On Thu, Dec 04, 2014 at 10:12:23AM -0500, Tejun Heo wrote: > From: NeilBrown <[email protected]> > > When there is serious memory pressure, all workers in a pool could be > blocked, and a new thread cannot be created because it requires memory > allocation. > > In this situation a WQ_MEM_RECLAIM workqueue will wake up the > rescuer thread to do some work. > > The rescuer will only handle requests that are already on ->worklist. > If max_requests is 1, that means it will handle a single request. > > The rescuer will be woken again in 100ms to handle another max_requests > requests. > > I've seen a machine (running a 3.0 based "enterprise" kernel) with > thousands of requests queued for xfslogd, which has a max_requests of > 1, and is needed for retiring all 'xfs' write requests. When one of > the worker pools gets into this state, it progresses extremely slowly > and possibly never recovers (only waited an hour or two). > > With this patch we leave a pool_workqueue on mayday list > until it is clearly no longer in need of assistance. This allows > all requests to be handled in a timely fashion. > > We keep each pool_workqueue on the mayday list until > need_to_create_worker() is false, and no work for this workqueue is > found in the pool. > > I have tested this in combination with a (hackish) patch which forces > all work items to be handled by the rescuer thread. In that context > it significantly improves performance. A similar patch for a 3.0 > kernel significantly improved performance on a heavy work load. > > Thanks to Jan Kara for some design ideas, and to Dongsu Park for > some comments and testing. > > tj: Inverted the lock order between wq_mayday_lock and pool->lock with > a preceding patch and simplified this patch. Added comment and > updated changelog accordingly. Dongsu spotted missing get_pwq() > in the simplified code. > > Cc: Dongsu Park <[email protected]> > Cc: Jan Kara <[email protected]> > Cc: Lai Jiangshan <[email protected]> > Signed-off-by: NeilBrown <[email protected]> > Signed-off-by: Tejun Heo <[email protected]>
Too late for for-3.18-fixes. Applied the two patches to wq/for-3.19. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
