Re: [PATCH v2 04/14] fs: xfs: Make file data allocations observe the 'forcealign' flag

[John Garry]

> > Please note in case missed, I am mandating extsize hint for forcealign needs
> > to be a power-of-2. It just makes life easier for all the sub-extent
> > zero'ing later on.
>
> That's fine - that will need to be documented in the xfsctl man
> page...
>
> > Also we need to enforce that the AG count to be compliant with the extsize
>                                        ^^^^^ size?

Yes

> > hint for forcealign; but since the extsize hint for forcealign needs to be
> > compliant with stripe unit, above, and stripe unit would be compliant wth AG
> > count (right?), then this would be a given.
>
> We already align AG size to stripe unit when a stripe unit is set,
> and ensure that we don't place all the AG headers on the same stripe
> unit.
>
> However, if there is no stripe unit we don't align the AG to
> anything. 


> So, yes, AG sizing by mkfs will need to ensure that all
> AGs are correctly aligned to the underlying storage (integer
> multiple of the max atomic write size, right?)...

right, this is really important

> > > More below....
> > >
> > > > +	} else {
> > > > +		args->alignment = 1;
> > > > +	}
> > >
> > > Just initialise the allocation args structure with a value of 1 like
> > > we already do?
> >
> > It was being done in this way to have just a single place where the value is
> > initialised. It can easily be kept as is.
>
> I'd prefer it as is, because then the value is always initialised
> correctly and we only override in the special cases....

ok

> > are you saying that low-space allocator can set args->alignment = 1 to be
> > explicit?
>
> Yes.

ok

Thanks,
John