[ale] Free is not showing me correct used memory
Jim Kinney
jim.kinney at gmail.com
Sat Aug 22 10:56:13 EDT 2020
When did memory over commit become safely possible? I don't have to dig often into details of memory management but sometime in kernel 2 days a major change occured. Memory was marked allocated when requested regardless of use. But a different request process was used to report use. The overcommit allowed unused but allocated memory to be used by another process. The change merged those two or clarified or something. Been a long time. I also vaguely recall there might have been a race condition in the first few iterations of the change. Something to do with a thread problem and the over commit not playing well together.
On August 22, 2020 10:30:01 AM EDT, Chris Fowler <cfowler at outpostsentinel.com> wrote:
>
>When I copied that program from the web page I noticed something odd,
>but did not question it.
>
>memset(b, TEN_MB, 0);
>
>The size argument is the last one! It should've been. As many times
>that I've used memset() I should have corrected it the first time.
>Just me being an idiot and not second guessing someone else's program.
>
>memset(b, 0x0, TEN_MB);
>
>[root at basement]# free
> total used free shared buffers cached
>Mem: 1964784 1225620 739164 0 5108 24632
>-/+ buffers/cache: 1195880 768904
>Swap: 524284 0 524284
>
>Now I'd like to ask the stupid question of why does Linux consider
>memory allocated via malloc(), but not used not good enough to mark
>that memory as used for /proc/meminfo? I can't mallco() anymore
>anyway. This is why watchdog's active test of trying to allocate
>memory is better than its passive test of just groking /poc/memifno.
>
>________________________________
>From: Jim Kinney <jim.kinney at gmail.com>
>Sent: Friday, August 21, 2020 10:20 PM
>To: Chris Fowler <cfowler at outpostsentinel.com>; Atlanta Linux
>Enthusiasts <ale at ale.org>
>Subject: Re: [ale] Free is not showing me correct used memory
>
>Is your ram fully functional? Memtest results are 100% perfect?
>
>Cgroups can direct oomkiller to odd locations.
>
>Strange problem.
>
>On August 21, 2020 8:33:17 PM EDT, Chris Fowler via Ale <ale at ale.org>
>wrote:
>I just enabled 500M of swap on the device, but it does not use disk. I
>uses a zram device. The kernel configured 500M of compressed ram for
>the use of swap. The oom program was able to grab 134 chunks before
>watchdog restarted. That's 1.3G. Is my kernel config wrong?
>
>Chris
>________________________________
>From: Ale <ale-bounces at ale.org> on behalf of Chris Fowler via Ale
><ale at ale.org>
>Sent: Friday, August 21, 2020 8:16 PM
>To: ALE <ale at ale.org>
>Subject: [ale] Free is not showing me correct used memory
>
>I've ran into an issue on a device which runs out of memory, but it
>refuses to panic on OOM. This creates a DOS affect. No SSH to the
>device, but I am still able to ping it. After reboot messages in syslog
>show the device has ran out of memory. Kernel is 2.,6.38 and system is
>32bit.
>
>I followed instructions on the URL below to test OOM panic. I compiled
>an ran the program to test. On a system with kernel 5.6.0 the OOM
>panics and system is restarted. It works, but on the problem device it
>is as if the OOM is not fully aware. free, /proc/meminfo, vmstat, etc
>do not show memory usage skyrocketing as it does on the other system.
>
>Free on the problem device before I run the program:
>
>[root at basement]# free
> total used free shared buffers cached
>Mem: 1964728 235380 1729348 0 12064 55388
>-/+ buffers/cache: 167928 1796800
>Swap: 0 0 0
>
>Now, I run it and it is able to allocate 82 chunks at 10M each before
>malloc() failed:
>
>[root at basement]# oom
>Allocated 82 chunks.
>Sleeping 60(s) before exiting.
>
>In another xterm I'll run free while oom is waiting to exit. Once it
>exits, all that memory is freed. No change.
>
>[root at basement]# free
> total used free shared buffers cached
>Mem: 1964728 236380 1728348 0 12112 55388
>-/+ buffers/cache: 168880 1795848
>Swap: 0 0 0
>
>If I run oom in another window it will only grab 2 chunks before
>failure. Also, watchdog is configured to restart if it can't allocate
>20M of memory. Watchdog will restart the device because it is unable
>to grab it.
>
>The system itself has 2G of RAM.
>
>If that program was able to allocate 82x10 820M of RAM why did that not
>show up as used memory? Now, I'm curious as to why Iw as only able to
>allocate 830M if there is 1.7GB free?
>
>Below is grep 'MEM' config:
>
># CONFIG_CGROUP_MEM_RES_CTLR is not set
>CONFIG_SHMEM=y
>CONFIG_X86_SUPPORTS_MEMORY_FAILURE=y
>CONFIG_NO_BOOTMEM=y
># CONFIG_MEMTEST is not set
># CONFIG_NOHIGHMEM is not set
>CONFIG_HIGHMEM4G=y
># CONFIG_HIGHMEM64G is not set
>CONFIG_HIGHMEM=y
>CONFIG_ARCH_FLATMEM_ENABLE=y
>CONFIG_ARCH_SPARSEMEM_ENABLE=y
>CONFIG_ARCH_SELECT_MEMORY_MODEL=y
>CONFIG_SELECT_MEMORY_MODEL=y
>CONFIG_FLATMEM_MANUAL=y
># CONFIG_SPARSEMEM_MANUAL is not set
>CONFIG_FLATMEM=y
>CONFIG_FLAT_NODE_MEM_MAP=y
>CONFIG_SPARSEMEM_STATIC=y
>CONFIG_HAVE_MEMBLOCK=y
>CONFIG_ARCH_SUPPORTS_MEMORY_FAILURE=y
># CONFIG_MEMORY_FAILURE is not set
>CONFIG_X86_BOOTPARAM_MEMORY_CORRUPTION_CHECK=y
>CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y
># CONFIG_BLK_DEV_UMEM is not set
>CONFIG_INPUT_FF_MEMLESS=y
>CONFIG_DEVKMEM=y
>CONFIG_FIX_EARLYCON_MEM=y
># CONFIG_HW_RANDOM_TIMERIOMEM is not set
># CONFIG_MEMSTICK is not set
>CONFIG_FIRMWARE_MEMMAP=y
># CONFIG_DEBUG_KMEMLEAK is not set
># CONFIG_DEBUG_HIGHMEM is not set
># CONFIG_DEBUG_MEMORY_INIT is not set
>CONFIG_HAVE_ARCH_KMEMCHECK=y
># CONFIG_STRICT_DEVMEM is not set
>CONFIG_ASYNC_MEMCPY=y
>CONFIG_HAS_IOMEM=y
>
>Also:
>
>CONFIG_VMSPLIT_3G=y
># CONFIG_VMSPLIT_3G_OPT is not set
># CONFIG_VMSPLIT_2G is not set
># CONFIG_VMSPLIT_2G_OPT is not set
># CONFIG_VMSPLIT_1G is not set
>CONFIG_PAGE_OFFSET=0xC0000000
>
>
>--
>"no government by experts in which the masses do not have the chance to
>inform the experts as to their needs can be anything but an oligarchy
>managed in the interests of the few.” - John Dewey
--
"no government by experts in which the masses do not have the chance to inform the experts as to their needs can be anything but an oligarchy managed in the interests of the few.” - John Dewey
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