Re: [RFC] iomap: use huge zero folio in iomap_dio_zero

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On Thu, May 09, 2024 at 08:05:24AM -0700, Christoph Hellwig wrote:
> On Thu, May 09, 2024 at 07:32:50AM -0700, Darrick J. Wong wrote:
> > On Thu, May 09, 2024 at 05:58:23AM -0700, Christoph Hellwig wrote:
> > > On Thu, May 09, 2024 at 12:55:14PM +0000, Pankaj Raghav (Samsung) wrote:
> > > > We might still fail here during mount. My question is: do we also fail
> > > > the mount if folio_alloc fails?
> > > 
> > > Yes.  Like any other allocation that fails at mount time.
> > 
> > How hard is it to fallback to regular zero-page if you can't allocate
> > the zero-hugepage?
> 
> We'd need the bio allocation and bio_add_page loop.  Not the end
> of the world, but also a bit annoying.  If we do that we might as
> well just do it unconditionally.
> 
> > I think most sysadmins would rather mount with
> > reduced zeroing performance than get an ENOMEM.
> 
> If you don't have 2MB free for the zero huge folio, are you going to
> do useful things with your large block size XFS file system which
> only makes sense for giant storage sizes?

Oh.  Right, this is for bs>ps.  For that case it makes sense to fail the
mount.  I was only thinking about bs<=ps with large folios, where it
doesn't.

(Would we use the zero-hugepage for large folios on a 4k fsblock fs?)

--D




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