[PATCH v24 1/2] mm: support reporting free page blocks
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
Acked-by: Michal Hocko
---
include/linux/mm.h | 6
mm/page_alloc.c| 91 ++
2 files changed, 97 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ea818ff..b3077dd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
+unsigned long pfn,
+unsigned long num));
+
/*
* 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 76c9688..705de22 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter, nodemask_t
*nodemask)
show_swap_cache_info();
}
+/*
+ * Walk through a free page list and report the found pfn range via the
+ * callback.
+ *
+ * Return false if the callback requests to stop reporting. Otherwise,
+ * return true.
+ */
+static bool walk_free_page_list(void *opaque,
+ struct zone *zone,
+ int order,
+ enum migratetype mt,
+ bool (*report_pfn_range)(void *,
+unsigned long,
+unsigned long))
+{
+ struct page *page;
+ struct list_head *list;
+ unsigned long pfn, flags;
+ bool ret;
+
+ spin_lock_irqsave(&zone->lock, flags);
+ list = &zone->free_area[order].free_list[mt];
+ list_for_each_entry(page, list, lru) {
+ pfn = page_to_pfn(page);
+ ret = report_pfn_range(opaque, pfn, 1 << order);
+ if (!ret)
+ break;
+ }
+ spin_unlock_irqrestore(&zone->lock, flags);
+
+ return ret;
+}
+
+/**
+ * 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_pfn_range: the callback to report the pfn range of the free pages
+ *
+ * If the callback returns false, 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_pfn_range)(void *opaque,
+ unsigned long pfn,
+ unsigned long num))
+{
+ s
Re: [PATCH v24 1/2] mm: support reporting free page blocks
On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
>
> Signed-off-by: Wei Wang
> Signed-off-by: Liang Li
> Cc: Michal Hocko
> Cc: Michael S. Tsirkin
> Acked-by: Michal Hocko
> ---
> include/linux/mm.h | 6
> mm/page_alloc.c| 91
> ++
> 2 files changed, 97 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ea818ff..b3077dd 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> + unsigned long pfn,
> + unsigned long num));
> +
> /*
> * 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 76c9688..705de22 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter, nodemask_t
> *nodemask)
> show_swap_cache_info();
> }
>
> +/*
> + * Walk through a free page list and report the found pfn range via the
> + * callback.
> + *
> + * Return false if the callback requests to stop reporting. Otherwise,
> + * return true.
> + */
> +static bool walk_free_page_list(void *opaque,
> + struct zone *zone,
> + int order,
> + enum migratetype mt,
> + bool (*report_pfn_range)(void *,
> + unsigned long,
> + unsigned long))
> +{
> + struct page *page;
> + struct list_head *list;
> + unsigned long pfn, flags;
> + bool ret;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> + list = &zone->free_area[order].free_list[mt];
> + list_for_each_entry(page, list, lru) {
> + pfn = page_to_pfn(page);
> + ret = report_pfn_range(opaque, pfn, 1 << order);
> + if (!ret)
> + break;
> + }
> + spin_unlock_irqrestore(&zone->lock, flags);
> +
> + return ret;
> +}
There are two issues with this API. One is that it is not
restarteable: if you return false, you start from the
beginning. So no way to drop lock, do something slow
and then proceed.
Another is that you are using it to report free page hints. Presumably
the point is to drop these pages - keeping them near head of the list
and reusing the reported ones will just make everything slower
invalidating the hint.
How about rotating these pages towards the end of the list?
Probably not on each call, callect reported pages and then
move them to tail when we exit.
Of course it's possible not all reporters want this.
So maybe change the callback to return int:
0 - page reported, move page to end of free list
> 0 - page skipped, proceed
< 0 - stop processing
> +
> +/**
> + * 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_pfn_range: the callback to report the pfn range of the free pages
> + *
> + * If the callback returns false, 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
Re: [PATCH v24 1/2] mm: support reporting free page blocks
>
> On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
> >
> > Signed-off-by: Wei Wang
> > Signed-off-by: Liang Li
> > Cc: Michal Hocko
> > Cc: Michael S. Tsirkin
> > Acked-by: Michal Hocko
> > ---
> > include/linux/mm.h | 6
> > mm/page_alloc.c| 91
> > ++
> > 2 files changed, 97 insertions(+)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ea818ff..b3077dd 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> > +unsigned long pfn,
> > +unsigned long num));
> > +
> > /*
> > * 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 76c9688..705de22 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter, nodemask_t
> > *nodemask)
> > show_swap_cache_info();
> > }
> >
> > +/*
> > + * Walk through a free page list and report the found pfn range via the
> > + * callback.
> > + *
> > + * Return false if the callback requests to stop reporting. Otherwise,
> > + * return true.
> > + */
> > +static bool walk_free_page_list(void *opaque,
> > + struct zone *zone,
> > + int order,
> > + enum migratetype mt,
> > + bool (*report_pfn_range)(void *,
> > +unsigned long,
> > +unsigned long))
> > +{
> > + struct page *page;
> > + struct list_head *list;
> > + unsigned long pfn, flags;
> > + bool ret;
> > +
> > + spin_lock_irqsave(&zone->lock, flags);
> > + list = &zone->free_area[order].free_list[mt];
> > + list_for_each_entry(page, list, lru) {
> > + pfn = page_to_pfn(page);
> > + ret = report_pfn_range(opaque, pfn, 1 << order);
> > + if (!ret)
> > + break;
> > + }
> > + spin_unlock_irqrestore(&zone->lock, flags);
> > +
> > + return ret;
> > +}
>
> There are two issues with this API. One is that it is not
> restarteable: if you return false, you start from the
> beginning. So no way to drop lock, do something slow
> and then proceed.
