linux-kernel - Re: [PATCH v2 00/13] forcealign for xfs

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Message-ID: <e2799d3e-734e-4909-ba90-931799ef486a@oracle.com>
Date: Mon, 8 Jul 2024 08:48:19 +0100
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: chandan.babu@...cle.com, djwong@...nel.org, dchinner@...hat.com,
        viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, catherine.hoang@...cle.com,
        martin.petersen@...cle.com
Subject: Re: [PATCH v2 00/13] forcealign for xfs

On 06/07/2024 08:53, Christoph Hellwig wrote:
> On Fri, Jul 05, 2024 at 04:24:37PM +0000, John Garry wrote:
>> The actual forcealign patches are the same in this series, modulo an
>> attempt for a fix in xfs_bunmapi_align().
>>
>> Why forcealign?
>> In some scenarios to may be required to guarantee extent alignment and
>> granularity.
>>
>> For example, for atomic writes, the maximum atomic write unit size would
>> be limited at the extent alignment and granularity, guaranteeing that an
>> atomic write would not span data present in multiple extents.
>>
>> forcealign may be useful as a performance tuning optimization in other
>> scenarios.
> 
>  From previous side discussion I know Dave disagrees, but given how
> much pain the larger than FSB rtextents have caused I'm very skeptical
> if taking this on is the right tradeoff.
> 

I am not sure what that pain is, but I guess it's the maintainability 
and scalability of the scattered "if RT" checks for rounding up and down 
to larger extent size, right?

For forcealign, at least we can factor that stuff mostly into common 
forcealign+RT helpers, to keep the checks common. That is apart from the 
block allocator code.
>