Hi Tejun, On Fri, Aug 28, 2015 at 11:25:29AM -0400, Tejun Heo wrote: > Currently, try_charge() tries to reclaim memory directly when the high > limit is breached; however, this has a couple issues. > > * try_charge() can be invoked from any in-kernel allocation site and > reclaim path may use considerable amount of stack. This can lead to > stack overflows which are extremely difficult to reproduce. IMO this paragraph does not justify this patch at all, because one will still invoke direct reclaim from try_charge() on hitting the hard limit. > > * If the allocation doesn't have __GFP_WAIT, direct reclaim is > skipped. If a process performs only speculative allocations, it can > blow way past the high limit. This is actually easily reproducible > by simply doing "find /". VFS tries speculative !__GFP_WAIT > allocations first, so as long as there's memory which can be > consumed without blocking, it can keep allocating memory regardless > of the high limit. I think there shouldn't normally occur a lot of !__GFP_WAIT allocations in a row - they should still alternate with normal __GFP_WAIT allocations. Yes, that means we can breach memory.high threshold for a short period of time, but it isn't a hard limit, so it looks perfectly fine to me. I tried to run `find /` over ext4 in a cgroup with memory.high set to 32M and kmem accounting enabled. With such a setup memory.current never got higher than 33152K, which is only 384K greater than the memory.high. Which FS did you use? Thanks, Vladimir -- 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
