linux-kernel - Re: [GIT PULL] vfs dio

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Message-ID: <Z5nL-NOQrAlaWNjy@infradead.org>
Date: Tue, 28 Jan 2025 22:34:32 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] vfs dio

[Sorry for the delay, I've been distrracted by a fun mix of personal
business and urgend customer work]

On Mon, Jan 20, 2025 at 11:24:56AM -0800, Linus Torvalds wrote:
> On Sat, 18 Jan 2025 at 05:09, Christian Brauner <brauner@...nel.org> wrote:
> >
> > Add a separate dio read align field to statx, as many out of place write
> > file systems can easily do reads aligned to the device sector size, but
> > require bigger alignment for writes.
> 
> I've pulled this, but it needs some fixing.
> 
> You added the 'dio_read_offset_align' field to 'struct kstat', and
> that structure is *critical*, because it's used even for the real
> 'stat()' calls that people actually use (as opposed to the statx side
> that is seldom a real issue).
> 
> And that field was added in a way that causes the struct to grow due
> to alignment issues.  For no good reason, because there were existing
> holes in there.

Indeed, sorry.  I put all attention on the user visible struct statx
and missed optimizing the in-kernel kstat.

> I despise the whole statx thing exactly because it has (approximately)
> five specialized users, while slowing down regular stat/fstat that is
> used widely absolutely *evertwhere*.

Yeah.  I still hate the statx design as it overload the critical
stat information with all the misc based path information that is
useful in some cases but not actually needed for most.  Not much
we can do about that now, though.