Re: [PATCH v15 4/5] mm: support reporting free page blocks

2017-08-28 Thread Wei Wang 

On 08/28/2017 09:33 PM, Michal Hocko wrote:

On Mon 28-08-17 18:08:32, Wei Wang wrote:

This patch adds support to walk through the free page blocks in the
system and report them via a callback function. Some page blocks may
leave the free list after zone->lock is released, so it is the caller's
responsibility to either detect or prevent the use of such pages.

One use example of this patch is to accelerate live migration by skipping
the transfer of free pages reported from the guest. A popular method used
by the hypervisor to track which part of memory is written during live
migration is to write-protect all the guest memory. So, those pages that
are reported as free pages but are written after the report function
returns will be captured by the hypervisor, and they will be added to the
next round of memory transfer.

OK, looks much better. I still have few nits.


+extern void walk_free_mem_block(void *opaque,
+   int min_order,
+   bool (*report_page_block)(void *, unsigned long,
+ unsigned long));
+

please add names to arguments of the prototype


  /*
   * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
   * into the buddy system. The freed pages will be poisoned with pattern
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d00f74..81eedc7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4762,6 +4762,71 @@ void show_free_areas(unsigned int filter, nodemask_t 
*nodemask)
show_swap_cache_info();
  }
  
+/**

+ * walk_free_mem_block - Walk through the free page blocks in the system
+ * @opaque: the context passed from the caller
+ * @min_order: the minimum order of free lists to check
+ * @report_page_block: the callback function to report free page blocks

page_block has meaning in the core MM which doesn't strictly match its
usage here. Moreover we are reporting pfn ranges rather than struct page
range. So report_pfn_range would suit better.

[...]

+   for_each_populated_zone(zone) {
+   for (order = MAX_ORDER - 1; order >= min_order; order--) {
+   for (mt = 0; !stop && mt < MIGRATE_TYPES; mt++) {
+   spin_lock_irqsave(>lock, flags);
+   list = >free_area[order].free_list[mt];
+   list_for_each_entry(page, list, lru) {
+   pfn = page_to_pfn(page);
+   stop = report_page_block(opaque, pfn,
+1 << order);
+   if (stop)
+   break;

if (stop) {

spin_unlock_irqrestore(>lock, flags);
return;
}

would be both easier and less error prone. E.g. You wouldn't pointlessly
iterate over remaining orders just to realize there is nothing to be
done for those...



Yes, that's better, thanks. I will take other suggestions as well.

Best,
Wei



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Re: [PATCH v15 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

2017-08-28 Thread Wei Wang 

On 08/29/2017 02:03 AM, Michael S. Tsirkin wrote:

On Mon, Aug 28, 2017 at 06:08:31PM +0800, Wei Wang wrote:

Add a new feature, VIRTIO_BALLOON_F_SG, which enables the transfer
of balloon (i.e. inflated/deflated) pages using scatter-gather lists
to the host.

The implementation of the previous virtio-balloon is not very
efficient, because the balloon pages are transferred to the
host one by one. Here is the breakdown of the time in percentage
spent on each step of the balloon inflating process (inflating
7GB of an 8GB idle guest).

1) allocating pages (6.5%)
2) sending PFNs to host (68.3%)
3) address translation (6.1%)
4) madvise (19%)

It takes about 4126ms for the inflating process to complete.
The above profiling shows that the bottlenecks are stage 2)
and stage 4).

This patch optimizes step 2) by transferring pages to the host in
sgs. An sg describes a chunk of guest physically continuous pages.
With this mechanism, step 4) can also be optimized by doing address
translation and madvise() in chunks rather than page by page.

With this new feature, the above ballooning process takes ~597ms
resulting in an improvement of ~86%.

TODO: optimize stage 1) by allocating/freeing a chunk of pages
instead of a single page each time.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
Suggested-by: Michael S. Tsirkin 
---
  drivers/virtio/virtio_balloon.c | 171 
  include/uapi/linux/virtio_balloon.h |   1 +
  2 files changed, 155 insertions(+), 17 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index f0b3a0b..8ecc1d4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -32,6 +32,8 @@
  #include 
  #include 
  #include 
+#include 
+#include 
  
  /*

   * Balloon device works in 4K page units.  So each page is pointed to by
@@ -79,6 +81,9 @@ struct virtio_balloon {
/* Synchronize access/update to this struct virtio_balloon elements */
struct mutex balloon_lock;
  
+	/* The xbitmap used to record balloon pages */

+   struct xb page_xb;
+
/* The array of pfns we tell the Host about. */
unsigned int num_pfns;
__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
@@ -141,13 +146,111 @@ static void set_page_pfns(struct virtio_balloon *vb,
  page_to_balloon_pfn(page) + i);
  }
  
+static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size)

+{
+   struct scatterlist sg;
+
+   sg_init_one(, addr, size);
+   return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
+}
+
+static void send_balloon_page_sg(struct virtio_balloon *vb,
+struct virtqueue *vq,
+void *addr,
+uint32_t size,
+bool batch)
+{
+   unsigned int len;
+   int err;
+
+   err = add_one_sg(vq, addr, size);
+   /* Sanity check: this can't really happen */
+   WARN_ON(err);

It might be cleaner to detect that add failed due to
ring full and kick then. Just an idea, up to you
whether to do it.


+
+   /* If batching is in use, we batch the sgs till the vq is full. */
+   if (!batch || !vq->num_free) {
+   virtqueue_kick(vq);
+   wait_event(vb->acked, virtqueue_get_buf(vq, ));
+   /* Release all the entries if there are */

Meaning
Account for all used entries if any
?


+   while (virtqueue_get_buf(vq, ))
+   ;


Above code is reused below. Add a function?


