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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id 3-20020a05600c22c300b003f31d44f0cbsm3489708wmg.29.2023.04.28.06.05.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Apr 2023 06:05:19 -0700 (PDT) Date: Fri, 28 Apr 2023 14:05:19 +0100 From: Lorenzo Stoakes To: Jan Kara Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Christoph Hellwig , David Hildenbrand Subject: Re: [PATCH] mm: Do not reclaim private data from pinned page Message-ID: References: <20230428124140.30166-1-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230428124140.30166-1-jack@suse.cz> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B53DBC001B X-Rspam-User: X-Stat-Signature: z6hmsn4pc4r17keyctb1gfjszmzb4ja7 X-HE-Tag: 1682687122-102462 X-HE-Meta: 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 DiQ7eMKw dfOx+HWU2LKQDMPdpvbnu+dzKUEGgSBwAESb4cp0XJ9vMyIK9awVOUbD7qMcXngDWD8N4svYd8kZfYwSbG8e/iOhHsJfCB+vUg3g6fhwG21PctOMGh34U72X+nrVFs8Fp2kOHg1Q5/l9uiz1aOcHCk+gM3BSXv7JsOJntiwcZLSEy8IOfw972oBe+8Tv6u3KYp2GPzeI66nG3BgzHb2s9mjMVYhsiTJBMCs82HJzcMqb7K/zUJrKFBLpJ7+cxBBvlrTGenJRVkIlciIpNvzxnudRTvxdqhnKw6/3p+G2BzJvyF7lweOu9WT1L5O31gZHrHOTZaxvl8HhVGH3EKUQQkqOxr1XbGbq9xk5x7/zv4HygQnZGCftuOXgFZ1DnIr/h6yrO2ta3Ywh0N1hs9LxShkG/rz37Hq7DPXPG4Odv3QhObXoj/dY180D7Zg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000034, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 28, 2023 at 02:41:40PM +0200, Jan Kara wrote: > If the page is pinned, there's no point in trying to reclaim it. > Furthermore if the page is from the page cache we don't want to reclaim > fs-private data from the page because the pinning process may be writing > to the page at any time and reclaiming fs private info on a dirty page > can upset the filesystem (see link below). > > Link: https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz > Signed-off-by: Jan Kara > --- > mm/vmscan.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > This was the non-controversial part of my series [1] dealing with pinned pages > in filesystems. It is already a win as it avoids crashes in the filesystem and > we can drop workarounds for this in ext4. Can we merge it please? > > [1] https://lore.kernel.org/all/20230209121046.25360-1-jack@suse.cz/ > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bf3eedf0209c..401a379ea99a 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1901,6 +1901,16 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > } > } > > + /* > + * Folio is unmapped now so it cannot be newly pinned anymore. > + * No point in trying to reclaim folio if it is pinned. > + * Furthermore we don't want to reclaim underlying fs metadata > + * if the folio is pinned and thus potentially modified by the > + * pinning process as that may upset the filesystem. > + */ > + if (folio_maybe_dma_pinned(folio)) > + goto activate_locked; > + > mapping = folio_mapping(folio); > if (folio_test_dirty(folio)) { > /* > -- > 2.35.3 > This seems very sensible and helps ameliorate problematic GUP/file interactions so this seems a no-brainer. Reviewed-by: Lorenzo Stoakes