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

[John Garry]

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