Re: [PATCH 1/6] AKT - Tunable structure and registration routines

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Andi Kleen wrote:
[email protected] writes:

+
+This feature aims at making the kernel automatically change the tunables
+values as it sees resources running out.


The only reason we have resource limit is to avoid DOS when one
resource consumes too much memory.  When there is no such danger then
there isn't any reason to have a limit at all and it could be just
eliminated (or set to unlimited by default)

Automatic tuning is a way to set the limit to unlimited, in a sense, doesn't it? With this feature, we can leave the default limits as they are for an "every-day" usage, and when a particular application runs on the machine, authorize the limit to grow up as needed.


Your feature doesn't address the DOS and without that there isn't
any reason to have limits at all. So what's the point?

As I told Eric Biederman in another mail, DoS in ensured in AKT by exporting the min and max values for each tunable to sysfs (actually Eric complained about these min and max :-( ). These are RW atrributes that make it possible for a sysadmin to set the max value a tunable can ever reach, instead of letting it grow up to huge values.


I agree that some of the default limits we have are not very useful
on modern machines. I guess you're trying to address that.

Yep


I would suggest the following strategy:

- Review any limits we have and make sure they make sense.

- Figure out if they actually serve a useful purpose e.g. what happens when they are exceeded, is there a DOS?. If yes can the DOS be addressed in a better way (e.g. by allowing to shrink
the resource by a shrinker callback).
Some of the existing limits are clearly bogus, e.g. the limit
on shared memory.

For others i don't see a good alternative. e.g. if you don't limit
the number of files allocated the only alternative would be to kill
processes when they allocate too many files. Is that really preferable
to a errno?

Agree with you, BUT between the default max_files and the "too many files" situation, there is a gap that can be crossed by automatically tuning max_files, isn't there? e.g. max_file default value is NR_FILE (0x2000), while Oracle expects to have it set to 0x10000.


- If they serve a useful purpose then check if the default is useful
on a modern machine. Or make them scale with the amount of memory
like many limits already do.

-Andi


Regards,
Nadia

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux