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Thu, 18 Dec 2025 16:21:34 -0800 (PST) Date: Fri, 19 Dec 2025 00:21:34 +0000 From: Wei Yang To: "David Hildenbrand (Red Hat)" Cc: Zi Yan , Bijan Tabatabai , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shivankg@amd.com, Baolin Wang , Hugh Dickins , Chris Li , Kairui Song Subject: Re: [PATCH] mm: Consider non-anon swap cache folios in folio_expected_ref_count() Message-ID: <20251219002134.uqgtnr43zz7vvvtd@master> Reply-To: Wei Yang References: <20251216200727.2360228-1-bijan311@gmail.com> <6b4cadb2-6246-48cc-9c76-64ba0a23198b@kernel.org> <0C218C18-916B-4BB0-8B37-AC82503E4AD9@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E383420002 X-Stat-Signature: nmbh3bz37k8e5116eym71f87j6apw3qm X-HE-Tag: 1766103696-857941 X-HE-Meta: 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 yXntdqnQ 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 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 Wed, Dec 17, 2025 at 02:04:16AM +0100, David Hildenbrand (Red Hat) wrote: >> > > >> > > I am not very familiar with the memory hot-(un)plug or swapping code, so >> > > I am not 100% certain if this patch actually solves the root of the >> > > problem. I believe the issue is from shmem folios, in which case I believe >> > > this patch is correct. However, I couldn't think of an easy way to confirm >> > > that the affected folios were from shmem. I guess it could be possible that >> > > the root cause could be from some bug where some anonymous pages do not >> > > return true to folio_test_anon(). I don't think that's the case, but >> > > figured the MM maintainers would have a better idea of what's going on. >> >> I am not sure about if shmem in swapcache causes the issue, since >> the above setup does not involve shmem. +Baolin and Hugh for some insight. > >We might just push out another unrelated shmem page to swap as we create >memory pressure in the system I think. > One trivial question: currently we only put anon/shmem folio in swapcache, right? >> >> But David also mentioned that in __read_swap_cache_async() there is a chance >> that anon folio in swapcache can have anon flag not set yet. +Chris and Kairui >> for more analysis. > >Right, when we swapin an anon folio and did not map it into the page table >yet. Likely we can trigger something similar when we proactively read a shmem >page from swap into the swapcache. > >So it's unclear "where" a swapcache page belongs to until we move it to its >owner (anon / shmem), which is also why I cannot judge easily from > >[ 49.641309] migrating pfn b12f25 failed ret:7 >[ 49.641310] page: refcount:2 mapcount:0 mapping:0000000033bd8fe2 >index:0x7f404d925 pfn:0xb12f25 >[ 49.641311] aops:swap_aops >[ 49.641313] flags: 0x300000000030508(uptodate|active|owner_priv_1|reclaim|swapbacked|node=0|zone=3) >[ 49.641314] raw: 0300000000030508 ffffed312c4bc908 ffffed312c4bc9c8 >0000000000000000 >[ 49.641315] raw: 00000007f404d925 00000000000c823b 00000002ffffffff >0000000000000000 >[ 49.641315] page dumped because: migration failure > >What exactly that was. > >It was certainly an order-0 folio. > >[...] > >> >> I agree with David. Acked-by: Zi Yan > >Thanks for the fast review :) > >-- >Cheers > >David -- Wei Yang Help you, Help me