Re: [RFC][PATCH] update /proc/sys/vm/drop_caches documentation

[Eric W. Biederman]

Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> writes:

> On Wed, 2010-09-15 at 11:37 -0700, Eric W. Biederman wrote:
>> > I'm worried that there are users out there experiencing real problems
>> > that aren't reporting it because "workarounds" like this just paper over
>> > the issue.
>> 
>> For what it is worth.  I had a friend ask me about a system that had 50%
>> of it's memory consumed by slab caches.  20GB out of 40GB.  The kernel
>> was suse? 2.6.27 so it's old, but if you are curious.
>> /proc/sys/vm/drop_caches does nothing in that case. 
>
> Was it the reclaimable caches doing it, though?  The other really common
> cause is kmalloc() leaks.

It was reclaimable caches.  He kept seeing the cache sizes of the
problem caches shrink.  On an idle system he said he was seeing
about 16MB/min getting free or something like that.  Something
that would take hours and hours before things freed up.

I asked and my friend told me that according to slabtop the slab
with the most memory used kept changing dramatically and he could
not see a pattern.

So at least on one old kernel on one strange workload there was a problem.

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