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Date:   Sat, 1 Aug 2020 11:01:38 -0600
From:   Jens Axboe <>
To:     Matthew Wilcox <>,
        Pavel Begunkov <>
Cc:     Alexander Viro <>,,
Subject: Re: [PATCH] fs: optimise kiocb_set_rw_flags()

On 8/1/20 9:37 AM, Matthew Wilcox wrote:
> On Sat, Aug 01, 2020 at 01:36:33PM +0300, Pavel Begunkov wrote:
>> Use a local var to collect flags in kiocb_set_rw_flags(). That spares
>> some memory writes and allows to replace most of the jumps with MOVEcc.
>> Signed-off-by: Pavel Begunkov <>
> Reviewed-by: Matthew Wilcox (Oracle) <>
> If you want to improve the codegen here further, I would suggest that
> renumbering the IOCB flags to match the RWF flags would lead to better
> codegen (can't do it the other way around; RWF flags are userspace ABI,
> IOCB flags are not).  iocb_flags() probably doesn't get any worse because
> the IOCB_ flags don't have the same numbers as the O_ bits (which differ
> by arch anyway).

Yeah that's not a bad idea, would kill a lot of branches.

Jens Axboe

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