On Wed, 26 Jan 2011 14:29:09 -0800 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 26 Jan 2011 12:32:04 -0800 > Greg Thelen <gthelen@xxxxxxxxxx> 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. > I think we can assume that. > 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? > I'll review. Against the roll-over, I think we just need to take lock. So, res_counter_read_u64() implementation was wrong. It should take lock. Please give me time. THanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>