On Thu, 11 Mar 2010 10:03:07 -0500 Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > On Thu, Mar 11, 2010 at 06:25:00PM +0900, KAMEZAWA Hiroyuki wrote: > > On Thu, 11 Mar 2010 10:14:25 +0100 > > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > On Thu, 2010-03-11 at 10:17 +0900, KAMEZAWA Hiroyuki wrote: > > > > On Thu, 11 Mar 2010 09:39:13 +0900 > > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > > > > 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. > > > > > > FWIW bit spinlocks suck massive. > > > > > > > > > > > > > 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. > > > > > > > > > But overall patch set seems good (to me.) And dirty_ratio and dirty_background_ratio > > > > will give us much benefit (of performance) than we lose by small overheads. > > > > > > Well, the !cgroup or root case should really have no performance impact. > > > > > > > IIUC, this series affects trgger for background-write-out. > > > > > > Not sure though, while this does the accounting the actual writeout is > > > still !cgroup aware and can definately impact performance negatively by > > > shrinking too much. > > > > > > > Ah, okay, your point is !cgroup (ROOT cgroup case.) > > I don't think accounting these file cache status against root cgroup is necessary. > > > > I think what peter meant was that with memory cgroups created we will do > writeouts much more aggressively. > > In balance_dirty_pages() > > if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh) > break; > > Now with Andrea's patches, we are calculating bdi_thres per memory cgroup > (almost) hmm. > > bdi_thres ~= per_memory_cgroup_dirty * bdi_fraction > > But bdi_nr_reclaimable and bdi_nr_writeback stats are still global. > Why bdi_thresh of ROOT cgroup doesn't depend on global number ? > So for the same number of dirty pages system wide on this bdi, we will be > triggering writeouts much more aggressively if somebody has created few > memory cgroups and tasks are running in those cgroups. > > I guess it might cause performance regressions in case of small file > writeouts because previously one could have written the file to cache and > be done with it but with this patch set, there are higher changes that > you will be throttled to write the pages back to disk. > > I guess we need two pieces to resolve this. > - BDI stats per cgroup. > - Writeback of inodes from same cgroup. > > I think BDI stats per cgroup will increase the complextiy. > Thank you for clarification. IIUC, dirty_limit implemanation shoul assume there is I/O resource controller, maybe usual users will use I/O resource controller and memcg at the same time. Then, my question is what happens when used with I/O resource controller ? > I am still setting up the system to test whether we see any speedup in > writeout of large files with-in a memory cgroup with small memory limits. > I am assuming that we are expecting a speedup because we will start > writeouts early and background writeouts probably are faster than direct > reclaim? > Yes. I think so. 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>