[RFC] makedumpfile: Improve reading speed with mmap()

[HATAYAMA Daisuke]

From: Atsushi Kumagai <kumagai-atsushi at mxc.nes.nec.co.jp>
Subject: [RFC] makedumpfile: Improve reading speed with mmap()
Date: Wed, 6 Mar 2013 15:48:04 +0900

> Hello,
> 
> I made the prototype patch to use mmap() on /proc/vmcore for
> benchmarking.
> 
> This patch simply replaces read(2) with mmap(2), I think we can see
> the pure performance improvement by reducing the number of map/unmap.
> 
>   - When /proc/vmcore supports mmap(), readmem() calls read_with_mmap() 
>     to read /proc/vmcore with mmap() instead of read().
> 
>   - Introduce --map-size <Kbyte> option to specify the map size.
>     This option is necessary to use mmap() in this patch, but just for
>     benchmarking. I'll remove this option in release version and change
>     the map size into suitable constant size to get enough performance
>     improvement.
> 
>   - This patch is based on devel branch:
>     http://makedumpfile.git.sourceforge.net/git/gitweb.cgi?p=makedumpfile/makedumpfile;a=shortlog;h=refs/heads/devel
> 
> Unfortunately, I haven't done test and benchmarking in 2nd kernel yet
> because I can't start up newer kernel as 2nd kernel on my machine.
> (It seems just my environment issue.) 
> 
> At least, this patch works for vmcores saved on local disk,
> so it will work in 2nd kernel too.
> 
> If anyone helps to do benchmarking, it's very helpful for me.
> And any comments for this patch are welcome.

Kumagai-san,

I think it necessary to compare this generic one with the idea
considering virtual memory mapping, which should affect filtering
performance to some degree.

http://lists.infradead.org/pipermail/kexec/2013-February/007982.html

I guess implementation can relatively be moduler. I'll post a
prorotype patch for benchmark later.

Thanks.
HATAYAMA, Daisuke