Messages in this thread | | | Date | Wed, 3 Feb 2010 17:55:26 +0530 | From | Balbir Singh <> | Subject | Re: Improving OOM killer |
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* Lubos Lunak <l.lunak@suse.cz> [2010-02-03 13:10:27]:
> On Wednesday 03 of February 2010, Balbir Singh wrote: > > * Lubos Lunak <l.lunak@suse.cz> [2010-02-01 23:02:37]: > > > In other words, use VmRSS for measuring memory usage instead of VmSize, > > > and remove child accumulating. > > > > I am not sure of the impact of changing to RSS, although I've > > personally believed that RSS based accounting is where we should go, > > but we need to consider the following > > > > 1. Total VM provides data about potentially swapped pages, > > Yes, I've already updated my proposal in another mail to switch from VmSize > to VmRSS+InSwap. I don't know how to find out the second item in code, but at > this point of discussion that's just details. >
I am yet to catch up with the rest of the thread. Thanks for heads up.
> > overcommit, > > I don't understand how this matters. Overcommit is memory for which address > space has been allocated but not actual memory, right? Then that's exactly > what I'm claiming is wrong and am trying to reverse. Currently OOM killer > takes this into account because it uses VmSize, but IMO it shouldn't - if a > process does malloc(400M) but then it uses only a tiny fraction of that, in > the case of memory shortage killing that process does not solve anything in > practice.
We have a way of tracking commmitted address space, which is more sensible than just allocating memory and is used for tracking overcommit. I was suggesting that, that might be a better approach.
> > > etc. > > 2. RSS alone is not sufficient, RSS does not account for shared pages, > > so we ideally need something like PSS. > > Just to make sure I understand what you mean with "RSS does not account for > shared pages" - you say that if a page is shared by 4 processes, then when > calculating badness for them, only 1/4 of the page should be counted for > each? Yes, I suppose so, that makes sense.
Yes, that is what I am speaking of
> That's more like fine-tunning at > this point though, as long as there's no agreement that moving away from > VmSize is an improvement. >
There is no easy way to calculate the Pss today without walking the page tables, but some simplification there will make it a better and a more accurate metric.
> > I suspect the correct answer would depend on our answers to 1 and 2 > > and a lot of testing with any changes made. > > Testing - are there actually any tests for it, or do people just test random > scenarios when they do changes? Also, I'm curious, what areas is the OOM > killer actually generally known to work well in? I somehow get the feeling > from the discussion here that people just tweak oom_adj until it works for > them. >
I've mostly found OOM killer to work well for me, but looking at the design and our discussions I know there need to be certain improvements.
-- Balbir
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