top shows only part of available physmem
Bartosz Stec
bartosz.stec at it4pro.pl
Fri Jan 28 10:38:03 UTC 2011
>>>>>>>>> Guys,
>>>>>>>>>
>>>>>>>>> could someone explain me this?
>>>>>>>>>
>>>>>>>>> # sysctl hw.realmem
>>>>>>>>> hw.realmem: 2139029504
>>>>>>>>>
>>>>>>>>> top line shows:
>>>>>>>>>
>>>>>>>>> Mem: 32M Active, 35M Inact, 899M Wired, 8392K Cache,
>>>>>>>>> 199M Buf, 58M Free
>>>>>>>>>
>>>>>>>>> 32+35+899+8+199+58 = 1231MB
>>>>>>>>>
>>>>>>>>> Shouldn't that sum to all available ram? Or maybe I'm reading
>>>>>>>>> it wrong?
>>>>>>>>> This machine has indeed 2GB of ram on board and showed in BIOS.
>>>>>>>>> i386 FreeBSD 8.2-PRERELEASE #16: Mon Jan 17 22:28:53 CET 2011
>>>>>>>>> Cheers.
>>>>>>>> First, don't include 'buf' as isn't a separate set of RAM, it
>>>>>>>> is only a range
>>>>>>>> of the virtual address space in the kernel. It used to be
>>>>>>>> relevant when the
>>>>>>>> buffer cache was separate from the VM page cache, but now it is
>>>>>>>> mostly
>>>>>>>> irrelevant (arguably it should just be dropped from top output).
>>>>>>> Thanks for the explanation. So 1231MB - 199MB Buf and we got
>>>>>>> about 1GB
>>>>>>> of memory instead of 2B.
>>>>>>>
>>>>>>>> However, look at what hw.physmem says (and the realmem and
>>>>>>>> availmem lines in
>>>>>>>> dmesg). realmem is actually not that useful as it is not a
>>>>>>>> count of the
>>>>>>>> amount of memory, but the address of the highest memory page
>>>>>>>> available. There
>>>>>>>> can be less memory available than that due to "holes" in the
>>>>>>>> address space for
>>>>>>>> PCI memory BARs, etc.
>>>>>>>>
>>>>>>> OK, here you go:
>>>>>>> # sysctl hw | grep mem
>>>>>>>
>>>>>>> hw.physmem: 2125893632
>>>>>>> hw.usermem: 1212100608
>>>>>>> hw.realmem: 2139029504
>>>>>>> hw.pci.host_mem_start: 2147483648
>>>>>> Humm, you should still have 2GB of RAM then. All the memory you
>>>>>> set aside
>>>>>> for ARC should be counted in the 'wired' count, so I'm not sure
>>>>>> why you see
>>>>>> 1GB of RAM rather than 2GB.
>>>>> For what its worth (seems to be the same values top shows), the
>>>>> sysctl's
>>>>> I use to make cacti graphs of memory usage are: (Counts are in pages)
>>>>>
>>>>> vm.stats.vm.v_page_size
>>>>>
>>>>> vm.stats.vm.v_wire_count
>>>>> vm.stats.vm.v_active_count
>>>>> vm.stats.vm.v_inactive_count
>>>>> vm.stats.vm.v_cache_count
>>>>> vm.stats.vm.v_free_count
>>>>>
>>>>> Using the output of those sysctls I allways get a cacti graph
>>>>> which at
>>>>> least very much seems to account for all memory, and has a flat
>>>>> surface
>>>>> in a stacked graph.
>>>> These sysctls are exactly what top uses. There is also a
>>>> 'v_page_count'
>>>> which is a total count of pages.
