Messages in this thread | | | Date | Thu, 27 Mar 2008 11:38:31 +0300 | From | Pavel Emelyanov <> | Subject | Re: [RFC][2/3] Account and control virtual address space allocations (v2) |
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[snip]
>>>>> + css_put(&mem->css); >>>> Why don't you check whether the counter is charged? This is >>>> bad for two reasons: >>>> 1. you allow for some growth above the limit (e.g. in expand_stack) >>> I was doing that earlier and then decided to keep the virtual address space code >>> in sync with the RLIMIT_AS checking code in the kernel. If you see the flow, it >>> closely resembles what we do with mm->total_vm and may_expand_vm(). >>> expand_stack() in turn calls acct_stack_growth() which calls may_expand_vm() >> But this is racy! Look - you do expand_stack on two CPUs and the limit is >> almost reached - so that there's room for a single expansion. In this case >> may_expand_vm will return true for both, since it only checks the limit, >> while the subsequent charge will fail on one of them, since it actually >> tries to raise the usage... >> > > Hmm... yes, possibly. Thanks for pointing this out. For a single mm_struct, the > check is done under mmap_sem(), so it's OK for processes. I suspect, I'll have
Sure, but this controller should work with arbitrary group of processes ;)
> to go back to what I had earlier. I don't want to add a mutex to mem_cgroup, > that will hurt parallelism badly.
My opinion is that we should always perform a pure charge without any pre-checks, etc.
Thanks, Pavel
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