+   }
+}
+
+/*
+ * Send balloon pages in sgs to host. The balloon pages are recorded in the
+ * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
+ * The page xbitmap is searched for continuous "1" bits, which correspond
+ * to continuous pages, to chunk into sgs.
+ *
+ * @page_xb_start and @page_xb_end form the range of bits in the xbitmap that
+ * need to be searched.
+ */
+static void tell_host_sgs(struct virtio_balloon *vb,
+ struct virtqueue *vq,
+ unsigned long page_xb_start,
+ unsigned long page_xb_end)
+{
+   unsigned long sg_pfn_start, sg_pfn_end;
+   void *sg_addr;
+   uint32_t sg_len, sg_max_len = round_down(UINT_MAX, PAGE_SIZE);
+
+   sg_pfn_start = page_xb_start;
+   while (sg_pfn_start < page_xb_end) {
+   sg_pfn_start = xb_find_next_bit(>page_xb, sg_pfn_start,
+   page_xb_end, 1);
+   if (sg_pfn_start == page_xb_end + 1)
+   break;
+   sg_pfn_end = xb_find_next_bit(>page_xb, sg_pfn_start + 1,
+ page_xb_end, 0);
+   sg_addr = (void *)pfn_to_kaddr(sg_pfn_start);
+   sg_len = (sg_pfn_end - sg_pfn_start) <<

Re: [PATCH v15 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

2017-08-28 Thread Michael S. Tsirkin 
On Mon, Aug 28, 2017 at 06:08:31PM +0800, Wei Wang wrote:
> Add a new feature, VIRTIO_BALLOON_F_SG, which enables the transfer
> of balloon (i.e. inflated/deflated) pages using scatter-gather lists
> to the host.
> 
> The implementation of the previous virtio-balloon is not very
> efficient, because the balloon pages are transferred to the
> host one by one. Here is the breakdown of the time in percentage
> spent on each step of the balloon inflating process (inflating
> 7GB of an 8GB idle guest).
> 
> 1) allocating pages (6.5%)
> 2) sending PFNs to host (68.3%)
> 3) address translation (6.1%)
> 4) madvise (19%)
> 
> It takes about 4126ms for the inflating process to complete.
> The above profiling shows that the bottlenecks are stage 2)
> and stage 4).
> 
> This patch optimizes step 2) by transferring pages to the host in
> sgs. An sg describes a chunk of guest physically continuous pages.
> With this mechanism, step 4) can also be optimized by doing address
> translation and madvise() in chunks rather than page by page.
> 
> With this new feature, the above ballooning process takes ~597ms
> resulting in an improvement of ~86%.
> 
> TODO: optimize stage 1) by allocating/freeing a chunk of pages
> instead of a single page each time.
> 
> Signed-off-by: Wei Wang 
> Signed-off-by: Liang Li 
> Suggested-by: Michael S. Tsirkin 
> ---
>  drivers/virtio/virtio_balloon.c | 171 
> 
>  include/uapi/linux/virtio_balloon.h |   1 +
>  2 files changed, 155 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index f0b3a0b..8ecc1d4 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -32,6 +32,8 @@
>  #include 
>  #include 
>  #include 
> +#include 
> +#include 
>  
>  /*
>   * Balloon device works in 4K page units.  So each page is pointed to by
> @@ -79,6 +81,9 @@ struct virtio_balloon {
>   /* Synchronize access/update to this struct virtio_balloon elements */
>   struct mutex balloon_lock;
>  
> + /* The xbitmap used to record balloon pages */
> + struct xb page_xb;
> +
>   /* The array of pfns we tell the Host about. */
>   unsigned int num_pfns;
>   __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
> @@ -141,13 +146,111 @@ static void set_page_pfns(struct virtio_balloon *vb,
> page_to_balloon_pfn(page) + i);
>  }
>  
> +static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size)
> +{
> + struct scatterlist sg;
> +
> + sg_init_one(, addr, size);
> + return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
> +}
> +
> +static void send_balloon_page_sg(struct virtio_balloon *vb,
> +  struct virtqueue *vq,
> +  void *addr,
> +  uint32_t size,
> +  bool batch)
> +{
> + unsigned int len;
> + int err;
> +
> + err = add_one_sg(vq, addr, size);
> + /* Sanity check: this can't really happen */
> + WARN_ON(err);

It might be cleaner to detect that add failed due to
ring full and kick then. Just an idea, up to you
whether to do it.

> +
> + /* If batching is in use, we batch the sgs till the vq is full. */
> + if (!batch || !vq->num_free) {
> + virtqueue_kick(vq);
> + wait_event(vb->acked, virtqueue_get_buf(vq, ));
> + /* Release all the entries if there are */

Meaning
Account for all used entries if any
?

> + while (virtqueue_get_buf(vq, ))
> + ;


Above code is reused below. Add a function?

> + }
> +}
> +
> +/*
> + * Send balloon pages in sgs to host. The balloon pages are recorded in the
> + * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
> + * The page xbitmap is searched for continuous "1" bits, which correspond
> + * to continuous pages, to chunk into sgs.
> + *
> + * @page_xb_start and @page_xb_end form the range of bits in the xbitmap that
> + * need to be searched.
> + */
> +static void tell_host_sgs(struct virtio_balloon *vb,
> +   struct virtqueue *vq,
> +   unsigned long page_xb_start,
> +   unsigned long page_xb_end)
> +{
> + unsigned long sg_pfn_start, sg_pfn_end;
> + void *sg_addr;
> + uint32_t sg_len, sg_max_len = round_down(UINT_MAX, PAGE_SIZE);
> +
> + sg_pfn_start = page_xb_start;
> + while (sg_pfn_start < page_xb_end) {
> + sg_pfn_start = xb_find_next_bit(>page_xb, sg_pfn_start,
> + page_xb_end, 1);
> + if (sg_pfn_start == page_xb_end + 1)
> + break;
> + sg_pfn_end = xb_find_next_bit(>page_xb, sg_pfn_start + 1,
> +   page_xb_end, 0);
> + sg_addr =

