Re: forcing write-back from FS - again

Artem Bityutskiy
2007-10-22T09:51:20Z

Andrew Morton wrote:
>> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
>> @@ -28,6 +28,7 @@ static inline int task_is_pdflush(struct task_struct *task)
>> */
>> enum writeback_sync_modes {
>> WB_SYNC_NONE, /* Don't wait on anything */
>> + WB_SYNC_NONE_PG,/* Don't wait on anything, don't touch locked pages */
>> WB_SYNC_ALL, /* Wait on every mapping */
>> WB_SYNC_HOLD, /* Hold the inode on sb_dirty for sys_sync() */
>> };
>
> It would be simpler/safer/saner to add a new bitflag to writeback_control
> and use that directly. The WB_SYNC_foo flags are a holdover from an
> earlier time and really should be made to go away, in favour of directly
> setting up an appropriate writeback_control.

You mean something like (wbc->flags & WB_SYNC_NONE) etc? But below you used
wbc->skip_locked_pages, I'm confused.

> The code you have there looks racy: if someone else locks the page in that
> little window after the PageLocked() test we'll still block in lock_page().
> That's unlikely to happen in your application (apart from a remaining
> ab/ba scenario) but we should make it robust:
>
> if (wbc->skip_locked_pages) {
> if (TestSetPageLocked(page))
> continue;
> } else {
> lock_page(page);
> }

Yeah, thanks for the pointer! Thank you for your help on the issue!