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Mon, 21 Jul 2025 13:36:51 +0200 Message-ID: <85946346-8bfd-4164-a49d-594b4a158588@gmx.com> Date: Mon, 21 Jul 2025 21:06:38 +0930 Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Compressed files & the page cache To: Jan Kara , Gao Xiang Cc: Barry Song <21cnbao@gmail.com>, Matthew Wilcox , Chris Mason , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org, Nicolas Pitre , Gao Xiang , Chao Yu , linux-erofs@lists.ozlabs.org, Jaegeuk Kim , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, David Woodhouse , Richard Weinberger , linux-mtd@lists.infradead.org, David Howells , netfs@lists.linux.dev, Paulo Alcantara , Konstantin Komarov , ntfs3@lists.linux.dev, Steve French , linux-cifs@vger.kernel.org, Phillip Lougher , Hailong Liu References: <7ea73f49-df4b-4f88-8b23-c917b4a9bd8a@linux.alibaba.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; 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While I agree with your point, >>> I have a slightly different perspective =E2=80=94 enabling large folio= s for >>> those devices might be beneficial, but the maximum order should >>> remain small. I'm referring to "small" large folios. >> >> Yeah, agreed. Having a way to limit the maximum order for those small >> devices (rather than disabling it completely) would be helpful. At >> least "small" large folios could still provide benefits when memory >> pressure is light. >=20 > Well, in the page cache you can tune not only the minimum but also the > maximum order of a folio being allocated for each inode. Btrfs and ext4 > already use this functionality. So in principle the functionality is the= re, > it is "just" a question of proper user interfaces or automatic logic to > tune this limit. >=20 > Honza And enabling large folios doesn't mean all fs operations will grab an=20 unnecessarily large folio. For buffered write, all those filesystem will only try to get folios as=20 large as necessary, not overly large. This means if the user space program is always doing buffered IO in a=20 power-of-two unit (and aligned offset of course), the folio size will=20 match the buffer size perfectly (if we have enough memory). So for properly aligned buffered writes, large folios won't really cause= =20 unnecessarily large folios, meanwhile brings all the benefits. Although I'm not familiar enough with filemap to comment on folio read=20 and readahead... Thanks, Qu