[Ocfs2-devel] [patch 0/2] Add inode steal in ocfs2-1.2

[Tao Ma <tao.ma@oracle.com>]

One more thing, it has been tested with my script which has been sent to 
ocfs2-tools-devel for review. Please see
http://oss.oracle.com/pipermail/ocfs2-tools-devel/2008-March/000621.html

Regards,
Tao

tao.ma at oracle.com wrote:
> Hi all,
> This patch series add inode steal mechanism for inode allocation and
> it is backported from 2.6.26.
> 
> In OCFS2, we allocate the inodes from slot specific inode_alloc to avoid
> inode creation congestion. The local alloc file grows in a large contiguous
> chunk. As for a 4K bs, it grows 4M every time. So 1024 inodes will be
> allocated at a time.
> 
> Over time, if the fs gets fragmented enough(e.g, the user has created
> many small files and also delete some of them), we can end up in a situation,
> whereby we cannot extend the inode_alloc as we don't have a large chunk
> free in the global_bitmap even if df shows few gigs free. More annoying
> is that this situation will invariably mean that while one cannot create
> inodes on one node but can from another node. Still more annoying is that an
> unused slot may have space for plenty of inodes but is unusable as the user may
> not be mounting as many nodes anymore.
> 
> This patch series implement a solution which is to steal inodes from
> another slot. Now the whole inode allocation process looks like this:
> 1. Allocate from its own inode_alloc:000X
>    1) If we can reserve, OK.
>    2) If fails, try to allocate a large chunk and reserve once again.
> 2. If 1 fails, try to allocate from the ocfs2_super->inode_steal_slot.
>    This time, Just try to reserve, we don't go for global_bitmap if
>    this inode also can't allocate the inode.
> 3. If 2 fails, try the node next until we reach that steal slot again.
> 
> ocfs2_super->inode_steal_slot is initalized as the node next to our own
> slot. And once the inode stealing successes, we will refresh it with
> the slot we steal inode from. It will also be reinitalized when the
> local truncate log or local alloc recovery is flushed in which case the global
> bitmap may be refreshed.
>