgkie+d01xQ+s1n6RM1RExkKriduPMvPosDcBEmatVDQWFbXt/sktwYoaOgHexLHP4VDoFm+ma9uElPcp5nmD67wlBLPisZWwn7M7HAgxYxswyeV7XmIYJ81KDVPw4WnmHMH2jJY2Hjpo/xCwTs0/tvTg== 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: List-Subscribe: List-Unsubscribe: On 12/3/25 10:23, Gregory Price wrote: > On Wed, Dec 03, 2025 at 10:08:55AM +0100, David Hildenbrand (Red Hat) wrote: >> On 12/3/25 10:02, Gregory Price wrote: >>> >>> My transient failure (although i'm not sure it was actually transient, i >>> killed it and retried after a few minutes and it succeeded immediately) >>> was on a ZONE_MOVABLE block. >> >> Okay, so that one should not bail out. Longterm pinnins must never end up on >> such memory, and if it happens, we have to identify why and fix it. >> >> We have this known problem of "stream of short-term pinnings" that can >> temporarily turn memory effectively unmovable. Juan will talk about that at >> LPC [1]. > > Nice, fun, good topic. Looking forward to Japan n_n > >> >> We have another set of problematic cases (vmsplice(), fuse) but I would >> assume that these are not the cases you are hitting. >> > > We do use fuse, but this system was relatively quiet when i tried this. > > We do have some proactive reclaim / demotion going on, but i don't think > it was that (see below). > >>> >>> Kind of suggested to me there was some bad condition the resolved once I >>> took a second to release the lock and try again. >> >> Hard to tell I'm afraid. Do you still have the dump_folio() calls we print >> when migration fails? >> > > What luck, I do! :D :) > And i just noticed it's the same page over and over > > [ 3404.119270] migrating pfn c06f176 failed ret:1 > [ 3404.129152] page: refcount:4 mapcount:0 mapping:0000000061ca20ba index:0xad28e5b pfn:0xc06f176 > [ 3404.148284] memcg:ffff88842e855000 > [ 3404.155834] aops:btree_aops ino:1 Small folio. Not GUP-pinned (FOLL_PIN, otherwise our refcount would be >= 1024. It could be ordinary GUP (FOLL_GET) e.g., from vmsplice or some older O_DIRECT user that was not converted to FOLL_PIN yet. But maybe it's just btrfs / something else that temporarily holds a folio reference. Given that this is from 6.13 ... hard to tell :) > [ 3404.163193] flags: 0x17ffff066c00420c(referenced|uptodate|workingset|private|node=1|zone=3|lastcpupid=0x1ffff) Neither dirty nor under writeback. -- Cheers David