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Re: [PATCH 0/5] memcg/kmem: switch to white list policy

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Hello, Vladmir.

On Mon, Nov 09, 2015 at 09:28:40PM +0300, Vladimir Davydov wrote:
> > I am _all_ for this semantic I am just not sure what to do with the
> > legacy kmem controller. Can we change its semantic? If we cannot do that
> 
> I think we can. If somebody reports a "bug" caused by this change, i.e.
> basically notices that something that used to be accounted is not any
> longer, it will be trivial to fix by adding __GFP_ACCOUNT where
> appropriate. If it is not, e.g. if accounting of objects of a particular
> type leads to intense false-sharing, we would end up disabling
> accounting for it anyway.

I agree too, if anything is meaningfully broken by the flip, it just
indicates that the whitelist needs to be expanded; however, I wonder
whether this would be done better at slab level rather than per
allocation site.

A class of objects which can consume noticeable amount of memory which
can be attributed to userland is likely to be on its own slab already
or separating it out to its own slab is likely to be a good idea.
Marking those slabs as kmemcg accounted seems better suited to the
semantics - it's always about classes of objects - and less
error-prone than marking individual allocation sites.

This also reduces the number of slabs to worry about and more
importantly makes it clear which slabs need to be replicated for
kmemcg accounting from the beginning and the slab part of
implementation can be far simpler / more static.

Thanks.

-- 
tejun
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[PATCH 0/5] memcg/kmem: switch to white list policy Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-07 21:10 +0100
  [PATCH 4/5] vmalloc: allow to account vmalloc to memcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-07 21:10 +0100
  [PATCH 3/5] memcg: only account kmem allocations marked as __GFP_ACCOUNT Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-07 21:10 +0100
  [PATCH 1/5] Revert "kernfs: do not account ino_ida allocations to memcg" Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-07 21:10 +0100
  Re: [PATCH 0/5] memcg/kmem: switch to white list policy Michal Hocko <mhocko@kernel.org> - 2015-11-09 15:10 +0100
    Re: [PATCH 0/5] memcg/kmem: switch to white list policy Johannes Weiner <hannes@cmpxchg.org> - 2015-11-09 17:50 +0100
    Re: [PATCH 0/5] memcg/kmem: switch to white list policy Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-09 19:30 +0100
      Re: [PATCH 0/5] memcg/kmem: switch to white list policy Tejun Heo <tj@kernel.org> - 2015-11-09 20:00 +0100
        Re: [PATCH 0/5] memcg/kmem: switch to white list policy Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-09 20:30 +0100
          Re: [PATCH 0/5] memcg/kmem: switch to white list policy Tejun Heo <tj@kernel.org> - 2015-11-09 20:40 +0100
            Re: [PATCH 0/5] memcg/kmem: switch to white list policy Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-09 21:20 +0100
              Re: [PATCH 0/5] memcg/kmem: switch to white list policy Tejun Heo <tj@kernel.org> - 2015-11-09 21:40 +0100
                Re: [PATCH 0/5] memcg/kmem: switch to white list policy Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-10 09:00 +0100
      Re: [PATCH 0/5] memcg/kmem: switch to white list policy Michal Hocko <mhocko@kernel.org> - 2015-11-11 09:20 +0100
  Re: [PATCH 5/5] Account certain kmem allocations to memcg Michal Hocko <mhocko@kernel.org> - 2015-11-09 15:50 +0100
    Re: [PATCH 5/5] Account certain kmem allocations to memcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-11-10 09:10 +0100
      Re: [PATCH 5/5] Account certain kmem allocations to memcg Michal Hocko <mhocko@kernel.org> - 2015-11-10 14:30 +0100

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