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    SubjectRe: [patch 01/11] mm: memcg: consolidate hierarchy iteration primitives
    On Tue 20-09-11 10:45:53, Johannes Weiner wrote:
    > On Mon, Sep 19, 2011 at 02:53:33PM +0200, Michal Hocko wrote:
    > > Hi,
    > >
    > > On Mon 12-09-11 12:57:18, Johannes Weiner wrote:
    > > > Memory control groups are currently bolted onto the side of
    > > > traditional memory management in places where better integration would
    > > > be preferrable. To reclaim memory, for example, memory control groups
    > > > maintain their own LRU list and reclaim strategy aside from the global
    > > > per-zone LRU list reclaim. But an extra list head for each existing
    > > > page frame is expensive and maintaining it requires additional code.
    > > >
    > > > This patchset disables the global per-zone LRU lists on memory cgroup
    > > > configurations and converts all its users to operate on the per-memory
    > > > cgroup lists instead. As LRU pages are then exclusively on one list,
    > > > this saves two list pointers for each page frame in the system:
    > > >
    > > > page_cgroup array size with 4G physical memory
    > > >
    > > > vanilla: [ 0.000000] allocated 31457280 bytes of page_cgroup
    > > > patched: [ 0.000000] allocated 15728640 bytes of page_cgroup
    > > >
    > > > At the same time, system performance for various workloads is
    > > > unaffected:
    > > >
    > > > 100G sparse file cat, 4G physical memory, 10 runs, to test for code
    > > > bloat in the traditional LRU handling and kswapd & direct reclaim
    > > > paths, without/with the memory controller configured in
    > > >
    > > > vanilla: 71.603(0.207) seconds
    > > > patched: 71.640(0.156) seconds
    > > >
    > > > vanilla: 79.558(0.288) seconds
    > > > patched: 77.233(0.147) seconds
    > > >
    > > > 100G sparse file cat in 1G memory cgroup, 10 runs, to test for code
    > > > bloat in the traditional memory cgroup LRU handling and reclaim path
    > > >
    > > > vanilla: 96.844(0.281) seconds
    > > > patched: 94.454(0.311) seconds
    > > >
    > > > 4 unlimited memcgs running kbuild -j32 each, 4G physical memory, 500M
    > > > swap on SSD, 10 runs, to test for regressions in kswapd & direct
    > > > reclaim using per-memcg LRU lists with multiple memcgs and multiple
    > > > allocators within each memcg
    > > >
    > > > vanilla: 717.722(1.440) seconds [ 69720.100(11600.835) majfaults ]
    > > > patched: 714.106(2.313) seconds [ 71109.300(14886.186) majfaults ]
    > > >
    > > > 16 unlimited memcgs running kbuild, 1900M hierarchical limit, 500M
    > > > swap on SSD, 10 runs, to test for regressions in hierarchical memcg
    > > > setups
    > > >
    > > > vanilla: 2742.058(1.992) seconds [ 26479.600(1736.737) majfaults ]
    > > > patched: 2743.267(1.214) seconds [ 27240.700(1076.063) majfaults ]
    > >
    > > I guess you want to have this in the first patch to have it for
    > > reference once it gets to the tree, right? I have no objections but it
    > > seems unrelated to the patch and so it might be confusing a bit. I
    > > haven't seen other patches in the series so there is probably no better
    > > place to put this.
    >
    > Andrew usually hand-picks what's of long-term interest from the series
    > description and puts it in the first patch. I thought I'd save him
    > the trouble.

    Understood

    [...]

    > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > > > index b76011a..912c7c7 100644
    > > > --- a/mm/memcontrol.c
    > > > +++ b/mm/memcontrol.c
    > > > @@ -781,83 +781,75 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
    > > > return memcg;
    > > > }
    > > >
    > > > -/* The caller has to guarantee "mem" exists before calling this */
    > >
    > > Shouldn't we have a similar comment that we have to keep a reference to
    > > root if non-NULL. A mention about remember parameter and what is it used
    > > for (hierarchical reclaim) would be helpful as well.
    >
    > The only thing that dictates the lifetime of a memcg is its reference
    > count, so having a reference count while operating on a memecg is not
    > even a question for all existing memcg-internal callsites.

    Fair enough.

    >
    > But I did, in fact, add kernel-doc style documentation to
    > mem_cgroup_iter() when it becomes a public interface in 5/11. Can you
    > take a look and tell me whether you are okay with that?

    OK, I will comment on that patch once I get to it.

    [...]

    Thanks!
    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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