Re: [PATCH v12 00/10] enable bs > ps in XFS

Pankaj Raghav (Samsung)
2024-08-19T07:37:58Z

On Mon, Aug 19, 2024 at 09:24:11AM +0200, Hannes Reinecke wrote:
> On 8/18/24 22:16, David Howells wrote:
> > Pankaj Raghav (Samsung) <kernel@pankajraghav.com> wrote:
> >
> > > I am no expert in network filesystems but are you sure there are no
> > > PAGE_SIZE assumption when manipulating folios from the page cache in
> > > AFS?
> >
> > Note that I've removed the knowledge of the pagecache from 9p, afs and cifs to
> > netfslib and intend to do the same to ceph. The client filesystems just
> > provide read and write ops to netfslib and netfslib uses those to do ordinary
> > buffered I/O, unbuffered I/O (selectable by mount option on some filesystems)
> > and DIO.
> >
> > That said, I'm not sure that I haven't made some PAGE_SIZE assumptions. I
> > don't *think* I have since netfslib is fully multipage folio capable, but I
> > can't guarantee it.
> >
> I guess you did:
>
> static int afs_fill_super(struct super_block *sb, struct afs_fs_context
> *ctx)
> {
> struct afs_super_info *as = AFS_FS_S(sb);
> struct inode *inode = NULL;
> int ret;
>
> _enter("");
>
> /* fill in the superblock */
> sb->s_blocksize = PAGE_SIZE;
> sb->s_blocksize_bits = PAGE_SHIFT;
> sb->s_maxbytes = MAX_LFS_FILESIZE;
> sb->s_magic = AFS_FS_MAGIC;
> sb->s_op = &afs_super_ops;
>
> IE you essentially nail AFS to use PAGE_SIZE.
> Not sure how you would tell AFS to use a different block size;
> maybe a mount option?

I saw this as well, but I didn't see this variable being used anywhere.
Probably this has no meaning in a network-based FSs?

> And there are several other places which will need to be modified;
> eg afs_mntpt_set_params() is trying to read from a page which
> won't fly with large blocks (converted to read_full_folio()?),
> and, of course, the infamous AFS_DIR_BLOCKS_PER_PAGE which will
> overflow for large blocks.

But the min folio order is set only for AFS_FTYPE_FILE and not
for AFS_FTYPE_DIR.

>
> So some work is required, but everything looks doable.
> Maybe I can find some time until LPC.
>
> > Mostly this was just a note to you that there might be an issue with your code
> > - but I haven't investigated it yet and it could well be in my code.
> >
> Hmm. I'd rather fix the obvious places in afs first; just do a quick
> grep for 'PAGE_', that'll give you a good impression of places to look at.
>
Agree.

> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke Kernel Storage Architect
> hare@suse.de +49 911 74053 688
> SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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>