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Message-ID: <20250506054722.GA28781@lst.de> Date: Tue, 6 May 2025 07:47:22 +0200 From: Christoph Hellwig <hch@....de> To: "Darrick J. Wong" <djwong@...nel.org> Cc: Christoph Hellwig <hch@....de>, Zhang Yi <yi.zhang@...weicloud.com>, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-block@...r.kernel.org, dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, tytso@....edu, john.g.garry@...cle.com, bmarzins@...hat.com, chaitanyak@...dia.com, shinichiro.kawasaki@....com, brauner@...nel.org, yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com Subject: Re: [RFC PATCH v4 07/11] fs: statx add write zeroes unmap attribute On Mon, May 05, 2025 at 10:36:54PM -0700, Darrick J. Wong wrote: > I think STATX_* (i.e. not STATX_ATTR_*) flags have two purposes: 1) to > declare that specific fields in struct statx actually have meaning, most > notably in scenarios where zeroes are valid field contents; and 2) if > filling out the field is expensive, userspace can elect not to have it > filled by leaving the bit unset. I don't know how userspace is supposed > to figure out which fields are expensive. Yes. > (I'm confused about the whole premise of /this/ patch -- it's a "fast > zeroing" fallocate flag that causes the *device* to unmap, so that the > filesystem can preallocate and avoid unwritten extent conversions? Yes. > What happens if the block device is thinp and it runs out of space? > That seems antithetical to fallocate...) While the origin posix_fallocate was about space preallocatіon, these days fallocate seems to be more about extent layout and/or fast zeroing. I'm not a huge fan of either this or the hardware atomics as they force a FTL layer world view which is quite ingrained but also rather stupid, but some folks really want to go down there full throttle, so..
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