Sorry for not sending this to linux-mm,
but I can't subscribe at present? Anyway...
I wrote the following script to try and accurately determine
how much RAM a particular program uses:
http://www.pixelbeat.org/scripts/ps_mem.py
A user reported an issue on debian with kernel 2.6.8-2-386
where many processes were being reported as using
a negative amount of memory.
I asked him to run the following:
(
echo total rss shared trs - drs -
for pid in `pidof apache2`; do
cat /proc/$pid/statm
done
) | column -t
the output of which was:
total rss shared trs - drs -
6580 2306 5273 95 0 6485 0
6580 2313 5273 95 0 6485 0
6119 1717 5269 95 0 6024 0
6630 2371 5273 95 0 6535 0
6735 2503 5273 95 0 6640 0
6773 2546 5273 95 0 6678 0
5845 1146 5198 95 0 5750 0
Notice the large values for the shared column.
Also notice that the shared column is larger than rss!?
I had assumed that shared was a subset of rss from
the following (pseudo) code from fs/proc/task_mmu.c::task_statm()
*total = mm->total_em
*shared = get_mm_counter(mm, file_rss)
*rss = *shared + get_mm_counter(mm, anon_rss)
*trs = mm->end_code - mm->start_code
*drs = mm->total_vm - mm->shared_vm
Therefore anon_rss must be negative in the kernel?
So there is a mismatch between pages being marked
as anonymous and anon_rss being updated appropriately?
cheers,
Pádraig.
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