Re: [CFT] delayed allocation and multipage I/O patches for 2.5.6.

[Andrew Morton]

Hanna Linder wrote:
> 
> --On Monday, March 11, 2002 22:00:57 -0800 Andrew Morton <[e-mail]> wrote:
> 
> >    "help, help - there's no point in just one guy testing this" (thanks Randy).
> 
>         Will you accept the testing of a gal? ;)

With alacrity :)  Thanks.

> >
> > This is an update of the delayed-allocation and multipage pagecache I/O
> > patches.  I'm calling this a beta, because it all works, and I have
> > other stuff to do for a while.
> >
> 
>         Here are the dbench throughput results on an 8-way SMP with 2GB memory.
> These are run with 64 then 128 clients 15 times each averaged. It looked
> pretty good.
>         Running with more than 180 clients caused the system to hang, after
> a reset there was much filesystem corruption. This happened twice. Probably
> related to filling up disk space.

It could be space-related.  A couple of gigs should have been plenty..

One other possible explanation is to do with radix-tree pagecache.
It has to allocate memory to add nodes to the tree.  When these
allocations start failing due to out-of-memory, the VM will keep
on calling swap_out() a trillion times without noticing that it
didn't work out.  But if this happened, yo would have seen a huge
number of "0-order allocation failed" messages.

> There are no ServerRaid drivers for 2.5 yet
> so the biggest disks on this system are unusable. lockmeter results are forthcoming (day or two).
> 
> Running dbench on an 8-way SMP 15 times each.
> 
> 2.5.6 clean
> 
> Clients         Avg
> 
> 64              37.9821
> 128             29.8258
> 
> 2.5.6 with everything.patch
> 
> Clients         Avg
> 
> 64              41.0204
> 128             30.6431
> 

That's odd.  I'm showing 50% increases in dbench throughput.  Not
that there's anything particularly clever about that - these patches
allow the kernel to just throw more memory in dbench's direction, and
it likes that.  But it does indicate that something funny is up.
I'll take a closer look - thanks again.

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