Re: [PATCH v2] writeback: Do not sync data dirtied after sync start

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

Hi Jan,

On Thu, Sep 26, 2013 at 09:23:58PM +0200, Jan Kara wrote:
> When there are processes heavily creating small files while sync(2) is
> running, it can easily happen that quite some new files are created
> between WB_SYNC_NONE and WB_SYNC_ALL pass of sync(2). That can happen
> especially if there are several busy filesystems (remember that sync
> traverses filesystems sequentially and waits in WB_SYNC_ALL phase on one
> fs before starting it on another fs). Because WB_SYNC_ALL pass is slow
> (e.g. causes a transaction commit and cache flush for each inode in
> ext3), resulting sync(2) times are rather large.

This is a very good change. An old problem that may worth noting here
is that inode_dirtied_after() has a workaround for the inodes whose
->dirtied_when is never updated due to being constantly redirtied.
That workaround still leaves a small time window that sync() may skip
a should-be-synced inode. Since the problem existed before this patch
so I'm fine with this change.

Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>

Thanks!