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



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)


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