On Thu, May 09, 2013 at 08:41:49AM -0700, Dave Hansen wrote: > On 05/08/2013 09:02 AM, Mel Gorman wrote: > > So preliminary testing indicates the results are mixed bag. As long as > > locks are not contended, it performs fine but parallel fault testing > > hits into spinlock contention on the magazine locks. A greater problem > > is that because CPUs share magazines it means that the struct pages are > > frequently dirtied cache lines. If CPU A frees a page to a magazine and > > CPU B immediately allocates it then the cache line for the page and the > > magazine bounces and this costs. It's on the TODO list to research if the > > available literature has anything useful to say that does not depend on > > per-cpu lists and the associated problems with them. > > If we don't want to bounce 'struct page' cache lines around, then we > _need_ to make sure that things that don't share caches don't use the > same magazine. I'm not sure there's any other way. But, that doesn't > mean we have to _statically_ assign cores/thread to particular magazines. > We could do something similar to sd_llc_id in kernel/sched/core.c to match CPUs to magazines where the data is likely to be at least in the last level cache. > Say we had a percpu hint which points us to the last magazine we used. > We always go to it first, and fall back to round-robin if our preferred > one is contended. That way, if we have a mixture tasks doing heavy and > light allocations, the heavy allocators will tend to "own" a magazine, > and the lighter ones would gravitate to sharing one. > We might not need the percpu hint if the sd_llc_id style hint was good enough. > It might be taking things too far, but we could even raise the number of > magazines only when we actually *see* contention on the existing set. > I had considered a similar idea. I think it would be relatively easy to grow the number of magazines or even allocate them on a per-process basis but it was less clear how it would be shrunk again. > > 24 files changed, 571 insertions(+), 788 deletions(-) > > oooooooooooooooooohhhhhhhhhhhhh. > > The only question is how much we'll have to bloat it as we try to > optimize things. :) > Indeed :/ > BTW, I really like the 'magazine' name. It's not frequently used in > this kind of context and it conjures up a nice mental image whether it > be of stacks of periodicals or firearm ammunition clips. I remember the term from the papers Christoph cited. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>