[libvirt] [PATCH] init: raise default system aio limits

[Laine Stump]

On 10/04/2011 12:59 PM, Eric Blake wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=740899 documents that
> if qemu uses aio=native for its disks, then it consumes 128 aio
> requests per disk.  On a host with multiple guests, this can quickly
> run out of kernel aio requests with the default aio-max-nr of
> 65536.  Kernel developers have confirmed that there is no up-front
> cost to raising this limit (a larger limit merely implies that more
> aio requests can be issued in parallel, which in turn will result
> in more kernel memory allocation if the system really does use that
> many requests).  Since the system default limit prevents 256 disks,
> which is well within libvirt's current scalability, this patch
> installs a file to raise the limit and document it in case a system
> administrator has further cause to tune the limit.  The install
> only works on platforms new enough to source /etc/sysctl.d/*
> alongside /etc/sysctl.conf (F14 and RHEL 6).

ACK. This all makes sense and seems fairly thoroughly researched. (Would 
be good to actually try it, though)