linux-kernel - Re: [PATCH v2] VMware Balloon driver

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Date:	Wed, 21 Apr 2010 16:54:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dmitry Torokhov <dtor@...are.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>,
	Avi Kivity <avi@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH v2] VMware Balloon driver

On Thu, 15 Apr 2010 14:00:31 -0700
Dmitry Torokhov <dtor@...are.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@...are.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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