On 04/24/2012 07:54 PM, David Rientjes wrote:
On Tue, 24 Apr 2012, Glauber Costa wrote:
Yes, for user memory, I see charging to p->mm->owner as allowing that
process to eventually move and be charged to a different memcg and there's
no way to do proper accounting if the charge is split amongst different
memcgs because of thread membership to a set of memcgs. This is
consistent with charges for shared memory being moved when a thread
mapping it moves to a new memcg, as well.
But that's the problem.
When we are dealing with kernel memory, we are allocating a whole slab page.
It is essentially impossible to track, given a page, which task allocated
which object.
Right, so you have to make the distinction that slab charges cannot be
migrated by memory.move_charge_at_immigrate (and it's not even specified
to do anything beyond user pages in Documentation/cgroups/memory.txt),
Never intended to.
but
it would be consistent to charge the same memcg for a process's slab
allocations as the process's user allocations.
My response was why we shouldn't be charging user pages to
mem_cgroup_from_task(current) rather than
mem_cgroup_from_task(current->mm->owner) which is what is currently
implemented.
Ah, all right. Well, for user memory I agree with you. My point was
exactly that user memory can always be pinpointed to a specific address
space, while kernel memory can't.
If that can't be changed so that we can still migrate user memory amongst
memcgs for memory.move_charge_at_immigrate, then it seems consistent to
have all allocations done by a task to be charged to the same memcg.
Hence, I suggested current->mm->owner for slab charging as well.
All right. This can be done. Although I don't see this as a must for
slab as already explained, I certainly don't oppose doing so as well.
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