Re: [PATCH v15 4/5] mm: support reporting free page blocks

2017-08-28 Thread Michal Hocko 
On Mon 28-08-17 15:33:26, Michal Hocko wrote:
> On Mon 28-08-17 18:08:32, Wei Wang wrote:
> > This patch adds support to walk through the free page blocks in the
> > system and report them via a callback function. Some page blocks may
> > leave the free list after zone->lock is released, so it is the caller's
> > responsibility to either detect or prevent the use of such pages.
> > 
> > One use example of this patch is to accelerate live migration by skipping
> > the transfer of free pages reported from the guest. A popular method used
> > by the hypervisor to track which part of memory is written during live
> > migration is to write-protect all the guest memory. So, those pages that
> > are reported as free pages but are written after the report function
> > returns will be captured by the hypervisor, and they will be added to the
> > next round of memory transfer.
> 
> OK, looks much better. I still have few nits.
> 
> > +extern void walk_free_mem_block(void *opaque,
> > +   int min_order,
> > +   bool (*report_page_block)(void *, unsigned long,
> > + unsigned long));
> > +
> 
> please add names to arguments of the prototype

And one more thing. Your callback returns bool and true usually means a
success while you are using it to break out from the loop. This is
rather confusing. I would expect iterating until false is returned so
the opposite than what you have. You could also change this to int and
return 0 on success and < 0 to break out. 

-- 
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SUSE Labs
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Re: [PATCH v15 4/5] mm: support reporting free page blocks

2017-08-28 Thread Michal Hocko 
On Mon 28-08-17 18:08:32, Wei Wang wrote:
> This patch adds support to walk through the free page blocks in the
> system and report them via a callback function. Some page blocks may
> leave the free list after zone->lock is released, so it is the caller's
> responsibility to either detect or prevent the use of such pages.
> 
> One use example of this patch is to accelerate live migration by skipping
> the transfer of free pages reported from the guest. A popular method used
> by the hypervisor to track which part of memory is written during live
> migration is to write-protect all the guest memory. So, those pages that
> are reported as free pages but are written after the report function
> returns will be captured by the hypervisor, and they will be added to the
> next round of memory transfer.

OK, looks much better. I still have few nits.

> +extern void walk_free_mem_block(void *opaque,
> + int min_order,
> + bool (*report_page_block)(void *, unsigned long,
> +   unsigned long));
> +

please add names to arguments of the prototype

>  /*
>   * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
>   * into the buddy system. The freed pages will be poisoned with pattern
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6d00f74..81eedc7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4762,6 +4762,71 @@ void show_free_areas(unsigned int filter, nodemask_t 
> *nodemask)
>   show_swap_cache_info();
>  }
>  
> +/**
> + * walk_free_mem_block - Walk through the free page blocks in the system
> + * @opaque: the context passed from the caller
> + * @min_order: the minimum order of free lists to check
> + * @report_page_block: the callback function to report free page blocks

page_block has meaning in the core MM which doesn't strictly match its
usage here. Moreover we are reporting pfn ranges rather than struct page
range. So report_pfn_range would suit better.

[...]
> + for_each_populated_zone(zone) {
> + for (order = MAX_ORDER - 1; order >= min_order; order--) {
> + for (mt = 0; !stop && mt < MIGRATE_TYPES; mt++) {
> + spin_lock_irqsave(>lock, flags);
> + list = >free_area[order].free_list[mt];
> + list_for_each_entry(page, list, lru) {
> + pfn = page_to_pfn(page);
> + stop = report_page_block(opaque, pfn,
> +  1 << order);
> + if (stop)
> + break;

if (stop) {

spin_unlock_irqrestore(>lock, flags);
return;
}

would be both easier and less error prone. E.g. You wouldn't pointlessly
iterate over remaining orders just to realize there is nothing to be
done for those...

> + }
> + spin_unlock_irqrestore(>lock, flags);
> + }
> + }
> + }
> +}
> +EXPORT_SYMBOL_GPL(walk_free_mem_block);

-- 
Michal Hocko
SUSE Labs
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[PATCH v15 5/5] virtio-balloon: VIRTIO_BALLOON_F_CTRL_VQ

2017-08-28 Thread Wei Wang 
Add a new vq, ctrl_vq, to handle commands between the host and guest.
With this feature, we will be able to have the control plane and data
plane separated. In other words, the control related data of each
feature will be sent via the ctrl_vq cmds, meanwhile each feature may
have its own data plane vq.

Free page report is the the first new feature controlled via ctrl_vq,
and a new cmd class, VIRTIO_BALLOON_CTRLQ_CLASS_FREE_PAGE, is added.
Currently, this feature has two cmds:
VIRTIO_BALLOON_FREE_PAGE_F_START: This cmd is sent from host to guest
to start the free page reporting work.
VIRTIO_BALLOON_FREE_PAGE_F_STOP: This cmd is used bidirectionally. The
guest would send the cmd to the host to indicate the reporting work is
done. The host would send the cmd to the guest to actively request the
stop of the reporting work.

