Re: [PATCH 2/7] Assign bdi in super_block
From: Jens Axboe
Date: Mon Sep 14 2009 - 14:37:02 EST
On Mon, Sep 14 2009, Trond Myklebust wrote:
>
On Mon, 2009年09月14日 at 15:02 +0200, Jan Kara wrote:
>
> On Mon 14-09-09 11:36:29, Jens Axboe wrote:
>
> > We do this automatically in get_sb_bdev() from the set_bdev_super()
>
> > callback. Filesystems that have their own private backing_dev_info
>
> > must assign that in ->fill_super().
>
> >
>
> > Note that ->s_bdi assignment is required for proper writeback!
>
> >
>
> > Acked-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
>
> > Signed-off-by: Jens Axboe <jens.axboe@xxxxxxxxxx>
>
> Hmm, looking at this again, I'm not sure this will work for NFS. It seems
>
> to set mapping->backing_dev_info to its private backing dev info for
>
> regular files while it leaves it intact for other inodes (e.g.
>
> directories). I'm not sure why it does so but it seems its inodes end up on
>
> two different BDI lists and thus they wouldn't be synced properly. Trond,
>
> do I read the code properly?
>
> Also we definitely need to set *some* bdi in nfs_get_sb as otherwise sync
>
> won't work for it.
>
>
There hasn't really been a need for a bdi in NFS other than for the
>
regular file read and writeback code. The main reason for making it
>
private was to ensure that we could set a per-superblock readahead limit
>
that was a decent multiple of the server's preferred read block size.
>
>
Is there any reason why we couldn't set sb->s_bdi to point to that
>
private bdi?
No, that should work fine. NFS already works fine with the bdi flusher
threads, so you should just point it at that bdi.
If you could take a look at the parent patch and give some input (or an
addition for NFS, even better), then I would much appreciate it.
--
Jens Axboe
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