[PATCH] Handle high-order allocation failures in ubifs_jnl_write_data

[Artem Bityutskiy]

On Fri, 2011-03-04 at 17:55 -0500, Matthew L. Creech wrote:
> Running kernel 2.6.37, my PPC-based device occasionally gets an
> order-2 allocation failure in UBIFS, which causes the root FS to
> become unwritable:

Matthew, I've massaged your patch a bit. The changes I've made are as
follows.

1. Some more commentaries and some re-naming.
2. Kill the union.
4. Tweak patch commit message.
5. Allocate write reserve buffer dynamically
6. Allocate write reserve buffer only when mounting in R/W mode to
   save some RAM when we are in R/O mode.
7. Free the buffer when we are remounting to R/O mode and allocate it
   again when re-mounting to R/W mode.

The patch is below. Please, let me know if you are OK with this patch.
I've also pushed it to ubifs-2.6.git / master.