Messages in this thread | | | Date | Sat, 29 Aug 2009 00:21:50 +0900 (JST) | Subject | Re: [RFC][PATCH 2/5] memcg: uncharge in batched manner | From | "KAMEZAWA Hiroyuki" <> |
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Balbir Singh さんは書きました: > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-08-28 > 13:24:38]: > >> >> In massive parallel enviroment, res_counter can be a performance >> bottleneck. >> This patch is a trial for reducing lock contention. >> One strong techinque to reduce lock contention is reducing calls by >> batching some amount of calls int one. >> >> Considering charge/uncharge chatacteristic, >> - charge is done one by one via demand-paging. >> - uncharge is done by >> - in chunk at munmap, truncate, exit, execve... >> - one by one via vmscan/paging. >> >> It seems we hace a chance to batched-uncharge. >> This patch is a base patch for batched uncharge. For avoiding >> scattering memcg's structure, this patch adds memcg batch uncharge >> information to the task. please see start/end usage in next patch. >> > > Overall it is a very good idea, can't we do the uncharge at the poin > tof unmap_vmas, exit_mmap, etc so that we don't have to keep > additional data structures around. > We can't. We uncharge when page->mapcount goes down to 0. This is unknown until page_remove_rmap() decrement page->mapcount by "atomic" ops.
My first version allocated memcg_batch_info on stack ...and.. I had to pass an extra argument to page_remove_rmap() etc.... That was very ugly ;( Now, I adds per-task memcg_batch_info to task struct. Because it will be always used at exit() and make exit() path much faster, it's not very costly.
Thanks, -Kame
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