Re: [PATCH] ext4: Don't allow lg prealloc list to be grow large.

[Theodore Tso <tytso@mit.edu>]

On Wed, Jul 23, 2008 at 10:40:47PM +0530, Aneesh Kumar K.V wrote:
> Currently locality group prealloc list is freed only when there is a block allocation
> failure. This can result in large number of per cpu locality group prealloc space
> and also make the ext4_mb_use_preallocated expensive. Convert the locality group
> prealloc list to a hash list. The hash index is the order of number of blocks
> in the prealloc space with a max order of 9. When adding prealloc space to the
> list we make sure total entries for each order does not exceed 8. If it is more
> than 8 we discard few entries and make sure the we have only <= 5 entries.

So the second sentence made my english parser core dump.  :-)

I rewrote the patch comments as follows; is it still a fair summary?

    Currently, the locality group prealloc list is freed only when there
    is a block allocation failure. This can result in large number of
    entries in the preallocation list making ext4_mb_use_preallocated()
    expensive.
    
    To fix this, we convert the locality group prealloc list to a hash
    list. The hash index is the order of number of blocks in the prealloc
    space with a max order of 9. When adding prealloc space to the list we
    make sure total entries for each order does not exceed 8. If it is
    more than 8 we discard few entries and make sure the we have only <= 5
    entries.

							- Ted