Messages in this thread | | | Date | Sun, 7 Apr 2013 11:32:48 +0800 | From | Li Zefan <> | Subject | Re: [RFC][PATCH 2/7] memcg: don't use mem_cgroup_get() when creating a kmemcg cache |
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>>> You are putting references but I do not see any single css_{try}get >>> here. /me puzzled. >>> >> >> There are two things being done in this code: >> First, we acquired a css_ref to make sure that the underlying cgroup >> would not go away. That is a short lived reference, and it is put as >> soon as the cache is created. >> At this point, we acquire a long-lived per-cache memcg reference count >> to guarantee that the memcg will still be alive. >> >> so it is: >> >> enqueue: css_get >> create : memcg_get, css_put >> destroy: css_put >> >> If I understand Li's patch correctly, he is not touching the first >> css_get, only turning that into the long lived reference (which was not >> possible before, since that would prevent rmdir). >> >> Then he only needs to get rid of the memcg_get, change the memcg_put to >> css_put, and get rid of the now extra css_put. >> >> He is issuing extra css_puts in memcg_create_kmem_cache, but only in >> failure paths. So the code reads as: >> * css_get on enqueue (already done, so not shown in patch) >> * if it fails, css_put >> * if it succeeds, don't do anything. This is already the long-lived >> reference count. put it at release time. > > OK, this makes more sense now. It is __memcg_create_cache_enqueue which > takes the reference and it is not put after this because it replaced > mem_cgroup reference counting. > Li, please put something along these lines into the changelog. This is > really tricky and easy to get misunderstand. >
Yeah, I think I'll just steal Glauber's explanation as the changelog.
> You can put my Acked-by then. >
Thanks!
>> The code looks correct, and of course, extremely simpler due to the >> use of a single reference. >> >> Li, am I right in my understanding that this is your intention? >>
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