Re: [PATCH 01/15] writeback: introduce .tagged_writepages for the WB_SYNC_NONE sync stage

Andrew Morton
2011-06-07T23:03:21Z

On Wed, 08 Jun 2011 05:32:37 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

> sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
> WB_SYNC_ALL sync. Identify the first stage with .tagged_writepages and
> do livelock prevention for it, too.
>
> Note that writeback_inodes_sb() is called by not only sync(), they are
> treated the same because the other callers also need livelock prevention.
>
> Impact: It changes the order in which pages/inodes are synced to disk.
> Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
> until finished with the current inode.

What problem is this patch actually fixing? It sounds like there's
some livelock scenario in the WB_SYNC_NONE phase. otoh the final
paragraph implies that the WB_SYNC_NONE phase is failing to write some
pages under some situations.

Suggest that the changelog be fleshed out to cover all of this.