The free_page_vq is used to transmit the guest free page blocks to the
host.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
---
 drivers/virtio/virtio_balloon.c | 247 +---
 include/uapi/linux/virtio_balloon.h |  15 +++
 2 files changed, 242 insertions(+), 20 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 8ecc1d4..1d384a4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -55,7 +55,13 @@ static struct vfsmount *balloon_mnt;
 
 struct virtio_balloon {
struct virtio_device *vdev;
-   struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
+   struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *ctrl_vq,
+*free_page_vq;
+
+   /* Balloon's own wq for cpu-intensive work items */
+   struct workqueue_struct *balloon_wq;
+   /* The work items submitted to the balloon wq are listed here */
+   struct work_struct report_free_page_work;
 
/* The balloon servicing is delegated to a freezable workqueue. */
struct work_struct update_balloon_stats_work;
@@ -65,6 +71,9 @@ struct virtio_balloon {
spinlock_t stop_update_lock;
bool stop_update;
 
+   /* Stop reporting free pages */
+   bool report_free_page_stop;
+
/* Waiting for host to ack the pages we released. */
wait_queue_head_t acked;
 
@@ -93,6 +102,11 @@ struct virtio_balloon {
 
/* To register callback in oom notifier call chain */
struct notifier_block nb;
+
+   /* Host to guest ctrlq cmd buf for free page report */
+   struct virtio_balloon_ctrlq_cmd free_page_cmd_in;
+   /* Guest to Host ctrlq cmd buf for free page report */
+   struct virtio_balloon_ctrlq_cmd free_page_cmd_out;
 };
 
 static struct virtio_device_id id_table[] = {
@@ -177,6 +191,26 @@ static void send_balloon_page_sg(struct virtio_balloon *vb,
}
 }
 
+static void send_free_page_sg(struct virtqueue *vq, void *addr, uint32_t size)
+{
+   unsigned int len;
+   int err = -ENOSPC;
+
+   do {
+   if (vq->num_free) {
+   err = add_one_sg(vq, addr, size);
+   /* Sanity check: this can't really happen */
+   WARN_ON(err);
+   if (!err)
+   virtqueue_kick(vq);
+   }
+
+   /* Release entries if there are */
+   while (virtqueue_get_buf(vq, ))
+   ;
+   } while (err == -ENOSPC && vq->num_free);
+}
+
 /*
  * Send balloon pages in sgs to host. The balloon pages are recorded in the
  * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
@@ -525,42 +559,206 @@ static void update_balloon_size_func(struct work_struct 
*work)
queue_work(system_freezable_wq, work);
 }
 
-static int init_vqs(struct virtio_balloon *vb)
+static bool virtio_balloon_send_free_pages(void *opaque, unsigned long pfn,
+  unsigned long nr_pages)
+{
+   struct virtio_balloon *vb = (struct virtio_balloon *)opaque;
+   void *addr = (void *)pfn_to_kaddr(pfn);
+   uint32_t len = nr_pages << PAGE_SHIFT;
+
+   if (vb->report_free_page_stop)
+   return 1;
+
+   send_free_page_sg(vb->free_page_vq, addr, len);
+
+   return 0;
+}
+
+static void ctrlq_add_cmd(struct virtqueue *vq,
+ struct virtio_balloon_ctrlq_cmd *cmd,
+ bool inbuf)
 {
-   struct virtqueue *vqs[3];
-   vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request 
};
-   static const char * const names[] = { "inflate", "deflate", "stats" };
-   int err, nvqs;
+   struct scatterlist sg;
+   int err;
+
+   sg_init_one(, cmd, sizeof(struct virtio_balloon_ctrlq_cmd));
+   if (inbuf)
+   err = virtqueue_add_inbuf(vq, , 1, cmd, GFP_KERNEL);
+   else
+   err = virtqueue_add_outbuf(vq, , 1, cmd, GFP_KERNEL);
+
+   /* Sanity check: this can't

[PATCH v15 4/5] mm: support reporting free page blocks

2017-08-28 Thread Wei Wang 
This patch adds support to walk through the free page blocks in the
system and report them via a callback function. Some page blocks may
leave the free list after zone->lock is released, so it is the caller's
responsibility to either detect or prevent the use of such pages.

One use example of this patch is to accelerate live migration by skipping
the transfer of free pages reported from the guest. A popular method used
by the hypervisor to track which part of memory is written during live
migration is to write-protect all the guest memory. So, those pages that
are reported as free pages but are written after the report function
returns will be captured by the hypervisor, and they will be added to the
next round of memory transfer.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
Cc: Michal Hocko 
Cc: Michael S. Tsirkin 
---
 include/linux/mm.h |  5 +
 mm/page_alloc.c| 65 ++
 2 files changed, 70 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 46b9ac5..3c4267d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1835,6 +1835,11 @@ extern void free_area_init_node(int nid, unsigned long * 
zones_size,
unsigned long zone_start_pfn, unsigned long *zholes_size);
 extern void free_initmem(void);
 
+extern void walk_free_mem_block(void *opaque,
+   int min_order,
+   bool (*report_page_block)(void *, unsigned long,
+ unsigned long));
+
 /*
  * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
  * into the buddy system. The freed pages will be poisoned with pattern
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d00f74..81eedc7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4762,6 +4762,71 @@ void show_free_areas(unsigned int filter, nodemask_t 
*nodemask)
show_swap_cache_info();
 }
 
