On Fri, Dec 18, 2015 at 12:51:07PM +1100, NeilBrown wrote: > > if the reclaim thread doesn't have anything to reclaim, > > r5l_run_no_space_stripes isn't called. we might miss the retry. > > so something like this: that looks fine to me. I'll give a spin on my QA setup. > > I'm a little worrying about the GFP_ATOMIC allocation. In the first try, > > GFP_NOWAIT is better. And on the other hand, why sleep is bad here? We > > could use GFP_NOIO | __GFP_NORETRY, there is no deadlock risk. > > > > In the retry, GFP_NOIO looks better. No deadlock too, since it's not > > called from raid5d (maybe we shouldn't call from reclaim thread if using > > GFP_NOIO, a workqueue is better). Otherwise we could keep retring but do > > nothing. > > I did wonder a little bit about that. > GFP_ATOMIC is (__GFP_HIGH) > GFP_NOIO | __GFP_NORETRY is (__GFP_WAIT | __GFP_NORETRY) > > It isn't clear that we need 'HIGH', and WAIT with NORETRY should be OK. > It allows __alloc_pages_direct_reclaim, but only once and never waits > for other IO. In general we go for HIGH on non-sleeping allocation to avoid having the stalled. This is especially important in the I/O path. WAIT means we will reclaim and wait for it, which looks a little dangerous to me. In general I'd prefer not to use obscure gfp flag combination unless there is a real need, and it's clearly documented. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
