Re: [PATCH 1/5] writeback: introduce wbc.for_sync to cover the two sync stages

[Wu Fengguang <fengguang.wu@intel.com>]

On Thu, Jul 29, 2010 at 11:04:13PM +0800, Jan Kara wrote:
> On Thu 29-07-10 19:51:43, Wu Fengguang wrote:
> > The sync() is performed in two stages: the WB_SYNC_NONE sync and
> > the WB_SYNC_ALL sync. It is necessary to tag both stages with
> > wbc.for_sync, so as to prevent either of them being livelocked.
> > 
> > The basic livelock scheme will be based on the sync_after timestamp.
> > Inodes dirtied after that won't be queued for IO. The timestamp could be
> > recorded as early as the sync() time, this patch lazily sets it in
> > writeback_inodes_sb()/sync_inodes_sb(). This will stop livelock, but
> > may do more work than necessary.
> > 
> > Note that writeback_inodes_sb() is called by not only sync(), they
> > are treated the same because the other callers need the same livelock
> > prevention.

>   OK, but the patch does nothing, doesn't it? I'd prefer if the fields
> you introduce were actually used in this patch.

OK, I'll merge it with the third patch.

Thanks,
Fengguang