Re: quicklists confuse meminfo
- From: Ingo Molnar <mingo@xxxxxxx>
- Date: Sun, 9 Mar 2008 12:14:56 +0100
* Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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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