Messages in this thread | | | Date | Thu, 11 Sep 2008 10:50:44 -0700 | From | "Paul Menage" <> | Subject | Re: [RFC PATCH -mm 2/2] cgroup: fold struct cg_cgroup_link into struct css_set |
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On Thu, Sep 11, 2008 at 7:23 AM, Lai Jiangshan <laijs@cn.fujitsu.com> wrote: > > one struct cg_cgroup_link per link is very waste. > This way need to allocate struct cg_cgroup_link for > (css_set_count * hierarchy_count) times.
Correct - but in the common case, hierarchy_count==1. So it's 7 pointers (two list_heads and a pointer in the cg_cgroup_link, and a list_head in the css_set) per css_set. Each additional hierarchy introduces 5 pointers per css_set with the new cg_cgroup_link. (So overall, 2 + 5*H)
We're up to 9 cgroup subsystems in -mm right now, so your approach consumes 18 pointers (9 list heads) per css_set, regardless of how many hierarchies are mounted.
So I think that the current solution saves memory when there are fewer than four hierarchies mounted. As the number of cgroup subsystems increases, the break-even point will increase. I expect that the most common number of mounted hierarchies will be 0 (but there's only one css_set in that case, so the overhead is irrelevant) or 1.
> > This patch removes lots of line of code. remove struct cg_cgroup_link > and corresponding code.
Yes, the code is definitely simpler after your patch. It's pretty much how it was *before* I introduced the cg_cgroup_link structures to allow an arbitrary number of hierarchies without bloating the css_set structure. I'm not convinced that we want to go back to the original way.
Paul
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