+/**
+ * walk_free_mem_block - Walk through the free page blocks in the system
+ * @opaque: the context passed from the caller
+ * @min_order: the minimum order of free lists to check
+ * @report_page_block: the callback function to report free page blocks
+ *
+ * If the callback returns 1, stop iterating the list of free page blocks.
+ * Otherwise, continue to report.
+ *
+ * Please note that there are no locking guarantees for the callback and
+ * that the reported pfn range might be freed or disappear after the
+ * callback returns so the caller has to be very careful how it is used.
+ *
+ * The callback itself must not sleep or perform any operations which would
+ * require any memory allocations directly (not even GFP_NOWAIT/GFP_ATOMIC)
+ * or via any lock dependency. It is generally advisable to implement
+ * the callback as simple as possible and defer any heavy lifting to a
+ * different context.
+ *
+ * There is no guarantee that each free range will be reported only once
+ * during one walk_free_mem_block invocation.
+ *
+ * pfn_to_page on the given range is strongly discouraged and if there is
+ * an absolute need for that make sure to contact MM people to discuss
+ * potential problems.
+ *
+ * The function itself might sleep so it cannot be called from atomic
+ * contexts.
+ *
+ * In general low orders tend to be very volatile and so it makes more
+ * sense to query larger ones first for various optimizations which like
+ * ballooning etc... This will reduce the overhead as well.
+ */
+void walk_free_mem_block(void *opaque,
+int min_order,
+bool (*report_page_block)(void *, unsigned long,
+  unsigned long))
+{
+   struct zone *zone;
+   struct page *page;
+   struct list_head *list;
+   int order;
+   enum migratetype mt;
+   unsigned long pfn, flags;
+   bool stop = 0;
+
+   for_each_populated_zone(zone) {
+   for (order = MAX_ORDER - 1; order >= min_order; order--) {
+   for (mt = 0; !stop && mt < MIGRATE_TYPES; mt++) {
+   spin_lock_irqsave(>lock, flags);
+   list = >free_area[order].free_list[mt];
+   list_for_each_entry(page, list, lru) {
+   pfn = page_to_pfn(page);
+   stop = report_page_block(opaque, pfn,
+1 << order);
+   if (stop)
+   break;
+   }
+   spin_unlock_irqrestore(>lock, flags);
+   }
+   }
+   }
+}
+EXPORT_SYMBOL_GPL(walk_free_mem_block);
+
 static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
 {

[PATCH v15 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

2017-08-28 Thread Wei Wang 
Add a new feature, VIRTIO_BALLOON_F_SG, which enables the transfer
of balloon (i.e. inflated/deflated) pages using scatter-gather lists
to the host.

The implementation of the previous virtio-balloon is not very
efficient, because the balloon pages are transferred to the
host one by one. Here is the breakdown of the time in percentage
spent on each step of the balloon inflating process (inflating
7GB of an 8GB idle guest).

1) allocating pages (6.5%)
2) sending PFNs to host (68.3%)
3) address translation (6.1%)
4) madvise (19%)

It takes about 4126ms for the inflating process to complete.
The above profiling shows that the bottlenecks are stage 2)
and stage 4).

This patch optimizes step 2) by transferring pages to the host in
sgs. An sg describes a chunk of guest physically continuous pages.
With this mechanism, step 4) can also be optimized by doing address
translation and madvise() in chunks rather than page by page.

With this new feature, the above ballooning process takes ~597ms
resulting in an improvement of ~86%.

TODO: optimize stage 1) by allocating/freeing a chunk of pages
instead of a single page each time.

Signed-off-by: Wei Wang 
Signed-off-by: Liang Li 
Suggested-by: Michael S. Tsirkin 
---
 drivers/virtio/virtio_balloon.c | 171 
 include/uapi/linux/virtio_balloon.h |   1 +
 2 files changed, 155 insertions(+), 17 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index f0b3a0b..8ecc1d4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -32,6 +32,8 @@
 #include 
 #include 
 #include 
+#include 
+#include 
 
 /*
  * Balloon device works in 4K page units.  So each page is pointed to by
@@ -79,6 +81,9 @@ struct virtio_balloon {
/* Synchronize access/update to this struct virtio_balloon elements */
struct mutex balloon_lock;
 
+   /* The xbitmap used to record balloon pages */
+   struct xb page_xb;
+
/* The array of pfns we tell the Host about. */
unsigned int num_pfns;
__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
@@ -141,13 +146,111 @@ static void set_page_pfns(struct virtio_balloon *vb,
  page_to_balloon_pfn(page) + i);
 }
 
+static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size)
+{
+   struct scatterlist sg;
+
+   sg_init_one(, addr, size);
+   return virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
+}
+
+static void send_balloon_page_sg(struct virtio_balloon *vb,
+struct virtqueue *vq,
+void *addr,
+uint32_t size,
+bool batch)
+{
+   unsigned int len;
+   int err;
+
+   err = add_one_sg(vq, addr, size);
+   /* Sanity check: this can't really happen */
+   WARN_ON(err);
+
+   /* If batching is in use, we batch the sgs till the vq is full. */
+   if (!batch || !vq->num_free) {
+   virtqueue_kick(vq);
+   wait_event(vb->acked, virtqueue_get_buf(vq, ));
+   /* Release all the entries if there are */
+   while (virtqueue_get_buf(vq, ))
+   ;
+   }
+}
+
+/*
+ * Send balloon pages in sgs to host. The balloon pages are recorded in the
+ * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE.
+ * The page xbitmap is searched for continuous "1" bits, which correspond
+ * to continuous pages, to chunk into sgs.
+ *
+ * @page_xb_start and @page_xb_end form the range of bits in the xbitmap that
+ * need to be searched.
+ */
+static void tell_host_sgs(struct virtio_balloon *vb,
+ struct virtqueue *vq,
+ unsigned long page_xb_start,
+ unsigned long page_xb_end)
+{
+   unsigned long sg_pfn_start, sg_pfn_end;
+   void *sg_addr;
+   uint32_t sg_len, sg_max_len = round_down(UINT_MAX, PAGE_SIZE);
+
+   sg_pfn_start = page_xb_start;
+   while (sg_pfn_start < page_xb_end) {
+   sg_pfn_start = xb_find_next_bit(>page_xb, sg_pfn_start,
+   page_xb_end, 1);
+   if (sg_pfn_start == page_xb_end + 1)
+   break;
+   sg_pfn_end = xb_find_next_bit(>page_xb, sg_pfn_start + 1,
+ page_xb_end, 0);
+   sg_addr = (void *)pfn_to_kaddr(sg_pfn_start);
+   sg_len = (sg_pfn_end - sg_pfn_start) << PAGE_SHIFT;
+   while (sg_len > sg_max_len) {
+   send_balloon_page_sg(vb, vq, sg_addr, sg_max_len, 1);
+   sg_addr += sg_max_len;
+   sg_len -= sg_max_len;
+   }
+   send_balloon_page_sg(vb, vq, sg_addr, sg_len, 1);
+   xb_zero(>page_xb,

