Messages in this thread |  | | | Date | Wed, 26 Jan 2011 14:29:09 -0800 | | From | Andrew Morton <> | | Subject | Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory() |
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On Wed, 26 Jan 2011 12:32:04 -0800 Greg Thelen <gthelen@google.com> wrote:
> > That being said, does this have any practical impact at all? I mean, > > this code runs when the cgroup limit is breached. But if the number > > of allowed pages (not bytes!) can not fit into 32 bits, it means you > > have a group of processes using more than 16T. On a 32-bit machine. > > The value of this patch is up for debate. I do not have an example > situation where this truncation causes the wrong thing to happen. I > suppose it might be possible for a racing update to > memory.limit_in_bytes which grows the limit from a reasonable (example: > 100M) limit to a large limit (example 1<<45) could benefit from this > patch. I admit that this case seems pathological and may not be likely > or even worth bothering over. If neither the memcg nor the oom > maintainers want the patch, then feel free to drop it. I just noticed > the issue and thought it might be worth addressing.
Ah. I was scratching my head over that.
In zillions of places the kernel assumes that a 32-bit kernel has less than 2^32 pages of memory, so the code as it stands is, umm, idiomatic.
But afaict the only way the patch makes a real-world difference is if res_counter_read_u64() is busted?
And, as you point out, res_counter_read_u64() is indeed busted on 32-bit machines. It has 25 callsites in mm/memcontrol.c - has anyone looked at the implications of this? What happens in all those callsites if the counter is read during a count rollover?
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