Re: [libvirt] [Question] Is it ok to occupy large amount of cache when save?
On 02/18/2014 09:06 PM, Wangyufei (James) wrote:
Hello,
When I call virDomainManagedSave, libvirtd will fork a child process libvirt_iohelper
to write save file, and the system cache will
increase soon just like this:
Swap: 0M total, 0M used, 0M free, 1668M cached
Swap: 0M total, 0M used, 0M free, 1715M cached
Yep, that's what the kernel does if you don't use 'virsh managedsave
--bypass-cache'.
But I have cgroup to control the memory of libvirtd below 50 M, so in this case,
libvirt_iohelper will be killed, and virDomainManagedSave failed.
So my question is:
1. Is it ok for libvirtd to occupy large amount of cache when save? Can we flush
cache in time?
2. In my situation, is it any good idea to help me out? Increase the memory limit
value? Pass through the cache? Flush cache? Or any one better? Which one
do you preffer?
Try using the --bypass-cache flag (VIR_DOMAIN_SAVE_BYPASS_CACHE), which
tells libvirt to use O_DIRECT which in turn avoids filling the kernel
file system cache (won't work on tmpfs, which is why it is not default).
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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