Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt

Christoph Hellwig
2025-03-20T14:12:07Z

On Thu, Mar 20, 2025 at 09:19:40AM +0000, John Garry wrote:
> But is there value in reporting this limit? I am not sure. I am not sure
> what the user would do with this info.

Align their data structures to it, e.g. size the log buffers to it.

> Maybe, for example, they want to write 1K consecutive 16K pages, each
> atomically, and decide to do a big 16M atomic write but find that it is
> slow as bdev atomic limit is < 16M.
>
> Maybe I should just update the documentation to mention that for XFS they
> should check the mounted bdev atomic limits.

For something working on files having to figure out the underlying
block device (which is non-trivial given the various methods of
multi-device support) and then looking into block sysfs is a no-go.

So if we have any sort of use case for it we should expose the limit.