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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pwaKx8X1ahf/f+kUWCkPOV0SH985FU13FHH0XDHIhcibepRoAQglwQ+AingOuHCt+ hexL80g9HbmCscfsbE9u/hmukg1wVvvFNNxoGr1EG/sc2a+CvnE3x1Cr684W/7AMt0 h97vxN4soL/QFx4qs1xSAhkzh2f5VB2n6TYMKW0A= Date: Mon, 6 Nov 2023 10:26:35 -0800 From: Andrew Morton To: Stefan Roesch Cc: kernel-team@fb.com, hannes@cmpxchg.org, riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v1] mm: Fix for negative counter: nr_file_hugepages Message-Id: <20231106102635.55bdf0cd99baad5c1fc8617a@linux-foundation.org> In-Reply-To: <20231106181918.1091043-1-shr@devkernel.io> References: <20231106181918.1091043-1-shr@devkernel.io> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8E3CC180003 X-Stat-Signature: hs11huoya3f6s4a9zqqursrrzhcxs6xx X-Rspam-User: X-HE-Tag: 1699295197-26685 X-HE-Meta: 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 BSFZLB5o c5g8HiaHvLZwL0kw5RtM4NHkP4pB/DtcFGMeHyx6W8u39E0uxE86yWNqefmwjS31G1OEeCnUjF4Qr5LnQiIid85cyDi14W/WSXleC4MqKc9rMS/yvxiY9KJeysBYllrXe/jUL5KIs6k7Bc7jUhxfwmUNzShU4PybDaI3107vi3Sz3lQH0KEeJKzduBbCwGCOI9FnXGAT3mK2L01nRJLUpgHZJ4oZypMUInf5W7HknhOh8Vf3FpyA38AmO1sVQmH45RPsgRAvxll5KbUg/zV2RWRKDpCKelOl0i9sOfR4nV9m6JHU= 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 Mon, 6 Nov 2023 10:19:18 -0800 Stefan Roesch wrote: > While qualifiying the 6.4 release, the following warning was detected in > messages: > > vmstat_refresh: nr_file_hugepages -15664 > > The warning is caused by the incorrect updating of the NR_FILE_THPS > counter in the function split_huge_page_to_list. The if case is checking > for folio_test_swapbacked, but the else case is missing the check for > folio_test_pmd_mappable. The other functions that manipulate the counter > like __filemap_add_folio and filemap_unaccount_folio have the > corresponding check. > > I have a test case, which reproduces the problem. It can be found here: > https://github.com/sroeschus/testcase/blob/main/vmstat_refresh/madv.c > > The test case reproduces on an XFS filesystem. Running the same test > case on a BTRFS filesystem does not reproduce the problem. > > AFAIK version 6.1 until 6.6 are affected by this problem. I'm thinking a cc:stable is justified. > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2740,7 +2740,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > if (folio_test_swapbacked(folio)) { > __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, > -nr); > - } else { > + } else if (folio_test_pmd_mappable(folio)) { > + > __lruvec_stat_mod_folio(folio, NR_FILE_THPS, > -nr); > filemap_nr_thps_dec(mapping); > I expect this will backport OK until it hits 3e9a13daa ("huge_memory: convert split_huge_page_to_list() to use a folio") at which point the -stable maintainers might request a reworked version.