Messages in this thread | | | Date | Tue, 3 Feb 2009 14:49:15 -0800 | Subject | Re: [PATCH] cpuset: fix allocating page cache/slab object on the unallowed node when memory spread is set | From | Paul Menage <> |
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On Tue, Feb 3, 2009 at 2:16 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Tue, 03 Feb 2009 11:25:25 +0800 > Miao Xie <miaox@cn.fujitsu.com> wrote: > >> on 2009-1-28 6:42 Andrew Morton wrote: >> > On Wed, 21 Jan 2009 16:06:20 +0800 >> > Miao Xie <miaox@cn.fujitsu.com> wrote: >> > >> >> The task still allocated the page caches on old node after modifying its >> >> cpuset's mems when 'memory_spread_page' was set, it is caused by the old >> >> mem_allowed_list of the task, the current kernel doesn't updates it unless some >> >> function invokes cpuset_update_task_memory_state(), it is too late sometimes. >> >> We must update the mem_allowed_list of the tasks in time. >> >> >> >> Slab has the same problem. >> >> >> >> We fixes the bug by updating tasks' mem_allowed_list and spread flag after >> >> its cpuset's mems or spread flag is changed. >> >> >> >> >> >> ... >> >> >> >> --- a/kernel/kthread.c >> >> +++ b/kernel/kthread.c >> >> @@ -242,6 +242,7 @@ int kthreadd(void *unused) >> >> set_user_nice(tsk, KTHREAD_NICE_LEVEL); >> >> set_cpus_allowed_ptr(tsk, CPU_MASK_ALL_PTR); >> >> >> >> + current->mems_allowed = node_possible_map; >> >> current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG; >> > >> > Why this change? kthreadd() is called from rest_init(), before anyone >> > has had a chance to alter ->mems_allowed? >> >> I found that after mems_allowed of kthreadd was not initialized applying this patch, >> every bit of it is 1, so... >> Maybe it is redundant. > > I think it is redundant. kthreadd's mems_allowed _should_ be all-ones. > Or at least, all-nodes-allowed. > > I wasn't able to find out where the setting of init'smems_allowed > happens, after a bit of grepping and hunting. It should be done within > INIT_TASK, but isn't. > > Still, kthreadd is reliably parented by swapper, and there shold be no > need to alter its mems_allowed. > > Similarly, what was the reason for setting current->mems_allowed in > kernel_init()? That also should be unneeded. > > Finally, I've somewhat lost track of where we are with this patch. > Paul, do you see any other remaining issues?
AFAICS this patch still has a race between a thread reading its mems_allowed, and another thread updating it. The current architecture of having task->mems_allowed be only updatable by current was PaulJ's code originally, and I'm a bit loathe to touch it. But if we're going to, we'll need at the minimum to add a lock for any code that touches current->mems_allowed.
Paul
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