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SubjectRe: Possible Bug in VM accounting (Committed_AS) on x86_64 architecture ?
Hi,
I am running into a problem and due to limited understanding unable to
solve it...
Problem:
-------------
On 64 bit machines (running linux 2.6.xx), Committed_AS grows over the
period of time. Within 3-4 weeks system reaches a stage where further
malloc() returns -ENOMEM. Test shows that just running simple program
(which malloc, touch, free memory) cause this increase in Committed_AS
number. (I am using vm-overcommit... Below detailed information)

System/Kernel Spec:
------------------------------
-----
CentOS kernel, 2.6.9-34.EL-x86_64_SMP
Physical: 8G
Swap: 2G
Machine type: AMD
Nothing un-usual in .config. Pretty much using standard options. (If
needed I will send .config)
Here is /proc/meminfo numbers:

MemTotal: 8169736 kB
MemFree: 1256676 kB
Buffers: 123496 kB
Cached: 5009620 kB
SwapCached: 0 kB
Active: 5297288 kB
Inactive: 1003628 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 8169736 kB
LowFree: 1256676 kB
SwapTotal: 2096472 kB
SwapFree: 2096472 kB
Dirty: 10036 kB
Writeback: 0 kB
Mapped: 5814464 kB
Slab: 571352 kB
Committed_AS: 7125024 kB
PageTables: 12916 kB
VmallocTotal: 536870911 kB
VmallocUsed: 268300 kB
VmallocChunk: 536601679 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 2048 kB

OverCommit Options:
---------------------------------
vm.overcommit_ratio = 100
vm.overcommit_memory = 2

Hence my virtual limit is 10G (8*100/100 + 2)

Detailed Description:
-------------------------------
I have noticed that 64 bit machine with overcommit policy (as above)
starts giving problem within 3-4 weeks. To prove that I've written
small program.
It allocates memory of different sizes (not that it matters much due
to caching of diffeent malloc. I am using standard ptmalloc). Sizes
are 16B, 32B, 64B, 256B, 1024B, 57B, 127B and so on... . Then it
touches that memory (memset) and then free it. These operations are
being performed in while(1) loop.

Observations:
----------------------
Committed_AS: number gorws 5M per hour. I made sure that nothing else
is running on the system during that time...

Is there any obvious problem reported for vm accounting on 64 bit
architecture ? Or this is expected ? Or vm-overcommit is only meant
for 32 bit architecture ?

Please advice..

Thanks in advance.
--

-Kunal
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