Writes are accounted for, but not reads. The supplied patch fixes this.

It seems that the accounting it normally done in the kernels page writeback and readahead
functionality. Therefore as Lustre implements its own readahead, it must also maintain its own
accounting on reads (but not writes).

Previously discussed in:

• http://lists.lustre.org/pipermail/lustre-devel-lustre.org/2011-April/001586.html
• https://bugzilla.lustre.org/show_bug.cgi?id=24536