On Mon, Jun 08, 2015 at 04:27:10PM -0400, Jeff Moyer wrote: > Jeff Moyer <jmoyer@xxxxxxxxxx> writes: > > > Tejun Heo <tj@xxxxxxxxxx> writes: > > > >> Even when allocations fail, cfq_find_alloc_queue() always returns a > >> valid cfq_queue by falling back to the oom cfq_queue. As such, there > >> isn't much point in taking @gfp_mask and trying "harder" if __GFP_WAIT > >> is set. GFP_ATOMIC allocations don't fail often and even when they do > >> the degraded behavior is acceptable and temporary. > >> > >> After all, the only reason get_request(), which ultimately determines > >> the gfp_mask, cares about __GFP_WAIT is to guarantee request > >> allocation, assuming IO forward progress, for callers which are > >> willing to wait. There's no reason for cfq_find_alloc_queue() to > >> behave differently on __GFP_WAIT when it already has a fallback > >> mechanism. > >> > >> Remove @gfp_mask from cfq_find_alloc_queue() and propagate the changes > >> to its callers. This simplifies the function quite a bit and will > >> help making async queues per-cfq_group. > > > > Sorry, I disagree with this patch. You've changed it so that all cfqq > > allocations are GFP_ATOMIC, and most, if not all of them simply don't > > need to be. > > It occurs to me that replacing GFP_ATOMIC with GFP_NOWAIT in your patch > would address my concerns, and patches 6-8 would apply almost as-is. > What do you think about that? Whatever we end up using, may be it is a good idea to use same policy for block group allocation too. Right now we use GFP_ATOMIC for blkcg allocation. So this will be equivalent of that when memory is low, we don't provide service differentiation. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
