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    SubjectRe: [PATCH v2] VMware Balloon driver
    On Thu, 15 Apr 2010 14:00:31 -0700
    Dmitry Torokhov <dtor@vmware.com> wrote:

    > This is standalone version of VMware Balloon driver. Ballooning is a
    > technique that allows hypervisor dynamically limit the amount of memory
    > available to the guest (with guest cooperation). In the overcommit
    > scenario, when hypervisor set detects that it needs to shuffle some memory,
    > it instructs the driver to allocate certain number of pages, and the
    > underlying memory gets returned to the hypervisor. Later hypervisor may
    > return memory to the guest by reattaching memory to the pageframes and
    > instructing the driver to "deflate" balloon.
    >
    > Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
    > ---
    >
    > Unlike previous version, that tried to integrate VMware ballooning transport
    > into virtio subsystem, and use stock virtio_ballon driver, this one implements
    > both controlling thread/algorithm and hypervisor transport.
    >
    > We are submitting standalone driver because KVM maintainer (Avi Kivity)
    > expressed opinion (rightly) that our transport does not fit well into
    > virtqueue paradigm and thus it does not make much sense to integrate
    > with virtio.
    >
    > There were also some concerns whether current ballooning technique is
    > the right thing. If there appears a better framework to achieve this we
    > are prepared to evaluate and switch to using it, but in the meantime
    > we'd like to get this driver upstream.
    >
    > Changes since v1:
    > - added comments throughout the code;
    > - exported stats moved from /proc to debugfs;
    > - better changelog.
    >
    >
    > ...
    >
    > +#define VMW_BALLOON_NOSLEEP_ALLOC_MAX 16384U
    > +
    > +#define VMW_BALLOON_RATE_ALLOC_MIN 512U
    > +#define VMW_BALLOON_RATE_ALLOC_MAX 2048U
    > +#define VMW_BALLOON_RATE_ALLOC_INC 16U
    > +
    > +#define VMW_BALLOON_RATE_FREE_MIN 512U
    > +#define VMW_BALLOON_RATE_FREE_MAX 16384U
    > +#define VMW_BALLOON_RATE_FREE_INC 16U

    hum. What do these do and what units are they in? Needs a comment?

    >
    > ...
    >
    > +#define VMWARE_BALLOON_CMD(cmd, data, result) \
    > +({ \
    > + unsigned long __stat, __dummy1, __dummy2; \
    > + __asm__ __volatile__ ("inl (%%dx)" : \
    > + "=a"(__stat), \
    > + "=c"(__dummy1), \
    > + "=d"(__dummy2), \
    > + "=b"(result) : \
    > + "0"(VMW_BALLOON_HV_MAGIC), \
    > + "1"(VMW_BALLOON_CMD_##cmd), \
    > + "2"(VMW_BALLOON_HV_PORT), \
    > + "3"(data) : \
    > + "memory"); \
    > + result &= -1UL; \
    > + __stat & -1UL; \
    > +})

    This is OK for both x86_32 and x86_64?

    Was it actually intended that this driver be enabled for 32-bit?

    > +#define STATS_INC(stat) (stat)++
    > +
    > +struct vmballoon_stats {
    > + unsigned int timer;
    > +
    > + /* allocation statustics */
    > + unsigned int alloc;
    > + unsigned int alloc_fail;
    > + unsigned int sleep_alloc;
    > + unsigned int sleep_alloc_fail;
    > + unsigned int refused_alloc;
    > + unsigned int refused_free;
    > + unsigned int free;
    > +
    > + /* monitor operations */
    > + unsigned int lock;
    > + unsigned int lock_fail;
    > + unsigned int unlock;
    > + unsigned int unlock_fail;
    > + unsigned int target;
    > + unsigned int target_fail;
    > + unsigned int start;
    > + unsigned int start_fail;
    > + unsigned int guest_type;
    > + unsigned int guest_type_fail;
    > +};
    > +
    > +struct vmballoon {
    > +
    > + /* list of reserved physical pages */
    > + struct list_head pages;
    > +
    > + /* transient list of non-balloonable pages */
    > + struct list_head refused_pages;
    > +
    > + /* balloon size in pages */
    > + unsigned int size;
    > + unsigned int target;
    > +
    > + /* reset flag */
    > + bool reset_required;
    > +
    > + /* adjustment rates (pages per second) */
    > + unsigned int rate_alloc;
    > + unsigned int rate_free;
    > +
    > + /* slowdown page allocations for next few cycles */
    > + unsigned int slow_allocation_cycles;
    > +
    > + /* statistics */
    > + struct vmballoon_stats stats;
    > +
    > + /* debugfs file exporting statistics */
    > + struct dentry *dbg_entry;
    > +
    > + struct sysinfo sysinfo;
    > +
    > + struct delayed_work dwork;
    > +};

    afaict all the stats stuff is useless if CONFIG_DEBUG_FS=n. Perhaps in
    that case the vmballoon.stats field should be omitted and STATS_INC
    be made a no-op?

    >
    > ...
    >



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