[Lustre-devel] client i/o and PG_writeback

[Johann Lombardi]

On Thu, Aug 11, 2011 at 02:40:23PM -0700, Jinshan Xiong wrote:
> This really means PG_writeback is useless. The most important benefit of
> PG_writeback is to allow to write a being flushed page.

The benefit of PG_writeback is that one can check whether or not a page is under writeback and decide to wait for writeback to complete (via wait_on_page_writeback()) or to skip this page. A good example is the linux kernel writeback code which waits for writeback to complete for WB_SYNC_ALL (data integrity flush), but not for WB_SYNC_NONE (just regular memory cleaning writeback).

Cheers,
Johann
-- 
Johann Lombardi
Whamcloud, Inc.
www.whamcloud.com