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Re: [PATCH 16/17] mem/memcg: cache rightmost node

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On Wed 26-07-17 14:09:27, Andrew Morton wrote:
> On Wed, 19 Jul 2017 09:50:36 +0200 Michal Hocko <mhocko@kernel.org> wrote:
> 
> > [CC Johannes and Vladimir - the whole series is
> > http://lkml.kernel.org/r/20170719014603.19029-1-dave@stgolabs.net]
> > 
> > On Tue 18-07-17 18:46:02, Davidlohr Bueso wrote:
> > > Such that we can optimize __mem_cgroup_largest_soft_limit_node().
> > > The only overhead is the extra footprint for the cached pointer,
> > > but this should not be an issue for mem_cgroup_tree_per_node.
> > 
> > The soft limit reclaim and the associated tree manipulation is not worth
> > touching/optimizing IMHO. We strongly discourage anybody configuring
> > soft limit because of the way how it is implemented and disruptive.
> 
> I'm inclined to merge this.  Unless we plan to actually remove the code
> "soon",

this is not going to happen. It is a user visible interface so we will
have to maintain it as long as cgroup v1 interface is available

> I think it's best to continue to improve it.  Improving
> performance may never matter to anyone, but there is benefit in keeping
> up to date with the current interfaces and best practices.
 
 Well, I am not opposing the change I just think it is not worth
 bothering. Soft limit reclaim tends to be so expensive (direct limit
 down to the soft limit) that a tiny otimization has hard times to help.

-- 
Michal Hocko
SUSE Labs

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[PATCH -next v4 00/17] rbtree: cache leftmost node internally Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 09/17] locking/rtmutex: replace top-waiter and pi_waiters leftmost caching Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 03/17] rbtree: add some additional comments for rebalancing cases Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 13/17] procfs: use faster rb_first_cached() Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 16/17] mem/memcg: cache rightmost node Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
    Re: [PATCH 16/17] mem/memcg: cache rightmost node Michal Hocko <mhocko@kernel.org> - 2017-07-19 10:00 +0200
      Re: [PATCH 16/17] mem/memcg: cache rightmost node Andrew Morton <akpm@linux-foundation.org> - 2017-07-26 23:10 +0200
        Re: [PATCH 16/17] mem/memcg: cache rightmost node Michal Hocko <mhocko@kernel.org> - 2017-07-27 09:10 +0200
  [PATCH 01/17] rbtree: cache leftmost node internally Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 17/17] block/cfq: cache rightmost rb_node Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
    Re: [PATCH 17/17] block/cfq: cache rightmost rb_node Jan Kara <jack@suse.cz> - 2017-07-19 10:00 +0200
  [PATCH 12/17] lib/interval-tree: correct comment wrt generic flavor Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
  [PATCH 10/17] block/cfq: replace cfq_rb_root leftmost caching Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 03:50 +0200
    Re: [PATCH 10/17] block/cfq: replace cfq_rb_root leftmost caching Jan Kara <jack@suse.cz> - 2017-07-19 09:50 +0200
  [PATCH 05/17] lib/rbtree_test.c: add (inorder) traversal test Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 04:00 +0200
  [PATCH 04/17] lib/rbtree_test.c: make input module parameters Davidlohr Bueso <dave@stgolabs.net> - 2017-07-19 04:00 +0200
  Re: [PATCH 11/17] lib/interval_tree: fast overlap detection Doug Ledford <dledford@redhat.com> - 2017-07-22 20:00 +0200

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