slightly [OT] highmem (was Re: 2.4.20 at kernel.org and data logging)

[Manuel Krause <manuel.krause@mb.tu-ilmenau.de>]

On 01/18/2003 04:57 PM, Chris Mason wrote:
> On Sat, 2003-01-18 at 05:25, Russell Coker wrote:
> 
>>On Fri, 17 Jan 2003 00:51, Sewell, Cassandra D (Cassandra) wrote:
>>
>>>Is the data logging patch for 2.4.20 kernel considered
>>>complete?  I see a patch at
>>>ftp.suse.com/pub/people/mason/patches/data-logging/2.4.20.  Also will this
>>>patch be considered working for the last stable 2.4.20 posted at the
>>>kernel.org location?
>>>
>>>I am in the process of upgrading some machines from 2.2.x (I know way
>>>overdue), and need the data-logging capability.
>>
>>I am using those patches on some 2.4.20 machines running as Qmail mail 
>>servers.  I have the /var file system mounted with data journalling.
>>
>>I have 4 machines running each with >250,000 mail boxes with continual heavy 
>>IO load (the load never goes below 100 disk writes per second).
>>
>>I found the benefit to be much smaller than I had hoped.  The patches in 
>>question have a number of other performance improvements which made a huge 
>>and noticable difference.  data=journal seemed to make a small difference, 
>>but nothing exciting.
> 
> 
> The benefit from data=journal varies largely by the size of the files in
> use.  But Russell, you might be hitting other bottlenecks having to do
> with reading the directory items off disk (that many directories means
> lots of inode).  
> 
> Also, we should probably try switching you to a highmem io enabled
> kernel, I'm almost done with a patch to put the 2.4.21 data logging code
> in the -aa kernel.
> 

Some OT(?) things to ask:

* Does enabled highmem support make any sense for mem<1G ?
* I especially wondered about the advantages of processors'
   "pae" feature in this context.
* VMware WS (I depend on) unfortunately doesn't support
   systems with enabled "pae" :-((

For the moment I only found out that highmem 64G didn't bring so to say 
"subjectively" measurable advantages on here (mem=512M) and -- VMware 
wouldn't run...

Thanks in advance,

Manuel