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SubjectRe: quicklists confuse meminfo

* Thomas Gleixner <tglx@linutronix.de> wrote:

> Bart reported http://bugzilla.kernel.org/show_bug.cgi?id=9991. He
> assumed a memory leak in 32bit kernels when he analyzed the output of
> /proc/meminfo.
>
> The leak is not a leak, it's an accounting bug. quicklists keep a
> large amount of pages which are accounted as used memory.
[...]
> Another strange observation about quicklists is the imbalance of the
> quicklists across CPUs. Running the above loop on a 2way machine I can
> observe that the quicklist pages are acuumulating on one CPU. Stopping
> and restarting the loop a couple of times can shift the accumulation
> from one to the other CPU.

hm. I think we should not let this much RAM hang around in a
special-purpose allocator like quicklists. Shouldnt the quicklists be
temporary in nature, and be trimmed much more agressively?

in fact, we have a check_pgt_cache() call in cpu_idle(), which does:

quicklist_trim(0, pgd_dtor, 25, 16);

but it appears we dont do quicklist trimming anywhere else! So if a
system has no idle time, the quicklist can grow unbounded, and that's a
real memory leak IMO.

Ingo


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