[PATCH v15 2/5] lib/xbitmap: add xb_find_next_bit() and xb_zero()

2017-08-28 Thread Wei Wang 
xb_find_next_bit() is used to find the next "1" or "0" bit in the
given range. xb_zero() is used to zero the given range of bits.

Signed-off-by: Wei Wang 
Cc: Andrew Morton 
Cc: Matthew Wilcox 
Cc: Michal Hocko 
Cc: Michael S. Tsirkin 
---
 include/linux/xbitmap.h |  3 +++
 lib/xbitmap.c   | 39 +++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/xbitmap.h b/include/linux/xbitmap.h
index 25b05ff..0061f7a 100644
--- a/include/linux/xbitmap.h
+++ b/include/linux/xbitmap.h
@@ -38,6 +38,9 @@ static inline void xb_init(struct xb *xb)
 int xb_set_bit(struct xb *xb, unsigned long bit);
 bool xb_test_bit(struct xb *xb, unsigned long bit);
 void xb_clear_bit(struct xb *xb, unsigned long bit);
+void xb_zero(struct xb *xb, unsigned long start, unsigned long end);
+unsigned long xb_find_next_bit(struct xb *xb, unsigned long start,
+  unsigned long end, bool set);
 
 /* Check if the xb tree is empty */
 static inline bool xb_is_empty(const struct xb *xb)
diff --git a/lib/xbitmap.c b/lib/xbitmap.c
index 8c55296..b9e2a0c 100644
--- a/lib/xbitmap.c
+++ b/lib/xbitmap.c
@@ -174,3 +174,42 @@ void xb_preload(gfp_t gfp)
}
 }
 EXPORT_SYMBOL(xb_preload);
+
+/**
+ *  xb_zero - zero a range of bits in the xbitmap
+ *  @xb: the xbitmap that the bits reside in
+ *  @start: the start of the range, inclusive
+ *  @end: the end of the range, inclusive
+ */
+void xb_zero(struct xb *xb, unsigned long start, unsigned long end)
+{
+   unsigned long i;
+
+   for (i = start; i <= end; i++)
+   xb_clear_bit(xb, i);
+}
+EXPORT_SYMBOL(xb_zero);
+
+/**
+ * xb_find_next_bit - find next 1 or 0 in the give range of bits
+ * @xb: the xbitmap that the bits reside in
+ * @start: the start of the range, inclusive
+ * @end: the end of the range, inclusive
+ * @set: the polarity (1 or 0) of the next bit to find
+ *
+ * Return the index of the found bit in the xbitmap. If the returned index
+ * exceeds @end, it indicates that no such bit is found in the given range.
+ */
+unsigned long xb_find_next_bit(struct xb *xb, unsigned long start,
+  unsigned long end, bool set)
+{
+   unsigned long i;
+
+   for (i = start; i <= end; i++) {
+   if (xb_test_bit(xb, i) == set)
+   break;
+   }
+
+   return i;
+}
+EXPORT_SYMBOL(xb_find_next_bit);
-- 
2.7.4

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[PATCH v15 1/5] lib/xbitmap: Introduce xbitmap

2017-08-28 Thread Wei Wang 
From: Matthew Wilcox 

The eXtensible Bitmap is a sparse bitmap representation which is
efficient for set bits which tend to cluster.  It supports up to
'unsigned long' worth of bits, and this commit adds the bare bones --
xb_set_bit(), xb_clear_bit() and xb_test_bit().

Signed-off-by: Matthew Wilcox 
Signed-off-by: Wei Wang 
Cc: Andrew Morton 
Cc: Michal Hocko 
Cc: Michael S. Tsirkin 
---
 include/linux/radix-tree.h |   3 +
 include/linux/xbitmap.h|  61 
 lib/Makefile   |   2 +-
 lib/radix-tree.c   |  22 +-
 lib/xbitmap.c  | 176 +
 5 files changed, 260 insertions(+), 4 deletions(-)
 create mode 100644 include/linux/xbitmap.h
 create mode 100644 lib/xbitmap.c

