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[Qemu-devel] Re: [RFC] virtio: Report new guest memory statistics pertin

From: Anthony Liguori
Subject: [Qemu-devel] Re: [RFC] virtio: Report new guest memory statistics pertinent to memory ballooning
Date: Thu, 05 Nov 2009 17:36:52 -0600
User-agent: Thunderbird (X11/20090825)

address@hidden wrote:
    [RFC] virtio: Report new guest memory statistics pertinent to memory 
When using ballooning to manage overcommitted memory on a host, a system for
    guests to communicate their memory usage to the host can provide information
    that will minimize the impact of ballooning on the guests.  The current 
    employs a daemon running in each guest that communicates memory statistics 
to a
    host daemon at a specified time interval.  The host daemon aggregates this
    information and inflates and/or deflates balloons according to the level of
    host memory pressure.  This approach is effective but overly complex since a
    daemon must be installed inside each guest and coordinated to communicate 
    the host.  A simpler approach is to collect memory statistics in the virtio
    balloon driver and communicate them to the host via the device config space.
This patch implements the qemu side of the communication channel. I will post
    the kernel driver modifications in-reply to this message.
I'd like to pose a few questions concerning my implementation: * Is there a better way to use feature codes than using one per variable?

I think it's the right granularity personally.

     * This patch causes the 'info balloon' monitor command to generate output 
       the following:
(qemu) info balloon
        balloon: actual=1024 MB
        balloon: pswapin=0 pages
        balloon: pswapout=0 pages
        balloon: panon=3928 KB
        balloon: pgmajfault=0
        balloon: pgminfault=247914
        balloon: memfree=987032 KB
        balloon: memtot=1020812 KB

We could probably use less obscure names for these stats like total_memory. I know we're facing a global shortage of bits but I think this is excessive conservation :-)

We typically print these out as:

balloon: actual=1024,pswapin=0,pswapout=0,panon=3928...

It's a bit less readable admittedly, but it's how things tend to work.

Is this agreeable? Thank you for your comments... Signed-off-by: Adam Litke <address@hidden>\

The indent is pretty strange here.  git-send-email should help.

diff --git a/balloon.h b/balloon.h
index 60b4a5d..3f67021 100644
--- a/balloon.h
+++ b/balloon.h
@@ -14,14 +14,21 @@
 #ifndef _QEMU_BALLOON_H
 #define _QEMU_BALLOON_H

+#include "hw/virtio-balloon.h"
 #include "cpu-defs.h"

-typedef ram_addr_t (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
+struct QEMUBalloonState {
+    ram_addr_t actual;
+    struct virtio_balloon_stats stats;

We like to typedef the struct away from structures in qemu. See CodingStyle.

The rest looks good.


Anthony Liguori

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