[CFT] ZFS v15 patch (version 3)

[Martin Matuska]

 Without head-12636.patch you are unable to reproduce the deadlock?

Dňa 14. 7. 2010 2:14, Peter Jeremy  wrote / napísal(a):
> On 2010-Jul-08 23:30:33 +0200, Martin Matuska <mm at FreeBSD.org> wrote:
>> On 8. 7. 2010 22:04, Peter Jeremy  wrote / napísal(a):
>>> Without patching arc_memory_throttle(), a system behaves especially
>>> poorly if it uses ZFS with any of mmap(2), UFS or NFS client - in my
>>> case, ports/mail/mairix was almost guaranteed to wedge the system.
>>> This is the problem that the following hack is intended to work around:
>>>   perl -e '$x = "x" x 1000000;'
>>>
>>>   
>> Regarding ARC, you might want to try the revision 209227 from head that
>> is scheduled for MFC on 18.7.2010:
>> http://people.freebsd.org/~mm/patches/zfs/head-12636.patch
> I have done some testing with 8-STABLE with head-12636.patch and have
> managed to successfully reproduce a deadlock.  The system is amd64
> with 2GB RAM running a mixed UFS+ZFS environment.  On a freshly booted
> system, I unmount/remount my ZFS /home and a UFS scratch filesystem
> that contains a 1.5GB file [ensuring there is no cached data from
> either FS].  I then dd(1) the 1.5GB UFS file to /dev/null and, once
> that is finished, start mairix on my ~6GB mail directory (on ZFS
> /home).  After some time, I get the following 'systat -v' output:
>
>     4 users    Load  9.30  8.97  8.33                  Jul 14 09:49
>
> Mem:KB    REAL            VIRTUAL                       VN PAGER   SWAP PAGER
>         Tot   Share      Tot    Share    Free           in   out     in   out
> Act  122308    4436   721892     7876   59824  count      
> All  418376    7020 1074594k    38920          pages      
> Proc:                                                            Interrupts
>   r   p   d   s   w   Csw  Trp  Sys  Int  Sof  Flt        cow    4031 total
>   4          76      133k    3  194   30  135             zfod        ata0 irq14
>                                                           ozfod    30 bge0 irq16
> 99.8%Sys   0.2%Intr  0.0%User  0.0%Nice  0.0%Idle        %ozfod       atapci1 20
> |    |    |    |    |    |    |    |    |    |    |       daefr       uhci0 ehci
> ==================================================        prcfr       uhci1 22
>                                            dtbuf          totfr  2000 cpu0: time
> Namei     Name-cache   Dir-cache    100000 desvn          react  2001 cpu1: time
>    Calls    hits   %    hits   %       918 numvn          pdwak
>                                        273 frevn          pdpgs
>                                                           intrn
> Disks   ad0   ad1                                  540404 wire
> KB/t   0.00  0.00                                  297512 act
> tps       0     0                                 1122808 inact
> MB/s   0.00  0.00                                   57876 cache
> %busy     0     0                                    1948 free
>                                                    218192 buf
>
> Apart from normal daemons, the only processes running are vmstat,
> systat and mairix (via SSH sessions).  Note that the system is running
> at virtually 100%sys with extremely low free memory and extremely high
> context switches but no obviously useful activity.  At this stage, the
> system is basically unusable (I can't even kill the mairix process).
>
> My understanding of the problem is that the VM system sees "available"
> RAM as the sum of "cache" and "free" - which is reasonably high so
> there is no pressure to free up "inact" RAM.  OTOH, ZFS ARC only
> counts "free" RAM - which is critically low so it throttles itself
> but has no way to get the VM system to move RAM onto the "free" list.
>