linux-kernel - Re: [PATCH v12 00/10] enable bs

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Message-ID: <df26beed-97c7-44e4-b380-2260b8331ea9@suse.de>
Date: Mon, 19 Aug 2024 09:24:11 +0200
From: Hannes Reinecke <hare@...e.de>
To: David Howells <dhowells@...hat.com>,
 "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: brauner@...nel.org, akpm@...ux-foundation.org, chandan.babu@...cle.com,
 linux-fsdevel@...r.kernel.org, djwong@...nel.org, gost.dev@...sung.com,
 linux-xfs@...r.kernel.org, hch@....de, david@...morbit.com,
 Zi Yan <ziy@...dia.com>, yang@...amperecomputing.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, willy@...radead.org,
 john.g.garry@...cle.com, cl@...amperecomputing.com, p.raghav@...sung.com,
 mcgrof@...nel.org, ryan.roberts@....com
Subject: Re: [PATCH v12 00/10] enable bs > ps in XFS

On 8/18/24 22:16, David Howells wrote:
> Pankaj Raghav (Samsung) <kernel@...kajraghav.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?

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.

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.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich