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Fri, 08 Nov 2024 11:39:49 -0800 (PST) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e99a348dd6sm6081261a91.0.2024.11.08.11.39.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Nov 2024 11:39:49 -0800 (PST) Message-ID: <75bf5237-efc4-4fb7-9e24-061354bff9ac@kernel.dk> Date: Fri, 8 Nov 2024 12:39:48 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/13] mm: add PG_uncached page flag To: "Kirill A. Shutemov" Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org References: <20241108174505.1214230-1-axboe@kernel.dk> <20241108174505.1214230-4-axboe@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: o6zepz94ryyzixbof8ycdiggj6dupkkd X-Rspam-User: X-Rspamd-Queue-Id: 1D87510001E X-Rspamd-Server: rspam02 X-HE-Tag: 1731094720-680692 X-HE-Meta: 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 r1btnLYU qONLRGYgwo4hKjK0WUw3UAFR1hZmOIx9ptmQxVWv9aKaGqDLGd/r/lJQLUMUzAqSdkHF0lD1UhhZvkM33YQFbhD2GR+xYHpqrMOX4gStkDurh5kES/KfQB2If1ximquMYLfsN/nTHNhCQWGqiVxUQ3djgDhGA7YvWjELxebuqhfvtw5GyGOz8UthqNcrewvf0mjkqVm/H8YkSXpM1Q5Ow7Olhn3uJ1YP9EyM7Uw3b4ExsVjODSitxpdoS7aidvCK6WhhCsCYof6hFQYFIfQDEXKBO47tSMfXHEqsj19aNh1/sVq3q1WMXMN9r2C2d9BNRqgwj86d08bSQIrY6ePpYFAOmG2cF2HJxUK1fpI4OdR+t+njB6gr6KaLz4DS/oAcAsCY6S5el6caEaEOjaceY2jAYqA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000017, 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 11/8/24 12:25 PM, Kirill A. Shutemov wrote: > On Fri, Nov 08, 2024 at 10:43:26AM -0700, Jens Axboe wrote: >> Add a page flag that file IO can use to indicate that the IO being done >> is uncached, as in it should not persist in the page cache after the IO >> has been completed. > > Flag bits are precious resource. It would be nice to re-use an existing > bit if possible. I knoew, like I mentioned in the reply to willy, I knew this one would be an interesting discussion in and of itself. > PG_reclaim description looks suspiciously close to what you want. > I wounder if it would be valid to re-define PG_reclaim behaviour to drop > the page after writeback instead of moving to the tail of inactive list. You're the mm expert - I added the flag since then it has a clearly defined meaning, and I would not need to worry about any kind of odd overlap in paths I didn't know about. Would definitely entertain reusing something else, but I'll leave that in the hands of the people that know this code and the various intricacies and assumptions a lot better than I do. -- Jens Axboe