Messages in this thread | | | Date | Wed, 09 Jan 2013 16:24:34 +0900 | From | Kamezawa Hiroyuki <> | Subject | Re: [PATCH V3 4/8] memcg: add per cgroup dirty pages accounting |
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(2013/01/09 14:15), Hugh Dickins wrote: > On Mon, 7 Jan 2013, Kamezawa Hiroyuki wrote: >> (2013/01/07 5:02), Hugh Dickins wrote: >>> >>> Forgive me, I must confess I'm no more than skimming this thread, >>> and don't like dumping unsigned-off patches on people; but thought >>> that on balance it might be more helpful than not if I offer you a >>> patch I worked on around 3.6-rc2 (but have updated to 3.8-rc2 below). >>> >>> I too was getting depressed by the constraints imposed by >>> mem_cgroup_{begin,end}_update_page_stat (good job though Kamezawa-san >>> did to minimize them), and wanted to replace by something freer, more >>> RCU-like. In the end it seemed more effort than it was worth to go >>> as far as I wanted, but I do think that this is some improvement over >>> what we currently have, and should deal with your recursion issue. >>> >> In what case does this improve performance ? > > Perhaps none. I was aiming to not degrade performance at the stats > update end, and make it more flexible, so new stats can be updated which > would be problematic today (for lock ordering and recursion reasons). > > I've not done any performance measurement on it, and don't have enough > cpus for an interesting report; but if someone thinks it might solve a > problem for them, and has plenty of cpus to test with, please go ahead, > we'd be glad to hear the results. > >> Hi, this patch seems interesting but...doesn't this make move_account() very >> slow if the number of cpus increases because of scanning all cpus per a page >> ? >> And this looks like reader-can-block-writer percpu rwlock..it's too heavy to >> writers if there are many readers. > > I was happy to make the relatively rare move_account end considerably > heavier. I'll be disappointed if it turns out to be prohibitively > heavy at that end - if we're going to make move_account impossible, > there are much easier ways to achieve that! - but it is a possibility. >
move_account at task-move has been required feature for NEC and Nishimura-san did good job. I'd like to keep that available as much as possible.
> Something you might have missed when considering many readers (stats > updaters): the move_account end does not wait for a moment when there > are no readers, that would indeed be a losing strategy; it just waits > for each cpu that's updating page stats to leave that section, so every > cpu is sure to notice and hold off if it then tries to update the page > which is to be moved. (I may not be explaining that very well!) >
Hmm, yeah, maybe I miss somehing.
BTW, if nesting, mem_cgroup_end_update_page_stat() seems to make counter minus.
Thanks, -Kame
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