On Wed, 10 Mar 2010 00:00:31 +0100 Andrea Righi <arighi@xxxxxxxxxxx> wrote: > Control the maximum amount of dirty pages a cgroup can have at any given time. > > Per cgroup dirty limit is like fixing the max amount of dirty (hard to reclaim) > page cache used by any cgroup. So, in case of multiple cgroup writers, they > will not be able to consume more than their designated share of dirty pages and > will be forced to perform write-out if they cross that limit. > > The overall design is the following: > > - account dirty pages per cgroup > - limit the number of dirty pages via memory.dirty_ratio / memory.dirty_bytes > and memory.dirty_background_ratio / memory.dirty_background_bytes in > cgroupfs > - start to write-out (background or actively) when the cgroup limits are > exceeded > > This feature is supposed to be strictly connected to any underlying IO > controller implementation, so we can stop increasing dirty pages in VM layer > and enforce a write-out before any cgroup will consume the global amount of > dirty pages defined by the /proc/sys/vm/dirty_ratio|dirty_bytes and > /proc/sys/vm/dirty_background_ratio|dirty_background_bytes limits. > > Changelog (v5 -> v6) > ~~~~~~~~~~~~~~~~~~~~~~ > * always disable/enable IRQs at lock/unlock_page_cgroup(): this allows to drop > the previous complicated locking scheme in favor of a simpler locking, even > if this obviously adds some overhead (see results below) > * drop FUSE and NILFS2 dirty pages accounting for now (this depends on > charging bounce pages per cgroup) > > Results > ~~~~~~~ > I ran some tests using a kernel build (2.6.33 x86_64_defconfig) on a > Intel Core 2 @ 1.2GHz as testcase using different kernels: > - mmotm "vanilla" > - mmotm with cgroup-dirty-memory using the previous "complex" locking scheme > (my previous patchset + the fixes reported by Kame-san and Daisuke-san) > - mmotm with cgroup-dirty-memory using the simple locking scheme > (lock_page_cgroup() with IRQs disabled) > > Following the results: > <before> > - mmotm "vanilla", root cgroup: 11m51.983s > - mmotm "vanilla", child cgroup: 11m56.596s > > <after> > - mmotm, "complex" locking scheme, root cgroup: 11m53.037s > - mmotm, "complex" locking scheme, child cgroup: 11m57.896s > > - mmotm, lock_page_cgroup+irq_disabled, root cgroup: 12m5.499s > - mmotm, lock_page_cgroup+irq_disabled, child cgroup: 12m9.920s > > With the "complex" locking solution, the overhead introduced by the > cgroup dirty memory accounting is minimal (0.14%), compared with the overhead > introduced by the lock_page_cgroup+irq_disabled solution (1.90%). > Hmm....isn't this bigger than expected ? > The performance overhead is not so huge in both solutions, but the impact on > performance is even more reduced using a complicated solution... > > Maybe we can go ahead with the simplest implementation for now and start to > think to an alternative implementation of the page_cgroup locking and > charge/uncharge of pages. > maybe. But in this 2 years, one of our biggest concerns was the performance. So, we do something complex in memcg. But complex-locking is , yes, complex. Hmm..I don't want to bet we can fix locking scheme without something complex. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>