top shows only part of available physmem

Bartosz Stec bartosz.stec at it4pro.pl
Thu Jan 27 13:56:35 UTC 2011


W dniu 2011-01-27 04:21, Jeremy Chadwick pisze:
> On Thu, Jan 27, 2011 at 01:59:01AM +0100, Bartosz Stec wrote:
>> W dniu 2011-01-26 19:44, John Baldwin pisze:
>>> On Wednesday, January 26, 2011 1:04:02 pm Marco van Tol wrote:
>>>> On Wed, Jan 26, 2011 at 12:35:56PM -0500, John Baldwin wrote:
>>>>> On Wednesday, January 26, 2011 8:20:28 am Bartosz Stec wrote:
>>>>>> W dniu 2011-01-26 14:06, John Baldwin pisze:
>>>>>>> On Wednesday, January 26, 2011 7:20:34 am Bartosz Stec wrote:
>>>>>>>> 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).

-- 
Bartosz Stec




More information about the freebsd-stable mailing list