>>>>
>>> So here's additional sysctl output from now:
>>>
>>> fbsd# sysctl hw | grep mem
>>> hw.physmem: 2125893632
>>> hw.usermem: 1392594944
>>> hw.realmem: 2139029504
>>> hw.pci.host_mem_start: 2147483648
>>>
>>> fbsd# sysctl vm.stats.vm
>>> vm.stats.vm.v_kthreadpages: 0
>>> vm.stats.vm.v_rforkpages: 0
>>> vm.stats.vm.v_vforkpages: 1422927
>>> vm.stats.vm.v_forkpages: 4606557
>>> vm.stats.vm.v_kthreads: 40
>>> vm.stats.vm.v_rforks: 0
>>> vm.stats.vm.v_vforks: 9917
>>> vm.stats.vm.v_forks: 30429
>>> vm.stats.vm.v_interrupt_free_min: 2
>>> vm.stats.vm.v_pageout_free_min: 34
>>> vm.stats.vm.v_cache_max: 27506
>>> vm.stats.vm.v_cache_min: 13753
>>> vm.stats.vm.v_cache_count: 20312
>>> vm.stats.vm.v_inactive_count: 18591
>>> vm.stats.vm.v_inactive_target: 20629
>>> vm.stats.vm.v_active_count: 1096
>>> vm.stats.vm.v_wire_count: 179027
>>> vm.stats.vm.v_free_count: 6193
>>> vm.stats.vm.v_free_min: 3260
>>> vm.stats.vm.v_free_target: 13753
>>> vm.stats.vm.v_free_reserved: 713
>>> vm.stats.vm.v_page_count: 509752
>>> vm.stats.vm.v_page_size: 4096
>>> vm.stats.vm.v_tfree: 196418851
>>> vm.stats.vm.v_pfree: 2837177
>>> vm.stats.vm.v_dfree: 0
>>> vm.stats.vm.v_tcached: 1305893
>>> vm.stats.vm.v_pdpages: 3527455
>>> vm.stats.vm.v_pdwakeups: 187
>>> vm.stats.vm.v_reactivated: 83786
>>> vm.stats.vm.v_intrans: 3053
>>> vm.stats.vm.v_vnodepgsout: 134384
>>> vm.stats.vm.v_vnodepgsin: 29213
>>> vm.stats.vm.v_vnodeout: 96249
>>> vm.stats.vm.v_vnodein: 29213
>>> vm.stats.vm.v_swappgsout: 19730
>>> vm.stats.vm.v_swappgsin: 8573
>>> vm.stats.vm.v_swapout: 5287
>>> vm.stats.vm.v_swapin: 2975
>>> vm.stats.vm.v_ozfod: 83338
>>> vm.stats.vm.v_zfod: 2462557
>>> vm.stats.vm.v_cow_optim: 330
>>> vm.stats.vm.v_cow_faults: 1239253
>>> vm.stats.vm.v_vm_faults: 5898471
>>>
>>> fbsd# sysctl vm.vmtotal
>>> vm.vmtotal:
>>> System wide totals computed every five seconds: (values in
>>> kilobytes)
>>> ===============================================
>>> Processes: (RUNQ: 1 Disk Wait: 0 Page Wait: 0
>>> Sleep: 60)
>>> Virtual Memory: (Total: 4971660K Active: 699312K)
>>> Real Memory: (Total: 540776K Active: 29756K)
>>> Shared Virtual Memory: (Total: 41148K Active: 19468K)
>>> Shared Real Memory: (Total: 4964K Active: 3048K)
>>> Free Memory Pages: 105308K
>>>
>>>
>>> /usr/bin/top line: Mem: 4664K Active, 73M Inact, 700M Wired, 79M
>>> Cache, 199M Buf, 23M Free
>>> Sum (Without Buf): 879,5 MB
>>>
>>> So what are we looking at? Wrong sysctls/top output or maybe
>>> actually FreeBSD doesn't use all available RAM for some reason?
>>> Could it be hardware problem? Maybe I should provide some
>>> additional
>>> data?
>> Does the behaviour become more expected if you remove ZFS from the
>> picture? Please try this (yes really).
>>
> About an hour ago I had to hard reset this machine because it stopped
> responding (bu still gived ping response) after massive slowdown seen
> by SAMBA users.
> Now top shows following:
> Mem: 78M Active, 83M Inact, 639M Wired, 120K Cache, 199M Buf, 1139M Free.
>
> What I am afraid is that this PC slowly eats own memory and finally
> starved itself to death, because it happened second time in 2 weeks,
> and it seems that rebuilding world+kernel Mon Jan 17 22:28:53 CET 2011
> could be the cause. For some strange reason I believe that Jeremy
> Chadwick could be right pointing ZFS. Way this machine stops
> responding without any info in logs makes me believe that it has
> simply lost ability to I/O to HDD (system is ZFS-only).
>
Day 2 after reboot:
Mem: 100M Active, 415M Inact, 969M Wired, 83M Cache, 199M Buf, 21M Free
Sum: 1588MB
1/4 of total RAM disappeared already.
Anyone knows what possibly happening here or maybe I should hire some
voodoo shaman to expel memory-eating-ghost from the machine ;)?
--
Bartosz Stec
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