Does Cyrus benefit greatly from increased FS buffer cache?

[Andrew Morgan]

On Thu, 16 Apr 2009, Sebastian Hagedorn wrote:

> --On 16. April 2009 10:58:15 +1000 Rob Mueller <robm at fastmail.fm> wrote:
>
>>> http://blog.fastmail.fm/2007/09/21/reiserfs-bugs-32-bit-vs-64-bit-kernel
>>> s-cache-vs-inode-memory/
>>> 
>>> Anyone have any specific thoughts?  Is there any other benefit we might
>>> see from large memory allocation in 64-bit architecture?
>> 
>> Given that I wrote that blog post, I can only tell you that in our
>> environment, 64-bit kernels made a big difference.
>
> I wonder if ext3 behaves differently, Red Hat's 32-bit behaves differently, 
> or if something altogether different is going on. We are currently running 
> RHEL 3 in 32-bit mode, our servers have 16 GB, and most of it is used for 
> caching:
>
> # free
>            total       used       free     shared    buffers     cached
> Mem:      16214344   16197612      16732          0      86944   13415172
> -/+ buffers/cache:    2695496   13518848
> Swap:      4192944       8436    4184508
>
> So it would seem that a 64-bit kernel wouldn't improve on that, right? Or is 
> that a difference between 2.4 and 2.6?

That's interesting, and not what I expected.  :)  What does "cat 
/proc/meminfo" show?  My 64-bit kernel running cyrus has:

MemTotal:      4051576 kB
MemFree:         31452 kB
Buffers:        478716 kB
Cached:        2471240 kB
SwapCached:          0 kB
Active:        1562596 kB
Inactive:      1768236 kB
SwapTotal:     2000052 kB
SwapFree:      1999396 kB
Dirty:            1484 kB
Writeback:          40 kB
AnonPages:      380888 kB
Mapped:          68340 kB
Slab:           601940 kB
SReclaimable:   500604 kB
SUnreclaim:     101336 kB
PageTables:      41220 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   4025840 kB
Committed_AS:   659524 kB
VmallocTotal: 34359738367 kB
VmallocUsed:    280476 kB
VmallocChunk: 34359457535 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     2048 kB

On an older system running a 32-bit "686" kernel, it shows:

MemTotal:      2076312 kB
MemFree:         73008 kB
Buffers:         61916 kB
Cached:        1512400 kB
SwapCached:          0 kB
Active:         429292 kB
Inactive:      1467944 kB
HighTotal:     1179392 kB
HighFree:         8400 kB
LowTotal:       896920 kB
LowFree:         64608 kB
SwapTotal:     2000052 kB
SwapFree:      1999988 kB
Dirty:             140 kB
Writeback:           0 kB
AnonPages:      322960 kB
Mapped:          24180 kB
Slab:            77336 kB
SReclaimable:    45836 kB
SUnreclaim:      31500 kB
PageTables:       5900 kB
NFS_Unstable:       12 kB
Bounce:              0 kB
CommitLimit:   3038208 kB
Committed_AS:   598964 kB
VmallocTotal:   114680 kB
VmallocUsed:      3936 kB
VmallocChunk:   110188 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     4096 kB


Note the HighTotal, HighFree, LowTotal, and LowFree lines that are not 
present in a 64-bit kernel.

 	Andy