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 3e57350..e1203b1 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -309,6 +309,8 @@ void radix_tree_iter_replace(struct radix_tree_root *,
const struct radix_tree_iter *, void __rcu **slot, void *entry);
 void radix_tree_replace_slot(struct radix_tree_root *,
 void __rcu **slot, void *entry);
+bool __radix_tree_delete(struct radix_tree_root *root,
+struct radix_tree_node *node, void __rcu **slot);
 void __radix_tree_delete_node(struct radix_tree_root *,
  struct radix_tree_node *,
  radix_tree_update_node_t update_node,
@@ -325,6 +327,7 @@ unsigned int radix_tree_gang_lookup(const struct 
radix_tree_root *,
 unsigned int radix_tree_gang_lookup_slot(const struct radix_tree_root *,
void __rcu ***results, unsigned long *indices,
unsigned long first_index, unsigned int max_items);
+int __radix_tree_preload(gfp_t gfp_mask, unsigned int nr);
 int radix_tree_preload(gfp_t gfp_mask);
 int radix_tree_maybe_preload(gfp_t gfp_mask);
 int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order);
diff --git a/include/linux/xbitmap.h b/include/linux/xbitmap.h
new file mode 100644
index 000..25b05ff
--- /dev/null
+++ b/include/linux/xbitmap.h
@@ -0,0 +1,61 @@
+/*
+ * eXtensible Bitmaps
+ * Copyright (c) 2017 Microsoft Corporation 
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * eXtensible Bitmaps provide an unlimited-size sparse bitmap facility.
+ * All bits are initially zero.
+ */
+
+#ifndef __XBITMAP_H__
+#define __XBITMAP_H__
+
+#include 
+
+struct xb {
+   struct radix_tree_root xbrt;
+};
+
+#define XB_INIT {  \
+   .xbrt = RADIX_TREE_INIT(IDR_RT_MARKER | GFP_NOWAIT),\
+}
+#define DEFINE_XB(name)struct xb name = XB_INIT
+
+static inline void xb_init(struct xb *xb)
+{
+   INIT_RADIX_TREE(>xbrt, IDR_RT_MARKER | GFP_NOWAIT);
+}
+
+int xb_set_bit(struct xb *xb, unsigned long bit);
+bool xb_test_bit(struct xb *xb, unsigned long bit);
+void xb_clear_bit(struct xb *xb, unsigned long bit);
+
+/* Check if the xb tree is empty */
+static inline bool xb_is_empty(const struct xb *xb)
+{
+   return radix_tree_empty(>xbrt);
+}
+
+void xb_preload(gfp_t gfp);
+
+/**
+ * xb_preload_end - end preload section started with xb_preload()
+ *
+ * Each xb_preload() should be matched with an invocation of this
+ * function. See xb_preload() for details.
+ */
+static inline void xb_preload_end(void)
+{
+   preempt_enable();
+}
+
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 40c1837..ea50496 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -18,7 +18,7 @@ KCOV_INSTRUMENT_dynamic_debug.o := n
 
 lib-y := ctype.o string.o vsprintf.o cmdline.o \
 rbtree.o radix-tree.o dump_stack.o timerqueue.o\
-idr.o int_sqrt.o extable.o \
+idr.o xbitmap.o int_sqrt.o extable.o \
 sha1.o chacha20.o irq_regs.o argv_split.o \
 flex_proportions.o ratelimit.o show_mem.o \
 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 898e879..ee72e2c 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -463,7 +463,7 @@ radix_tree_node_free(struct radix_tree_node *node)
  * To make use of this facility, the radix tree must be initialised without
  * __GFP_DIRECT_RECLAIM being passed to INIT_RADIX_TREE().
  */

[PATCH v15 0/5] Virtio-balloon Enhancement

2017-08-28 Thread Wei Wang 
This patch series enhances the existing virtio-balloon with the following
new features:
1) fast ballooning: transfer ballooned pages between the guest and host in
chunks using sgs, instead of one by one; and
2) free page block reporting: a new virtqueue to report guest free pages
to the host.

The second feature can be used to accelerate live migration of VMs. Here
are some details:

Live migration needs to transfer the VM's memory from the source machine
to the destination round by round. For the 1st round, all the VM's memory
is transferred. From the 2nd round, only the pieces of memory that were
written by the guest (after the 1st round) are transferred. One method
that is popularly used by the hypervisor to track which part of memory is
written is to write-protect all the guest memory.

The second feature  enables the optimization of the 1st round memory
transfer - the hypervisor can skip the transfer of guest free pages in the
1st round. It is not concerned that the memory pages are used after they
are given to the hypervisor as a hint of the free pages, because they will
be tracked by the hypervisor and transferred in the next round if they are
used and written.

Change Log:
v14->v15:
1) mm: make the report callback return a bool value - returning 1 to stop
walking through the free page list.
2) virtio-balloon: batching sgs of balloon pages till the vq is full
3) virtio-balloon: create a new workqueue, rather than using the default
system_wq, to queue the free page reporting work item.
4) virtio-balloon: add a ctrl_vq to be a central control plane which will
handle all the future control related commands between the host and guest.
Add free page report as the first feature controlled under ctrl_vq, and
the free_page_vq is a data plane vq dedicated to the transmission of free
page blocks.

v13->v14:
1) xbitmap: move the code from lib/radix-tree.c to lib/xbitmap.c.
2) xbitmap: consolidate the implementation of xb_bit_set/clear/test into
one xb_bit_ops.
3) xbitmap: add documents for the exported APIs.
4) mm: rewrite the function to walk through free page blocks.
5) virtio-balloon: when reporting a free page blcok to the device, if the
vq is full (less likey to happen in practice), just skip reporting this
block, instead of busywaiting till an entry gets released.
6) virtio-balloon: fail the probe function if adding the signal buf in
init_vqs fails.

v12->v13:
1) mm: use a callback function to handle the the free page blocks from the
report function. This avoids exposing the zone internal to a kernel
module.
2) virtio-balloon: send balloon pages or a free page block using a single
sg each time. This has the benefits of simpler implementation with no new
APIs.
3) virtio-balloon: the free_page_vq is used to report free pages only (no
multiple usages interleaving)
4) virtio-balloon: Balloon pages and free page blocks are sent via input
sgs, and the completion signal to the host is sent via an output sg.

v11->v12:
1) xbitmap: use the xbitmap from Matthew Wilcox to record ballooned pages.
2) virtio-ring: enable the driver to build up a desc chain using vring
desc.
3) virtio-ring: Add locking to the existing START_USE() and END_USE()
macro to lock/unlock the vq when a vq operation starts/ends.
4) virtio-ring: add virtqueue_kick_sync() and virtqueue_kick_async()
5) virtio-balloon: describe chunks of ballooned pages and free pages
blocks directly using one or more chains of desc from the vq.

