linux-kernel - Re: [PATCH v10 10/10] xfs: enable block size larger than page size support

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Message-ID: <20240716174016.GZ1998502@frogsfrogsfrogs>
Date: Tue, 16 Jul 2024 10:40:16 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
	david@...morbit.com, chandan.babu@...cle.com, brauner@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	yang@...amperecomputing.com, linux-mm@...ck.org,
	john.g.garry@...cle.com, linux-fsdevel@...r.kernel.org,
	hare@...e.de, p.raghav@...sung.com, mcgrof@...nel.org,
	gost.dev@...sung.com, cl@...amperecomputing.com,
	linux-xfs@...r.kernel.org, ryan.roberts@....com, hch@....de,
	Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v10 10/10] xfs: enable block size larger than page size
 support

On Tue, Jul 16, 2024 at 04:29:05PM +0100, Matthew Wilcox wrote:
> On Mon, Jul 15, 2024 at 11:44:57AM +0200, Pankaj Raghav (Samsung) wrote:
> > +++ b/fs/xfs/xfs_super.c
> > @@ -1638,16 +1638,30 @@ xfs_fs_fill_super(
> >  		goto out_free_sb;
> >  	}
> >  
> > -	/*
> > -	 * Until this is fixed only page-sized or smaller data blocks work.
> > -	 */
> >  	if (mp->m_sb.sb_blocksize > PAGE_SIZE) {
> > -		xfs_warn(mp,
> > -		"File system with blocksize %d bytes. "
> > -		"Only pagesize (%ld) or less will currently work.",
> > +		size_t max_folio_size = mapping_max_folio_size_supported();
> > +
> > +		if (!xfs_has_crc(mp)) {
> > +			xfs_warn(mp,
> > +"V4 Filesystem with blocksize %d bytes. Only pagesize (%ld) or less is supported.",
> >  				mp->m_sb.sb_blocksize, PAGE_SIZE);
> > -		error = -ENOSYS;
> > -		goto out_free_sb;
> > +			error = -ENOSYS;
> > +			goto out_free_sb;
> > +		}
> > +
> > +		if (mp->m_sb.sb_blocksize > max_folio_size) {
> > +			xfs_warn(mp,
> > +"block size (%u bytes) not supported; maximum folio size supported in "\
> > +"the page cache is (%ld bytes). Check MAX_PAGECACHE_ORDER (%d)",
> > +			mp->m_sb.sb_blocksize, max_folio_size,
> > +			MAX_PAGECACHE_ORDER);
> 
> Again, too much message.  Way too much.  We shouldn't even allow block
> devices to be created if their block size is larger than the max supported
> by the page cache.

Filesystem blocksize != block device blocksize.  xfs still needs this
check because one can xfs_copy a 64k-fsblock xfs to a hdd with 512b
sectors and try to mount that on x86.

Assuming there /is/ some fs that allows 1G blocksize, you'd then really
want a mount check that would prevent you from mounting that.

--D