Messages in this thread | | | Date | Thu, 27 Sep 2012 15:43:07 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH v3 04/13] kmem accounting basic infrastructure |
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On Thu, Sep 27, 2012 at 07:33:00AM -0700, Tejun Heo wrote: > Hello, Michal. > > On Thu, Sep 27, 2012 at 02:08:06PM +0200, Michal Hocko wrote: > > Yes, because we have many users (basically almost all) who care only > > about the user memory because that's what occupies the vast majority of > > the memory. They usually want to isolate workload which would disrupt > > the global memory otherwise (e.g. backup process vs. database). You > > really do not want to pay an additional overhead for kmem accounting > > here. > > I'm not too convinced. First of all, the overhead added by kmemcg > isn't big.
Really?
If kmemcg was globally accounted then every __GFP_KMEMCG allocation in the page allocator potentially ends up down in __memcg_kmem_newpage_charge which
1. takes RCU read lock 2. looks up cgroup from task 3. takes a reference count 4. memcg_charge_kmem -> __mem_cgroup_try_charge 5. release reference count
That's a *LOT* of work to incur for cgroups that do not care about kernel accounting. This is why I thought it was reasonable that the kmem accounting not be global.
-- Mel Gorman SUSE Labs
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