Re: [RFC] vfs/inode: For none-block-based filesystems default to sb->s_bdi

[Boaz Harrosh <bharrosh@panasas.com>]

On 10/05/2010 11:09 AM, Jan Kara wrote:
> On Tue 05-10-10 09:53:41, Boaz Harrosh wrote:
>> On 10/05/2010 04:32 AM, Jan Kara wrote:
>>>   Hi Boaz,
>>>
>>> On Mon 04-10-10 18:02:13, Boaz Harrosh wrote:
>>>> Sorry I've just seen Jan's patch:
>>>> From: Jan Kara <jack@suse.cz>
>>>> Date: Mon, 27 Sep 2010 23:56:48 +0200
>>>> Subject: [PATCH] bdi: Initialize inode->i_mapping.backing_dev_info to sb->s_bdi
>>> ...
>>>> That works for me as well. Was it decided how to solve this? Other wise
>>>> I'll need to patch exofs, ASAP for this -rc
>>>   In the end, we'll use Christoph's patch
>>> (http://lkml.org/lkml/2010/9/29/76) changing inode_to_bdi() to be
>>> more conservative and also the warning will be gone. So you don't have to
>>> patch anything...
>>>
>> I would still like to fix it. Currently each inode->mapping.backing_dev_info in my
>> none-block-filesystem is set to &default_backing_dev_info. This sounds scary!
>> what about the future patches that will schedule a wakup on set_inode_dirty ?
>> Will they not need my proper sb->s_bdi on each ->mapping?
>   Yes, but Christoph is working on separating the bdi handling from
> handling of writeback (pointed from superblock) and that should solve this
> problem as well.
> 

If you are right and inode->i_mapping.backing_dev_info will only be used for bdev
inodes, then I prefer if it would be NULL by default and not pointing to
&default_backing_dev_info. Will that be fixed as well?

diff --git a/fs/inode.c b/fs/inode.c
index 8646433..0ec4c47 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -168,7 +168,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	mapping->flags = 0;
 	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
 	mapping->assoc_mapping = NULL;
-	mapping->backing_dev_info = &default_backing_dev_info;
+	mapping->backing_dev_info = NULL;
 	mapping->writeback_index = 0;
 
 	/*

Current code in inode_init_always() looks really ugly with that if(sb->s_bdev) ...
surely you want to fix that too, No?

> 								Honza

Boaz