Re: [PATCH V4] btrfs: implement delayed inode items operation

[Miao Xie <miaox@cn.fujitsu.com>]

On Mon, 21 Mar 2011 08:08:17 -0400, Chris Mason wrote:
>>> I also think that code is racing with the code that frees delayed nodes,
>>> but haven't yet triggered my debugging printks to prove either one.
>>
>> We free delayed nodes when we want to destroy the inode, at that time, just one task,
>> which is destroying inode, can access the delayed nodes, so I think ACCESS_ONCE() is
>> enough. What do you think about?
> 
> Great, I see what you mean.  The bigger problem right now is that we may do
> a lot of operations in destroy_inode(), which can block the slab
> shrinkers on our metadata operations.  That same stress.sh -n 50 run is
> running into OOM.
> 
> So we need to rework the part where the final free is done.  We could
> keep a ref on the inode until the delayed items are complete, or we
> could let the inode go and make a way to lookup the delayed node when
> the inode is read.

I find the slab shrinkers just reclaim inodes which are in the inode_unused
list, so if we free delayed nodes before moving the inode into the inode_unused
list, we can avoid blocking the slab shrinker. Thus maybe we can fix the above
problem by moving btrfs_remove_delayed_node() from btrfs_destroy_inode()
to btrfs_drop_inode(). How do you think about?

Thanks
Miao

> 
> I'll read more today.
> 
> -chris
>