linux-kernel - Re: [PATCH v5 03/10] xfs: Refactor xfs_reflink_end_cow

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Message-ID: <589f2ce0-2fd8-47f6-bbd3-28705e306b68@oracle.com>
Date: Wed, 12 Mar 2025 08:27:05 +0000
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: brauner@...nel.org, djwong@...nel.org, cem@...nel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
        ritesh.list@...il.com, martin.petersen@...cle.com
Subject: Re: [PATCH v5 03/10] xfs: Refactor xfs_reflink_end_cow_extent()

On 12/03/2025 07:24, Christoph Hellwig wrote:
> On Mon, Mar 10, 2025 at 06:39:39PM +0000, John Garry wrote:
>> Refactor xfs_reflink_end_cow_extent() into separate parts which process
>> the CoW range and commit the transaction.
>>
>> This refactoring will be used in future for when it is required to commit
>> a range of extents as a single transaction, similar to how it was done
>> pre-commit d6f215f359637.
> 
> Darrick pointed out that if you do more than just a tiny number
> of extents per transactions you run out of log reservations very
> quickly here:
> 
> https://urldefense.com/v3/__https://lore.kernel.org/all/20240329162936.GI6390@frogsfrogsfrogs/__;!!ACWV5N9M2RV99hQ!PWLcBof1tKimKUObvCj4vOhljWjFmjtzVHLx9apcU5Rah1xZnmp_3PIq6eSwx6TdEXzMLYYyBfmZLgvj$
> 
> how does your scheme deal with that?
> 
The resblks calculation in xfs_reflink_end_atomic_cow() takes care of 
this, right? Or does the log reservation have a hard size limit, 
regardless of that calculation?

Thanks,
John