linux-kernel - Re: [PATCH] fs: optimise generic_write_check

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Message-ID: <YQ09NFOPz/K3sDV6@zeniv-ca.linux.org.uk>
Date:   Fri, 6 Aug 2021 13:46:28 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: optimise generic_write_check_limits()

On Fri, Aug 06, 2021 at 12:22:10PM +0100, Pavel Begunkov wrote:
> Even though ->s_maxbytes is used by generic_write_check_limits() only in
> case of O_LARGEFILE, the value is loaded unconditionally, which is heavy
> and takes 4 indirect loads. Optimise it by not touching ->s_maxbytes,
> if it's not going to be used.

Out of curiosity - how much of improvement have you actually seen on that?
I can't say I hate the patch, but I'd like to see the data...