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    SubjectRe: cgroup: rmdir() does not complete
    On Fri, 10 Sep 2010, KAMEZAWA Hiroyuki wrote:

    > On Fri, 10 Sep 2010 08:28:00 +0100 (BST)
    > Mark Hills <mark@pogo.org.uk> wrote:
    >
    > > On Fri, 10 Sep 2010, KAMEZAWA Hiroyuki wrote:
    > >
    > > > On Fri, 10 Sep 2010 00:04:31 +0100 (BST)
    > > > Mark Hills <mark@pogo.org.uk> wrote:
    > > > > The report on the spinning process (23586) is dominated by calls from
    > > > > mem_cgroup_force_empty.
    > > > >
    > > > > It seems to show lru_add_drain_all and drain_all_stock_sync are causing
    > > > > the load (I assume drain_all_stock_sync has been optimised out). But I
    > > > > don't think this is as important as what causes the spin.
    > > > >
    > > >
    > > > I noticed you use FUSE and it seems there is a problem in FUSE v.s. memcg.
    > > > I wrote a patch (onto 2.6.36 but can be applied..)
    > > >
    > > > Could you try this ? I'm sorry I don't use FUSE system and can't test
    > > > right now.
    > >
    > > What makes you conclude that FUSE is in use? I do not think this is the
    > > case. Or do you mean that it is a problem that the kernel is built with
    > > FUSE support?
    > >
    > You wrote
    > > The test case I was running is similar to the above. With the Lustre
    > > filesystem the problem takes 4 hours or more to show itself. Recently I
    > > ran 4 threads for over 24 hours without it being seen -- I suspect some
    > > external factor is involved.
    >
    > I think Lustre FS is using FUSE. I'm wrong ?

    Lustre does not use FUSE. But the client is a set of kernel modules, so
    these could do anything.

    > > I _can_ test the patch, but I still cannot reliably reproduce the problem
    > > so it will be hard to conclude whether the patch works or not. Is there a
    > > way to build a test case for this?
    > >
    >
    > I'm sorry I'm not sure yet. But from your report, you have 6 pages of charge
    > which cannot be found by force_empty(). And I found FUSE's pipe copy code
    > inserts a page cache into radix-tree but not move them onto LRU.
    >
    > So,
    > - There are remaining pages which is out-of-LRU
    > - FUSE's "move" code does something curious, add_to_page_cache() but not LRU.
    > - You reporeted you use Lustre FS.
    >
    > Then, I ask you. To test this, I have to study FUSE to write test module...
    > Maybe adding printk() to where I added gfp_mask modification of fuse/dev.c
    > can show something but...
    >
    > We may have something other problem, but it seems this is one of them.

    Okay, it sounds like perhaps I need to investigate Lustre, I will do this
    next week. But I think FUSE can be ruled out.

    Thanks again

    --
    Mark


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