Re: [Xen-users] how can empty xen disk cache??

[Radhya sahal <rad_cs_2006@xxxxxxxxx>]

--- On Mon, 7/25/11, Pasi Kärkkäinen <pasik@xxxxxx> wrote:

T hank's Pasi ,
I tried to run this command drop cache in VM and physical(dom0) before i put my question in the group !!!
echo 3 >/proc/sys/vm/drop_caches
dom0 actually empty cache but there is not any effect the files in VM still in the cache??

On Sun, Jul 24, 2011 at 08:45:49AM -0700, Radhya sahal wrote:
>    HI Pasi,
>    thanks for your cooperation,this the XML configuration VM file
>    name = "vm2"
>    uuid = "70bf5c52-91ed-fbd5-4eb7-f6acc52c3168"
>    maxmem = 2277
>    memory = 1024
>    vcpus = 1
>    bootloader = "/usr/bin/pygrub"
>    kernel = "/var/lib/xen/boot_kernel.313tN4"
>    ramdisk = "/var/lib/xen/boot_ramdisk.vV9Kd9"
>    extra = "ro root=/dev/VolGroup00/LogVol00 rhgb quiet"
>   
>   
>   
>    vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
>    disk = [ "tap:aio:/var/lib/xen/images/vm2.img,xvda,w" ]
>    vif = [
>    "mac=00:16:36:1e:3a:dc,bridge=virbr0,script=vif-bridge,vifname=vif2.0" ]
>     i am new user for xen so i think maybe you the backend in xen tap:aio ??
>    how can be sure the  VM cache is empty with out restart VM??
>

So yeah, you're using tap:aio: backend.
You shouldn't have any dom0 caching then.

Do you perhaps have a RAID controller with memory cache module?

You could try running the "drop caches" in dom0, and see if that changes anything..

-- Pasi

>
>    --- On Sun, 7/24/11, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
>
>      From: Pasi Kärkkäinen <pasik@xxxxxx>
>      Subject: Re: [Xen-users] how can empty xen disk cache??
>      To: "Radhya sahal" <rad_cs_2006@xxxxxxxxx>
>      Cc: "xen list" <xen-users@xxxxxxxxxxxxxxxxxxx>
>      Date: Sunday, July 24, 2011, 3:21 AM
>
>      On Sat, Jul 23, 2011 at 06:46:58PM -0700, Radhya sahal wrote:
>      >    thank's Mark and Pasi,
>      >    i use centos and xen ,either dom0 and vm run centos 5.5.
>      >    in the vm i run java application which it reads e.g( text file ,table
>      in
>      >    database,....).
>      >    in the first read get actual total run-time but if i try to read more
>      than
>      >    one . the file be in cache and get a very very short time ..!!!
>      >    although i try to empty the vm cache and physical(dom0) cache!!!
>      >    echo 3 >/proc/sys/vm/drop_caches
>      >    i want to read more than one to calculate the the right average
>      run-time for
>      >    the vm resource allocation and  compare this averages with other vm
>      resource
>      >    allocations ???
>      >
>
>      I repeat the question: Which disk backend are you using in dom0 for the VM
>      ?
>
>      -- Pasi
>
>      >    --- On Sat, 7/23/11, Pasi Kärkkäinen <[1]pasik@xxxxxx> wrote:
>      >
>      >      From: Pasi Kärkkäinen <[2]pasik@xxxxxx>
>      >      Subject: Re: [Xen-users] how can empty xen disk cache??
>      >      To: "Mark Pryor" <[3]tlviewer@xxxxxxxxx>
>      >      Cc: "Radhya sahal" <[4]rad_cs_2006@xxxxxxxxx>,
>      >      "[5]xen-users@xxxxxxxxxxxxxxxxxxx"
>      <[6]xen-users@xxxxxxxxxxxxxxxxxxx>
>      >      Date: Saturday, July 23, 2011, 6:44 AM
>      >
>      >      On Fri, Jul 22, 2011 at 07:11:57PM -0700, Mark Pryor wrote:
>      >      >
>      >
>      --------------------------------------------------------------------------
>      >      >
>      >      >    From: Radhya sahal <[7]rad_cs_2006@xxxxxxxxx>
>      >      >    To: [8]xen-users@xxxxxxxxxxxxxxxxxxx
>      >      >    Sent: Friday, July 22, 2011 5:36 PM
>      >      >    Subject: [Xen-users] how can empty xen disk cache??
>      >      >
>      >      >    hi
>      >      >    I am new user for xen
>      >      >    i have VM and i run java application on it ..
>      >      >    i want to empty cache for vm
>      >      >    i do that with
>      >      >    echo 3 >/proc/sys/vm/drop_caches
>      >      >    and the same command in physical machine
>      >      >    but there is not any effect
>      >      >    i think the vm have own cache in xen
>      >      >    how can empty xen disk cache??
>      >      >    thanks
>      >      >
>      >      >    check options in /etc/sysconfig/xendomains or (etc/default --
>      in
>      >      debian)
>      >      >    and turn off save/restore.
>      >      >
>      >
>      >      I don't think the question has nothing to do with save/restore.
>      >
>      >      Dom0 does not usually cache domU disk IO, unless you're using file:
>      >      backend.
>      >      Which disk backends are you using?
>      >
>      >      tap:aio and phy: backends bypass the dom0 page cache,
>      >      and thus those backends don't have any caching in xen dom0.
>      >
>      >      Xen hypervisor itself does not have cache of any kind.
>      >
>      >      -- Pasi
>
> References
>
>    Visible links
>    1. file:///mc/compose?to=pasik@xxxxxx
>    2. file:///mc/compose?to=pasik@xxxxxx
>    3. file:///mc/compose?to=tlviewer@xxxxxxxxx
>    4. file:///mc/compose?to=rad_cs_2006@xxxxxxxxx
>    5. file:///mc/compose?to=xen-users@xxxxxxxxxxxxxxxxxxx
>    6. file:///mc/compose?to=xen-users@xxxxxxxxxxxxxxxxxxx
>    7. file:///mc/compose?to=rad_cs_2006@xxxxxxxxx
>    8. file:///mc/compose?to=xen-users@xxxxxxxxxxxxxxxxxxx

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