linux-kernel - Re: [PATCH v5 09/10] xfs: Allow block allocator to take an alignment hint

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Message-ID: <4d9499e3-4698-4d0c-b7bb-104023b29f3a@oracle.com>
Date: Wed, 12 Mar 2025 08:05:14 +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 09/10] xfs: Allow block allocator to take an alignment
 hint

On 12/03/2025 07:42, Christoph Hellwig wrote:
>>   	else if (ap->datatype & XFS_ALLOC_USERDATA)
>>   		align = xfs_get_extsz_hint(ap->ip);
>> +
>> +	if (align > 1 && (ap->flags & XFS_BMAPI_EXTSZALIGN))
>> +		args->alignment = align;
>> +
> 
> Add a comment please.

ok

> 
>> +/* Try to align allocations to the extent size hint */
>> +#define XFS_BMAPI_EXTSZALIGN	(1u << 11)
> 
> Shouldn't we be doing this by default for any extent size hint
> based allocations?

I'm not sure.

I think that currently users just expect extszhint to hint at the 
granularity only.

Maybe users don't require alignment and adding an alignment requirement 
just leads to more fragmentation.

> 
>>   	bool			found;
>>   	bool			atomic_sw = flags & XFS_REFLINK_ATOMIC_SW;
>> +	uint32_t		bmapi_flags = XFS_BMAPI_COWFORK |
>> +					      XFS_BMAPI_PREALLOC;
>> +
>> +	if (atomic_sw)
>> +		bmapi_flags |= XFS_BMAPI_EXTSZALIGN;
> 
> Please add a comment why you are doing this.
> 

Sure

Thanks,
John