v10->v11:
1) virtio_balloon: use vring_desc to describe a chunk;
2) virtio_ring: support to add an indirect desc table to virtqueue;
3)  virtio_balloon: use cmdq to report guest memory statistics.

v9->v10:
1) mm: put report_unused_page_block() under CONFIG_VIRTIO_BALLOON;
2) virtio-balloon: add virtballoon_validate();
3) virtio-balloon: msg format change;
4) virtio-balloon: move miscq handling to a task on system_freezable_wq;
5) virtio-balloon: code cleanup.

v8->v9:
1) Split the two new features, VIRTIO_BALLOON_F_BALLOON_CHUNKS and
VIRTIO_BALLOON_F_MISC_VQ, which were mixed together in the previous
implementation;
2) Simpler function to get the free page block.

v7->v8:
1) Use only one chunk format, instead of two.
2) re-write the virtio-balloon implementation patch.
3) commit changes
4) patch re-org


Matthew Wilcox (1):
  lib/xbitmap: Introduce xbitmap

Wei Wang (4):
  lib/xbitmap: add xb_find_next_bit() and xb_zero()
  virtio-balloon: VIRTIO_BALLOON_F_SG
  mm: support reporting free page blocks
  virtio-balloon: VIRTIO_BALLOON_F_CTRL_VQ

 drivers/virtio/virtio_balloon.c | 418 
 include/linux/mm.h  |   5 +
 include/linux/radix-tree.h  |   3 +
 include/linux/xbitmap.h |  64 ++
 include/uapi/linux/virtio_balloon.h |  16 ++
 lib/Makefile|   2 +-
 lib/radix-tree.c|  22 +-
 lib/xbitmap.c   | 215 +++
 mm/page_alloc.c |  65 ++
 9 files

RE: [RFC] virtio-iommu version 0.4

2017-08-28 Thread Tian, Kevin 
> From: Jean-Philippe Brucker [mailto:jean-philippe.bruc...@arm.com]
> Sent: Wednesday, August 23, 2017 6:01 PM
> 
> On 04/08/17 19:19, Jean-Philippe Brucker wrote:
> > Other extensions are in preparation. I won't detail them here because
> v0.4
> > already is a lot to digest, but in short, building on top of PROBE:
> >
> > * First, since the IOMMU is paravirtualized, the device can expose some
> >   properties of the physical topology to the guest, and let it allocate
> >   resources more efficiently. For example, when the virtio-iommu
> manages
> >   both physical and emulated endpoints, with different underlying
> IOMMUs,
> >   we now have a way to describe multiple page and block granularities,
> >   instead of forcing the guest to use the most restricted one for all
> >   endpoints. This will most likely be in v0.5.
> 
> In order to extend requests with PASIDs and (later) nested mode, I intend
> to rename "address_space" field to "domain", since it is a lot more
> precise about what the field is referring to and the current name would
> make these extensions confusing. Please find the rationale at [1].
> "ioasid_bits" will be "domain_bits" and "VIRTIO_IOMMU_F_IOASID_BITS"
> will
> be "VIRTIO_IOMMU_F_DOMAIN_BITS".
> 
> For those that had time to read this version, do you have other comments
> and suggestions about v0.4? Otherwise it is the only update I have for
> v0.5 (along with fine-grained address range and page size properties from
> the quoted text) and I will send it soon.
> 
> In particular, please tell me now if you see the need for other
> destructive changes like this one. They will be impossible to introduce
> once a driver or device is upstream.
> 
> Thanks,
> Jean
> 
> [1] https://www.spinics.net/lists/kvm/msg154573.html

Here comes some comments:

1.1 Motivation

You describe I/O page faults handling as future work. Seems you considered
only recoverable fault (since "aka. PCI PRI" being used). What about other
unrecoverable faults e.g. what to do if a virtual DMA request doesn't find 
a valid mapping? Even when there is no PRI support, we need some basic
form of fault reporting mechanism to indicate such errors to guest.

2.6.8.2 Property RESV_MEM

I'm not immediately clear when VIRTIO_IOMMU_PROBE_RESV_MEM_T_ABORT
should be explicitly reported. Is there any real example on bare metal IOMMU?
usually reserved memory is reported to CPU through other method (e.g. e820
on x86 platform). Of course MSI is a special case which is covered by BYPASS 
and MSI flag... If yes, maybe you can also include an example in implementation 
notes.

Another thing I want to ask your opinion, about whether there is value of
adding another subtype (MEM_T_IDENTITY), asking for identity mapping
in the address space. It's similar to Reserved Memory Region Reporting
(RMRR) structure defined in VT-d, to indicate BIOS allocated reserved
memory ranges which may be DMA target and has to be identity mapped
when DMA remapping is enabled. I'm not sure whether ARM has similar
capability and whether there might be a general usage beyond VT-d. For
now the only usage in my mind is to assign a device with RMRR associated
on VT-d (Intel GPU, or some USB controllers) where the RMRR info needs
propagated to the guest (since identity mapping also means reservation
of virtual address space).

2.6.8.2.3 Device Requirements: Property RESV_MEM

--citation start--
If an endpoint is attached to an address space, the device SHOULD leave 
any access targeting one of its VIRTIO_IOMMU_PROBE_RESV_MEM_T_BYPASS 
regions pass through untranslated. In other words, the device SHOULD 
handle such a region as if it was identity-mapped (virtual address equal to
physical address). If the endpoint is not attached to any address space, 
then the device MAY abort the transaction.
--citation end

I have a question for the last sentence. From definition of BYPASS, it's
orthogonal to whether there is an address space attached, then should
we still allow "May abort" behavior? 

Thanks
Kevin 
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