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From: Dave Chinner <david@fromorbit.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Nikolay Borisov <nborisov@suse.com>,
	linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	djwong@kernel.org
Subject: Re: [PATCH] vfs: Optimize dedupe comparison
Date: Fri, 16 Jul 2021 08:33:52 +1000	[thread overview]
Message-ID: <20210715223352.GB219491@dread.disaster.area> (raw)
In-Reply-To: <YPBPkupPDnsCXrLU@casper.infradead.org>

On Thu, Jul 15, 2021 at 04:09:06PM +0100, Matthew Wilcox wrote:
> On Thu, Jul 15, 2021 at 05:44:15PM +0300, Nikolay Borisov wrote:
> > I was wondering the same thing, but AFAICS it seems to be possible i.e
> > if userspace spaces bad offsets, while all kinds of internal fs
> > synchronization ops are going to be performed on aligned offsets, that
> > doesn't mean the original ones, passed from userspace are themselves
> > aligned explicitly.
> 
> Ah, I thought it'd be failed before we got to this point.
> 
> But honestly, I think x86-64 needs to be fixed to either use
> __builtin_memcmp() or to have a nicely written custom memcmp().  I
> tried to find the gcc implementation of __builtin_memcmp() on
> x86-64, but I can't.

Yup, this. memcmp() is widley used in hot paths through all the
filesystem code and the rest of the kernel. We should fix the
generic infrastructure problem, not play whack-a-mole to with custom
one-off fixes that avoid the problem just where it shows up in some
profile...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  reply	other threads:[~2021-07-15 22:33 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 14:13 [PATCH] vfs: Optimize dedupe comparison Nikolay Borisov
2021-07-15 14:30 ` Matthew Wilcox
2021-07-15 14:44   ` Nikolay Borisov
2021-07-15 15:09     ` Matthew Wilcox
2021-07-15 22:33       ` Dave Chinner [this message]
2021-07-20 14:58         ` Nikolay Borisov
2021-07-20 15:12           ` Matthew Wilcox
2021-07-16 12:10       ` Nikolay Borisov

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