>
> Another is that you are using it to report free page hints. Presumably
> the point is to drop these pages - keeping them near head of the list
> and reusing the reported ones will just make everything slower
> invalidating the hint.
I think that's where patches[1] by 'Nitesh' will help: This patch-set
will send free page hints transparently to host and host decides to delete such
pages.
If I compare with patchset by 'Wei', host gets/asks free page hints and ignore
such pages during live migration. But as already discussed, if free pages are
still in guest memory there is no point of traversing & getting all such pages
again.
[1] https://www.spinics.net/lists/kvm/msg159790.html
>
> How about rotating these pages towards the end of the list?
> Probably not on each call, callect reported pages and then
> move them to tail when we exit.
>
> Of course it's possible not all reporters want this.
> So maybe change the callback to return int:
> 0 - page reported, move page to end of free list
> > 0 - page skipped, proceed
> < 0 - stop processing
>
>
> > +
> > +/**
> > + * 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_pfn_range: the callback to report the pfn rang
Re: [PATCH v24 1/2] mm: support reporting free page blocks
On Thu, Jan 25, 2018 at 09:56:01AM -0500, Pankaj Gupta wrote:
>
> >
> > On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
> > >
> > > Signed-off-by: Wei Wang
> > > Signed-off-by: Liang Li
> > > Cc: Michal Hocko
> > > Cc: Michael S. Tsirkin
> > > Acked-by: Michal Hocko
> > > ---
> > > include/linux/mm.h | 6
> > > mm/page_alloc.c| 91
> > > ++
> > > 2 files changed, 97 insertions(+)
> > >
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index ea818ff..b3077dd 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> > > + unsigned long pfn,
> > > + unsigned long num));
> > > +
> > > /*
> > > * 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 76c9688..705de22 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter,
> > > nodemask_t
> > > *nodemask)
> > > show_swap_cache_info();
> > > }
> > >
> > > +/*
> > > + * Walk through a free page list and report the found pfn range via the
> > > + * callback.
> > > + *
> > > + * Return false if the callback requests to stop reporting. Otherwise,
> > > + * return true.
> > > + */
> > > +static bool walk_free_page_list(void *opaque,
> > > + struct zone *zone,
> > > + int order,
> > > + enum migratetype mt,
> > > + bool (*report_pfn_range)(void *,
> > > + unsigned long,
> > > + unsigned long))
> > > +{
> > > + struct page *page;
> > > + struct list_head *list;
> > > + unsigned long pfn, flags;
> > > + bool ret;
> > > +
> > > + spin_lock_irqsave(&zone->lock, flags);
> > > + list = &zone->free_area[order].free_list[mt];
> > > + list_for_each_entry(page, list, lru) {
> > > + pfn = page_to_pfn(page);
> > > + ret = report_pfn_range(opaque, pfn, 1 << order);
> > > + if (!ret)
> > > + break;
> > > + }
> > > + spin_unlock_irqrestore(&zone->lock, flags);
> > > +
> > > + return ret;
> > > +}
> >
> > There are two issues with this API. One is that it is not
> > restarteable: if you return false, you start from the
> > beginning. So no way to drop lock, do something slow
> > and then proceed.
> >
> > Another is that you are using it to report free page hints. Presumably
> > the point is to drop these pages - keeping them near head of the list
> > and reusing the reported ones will just make everything slower
> > invalidating the hint.
>
> I think that's where patches[1] by 'Nitesh' will help: This patch-set
> will send free page hints transparently to host and host decides to delete
> such
> pages.
>
> If I compare with patchset by 'Wei', host gets/asks free page hints and
> ignore
> such pages during live migration. But as already discussed, if free pages are
> still in guest memory there is no point of traversing & getting all such pages
> again.
>
> [1] https://www.spinics.net/lists/kvm/msg159790.html
The main difference between Wei's and Nitesh's patches add hints to page
alloc/free path. It's this more risky performance-wise: you need to
enable it at guest boot, not just at migration time.
Maybe the overhead isn't big, unfortunately no one posted any
numbers yet.
--
MST
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Virtualization mailing list
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Re: [PATCH v24 1/2] mm: support reporting free page blocks
On 01/25/2018 09:41 PM, Michael S. Tsirkin wrote:
On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
Signed-off-by: Wei Wang
Signed-off-by: Liang Li
Cc: Michal Hocko
Cc: Michael S. Tsirkin
Acked-by: Michal Hocko
---
include/linux/mm.h | 6
mm/page_alloc.c| 91 ++
2 files changed, 97 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ea818ff..b3077dd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
+unsigned long pfn,
+unsigned long num));
+
/*
* 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 76c9688..705de22 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter, nodemask_t
*nodemask)
show_swap_cache_info();
}
+/*
+ * Walk through a free page list and report the found pfn range via the
+ * callback.
+ *
+ * Return false if the callback requests to stop reporting. Otherwise,
+ * return true.
+ */
+static bool walk_free_page_list(void *opaque,
+ struct zone *zone,
+ int order,
+ enum migratetype mt,
+ bool (*report_pfn_range)(void *,
+unsigned long,
+unsigned long))
+{
+ struct page *page;
+ struct list_head *list;
+ unsigned long pfn, flags;
+ bool ret;
+
+ spin_lock_irqsave(&zone->lock, flags);
+ list = &zone->free_area[order].free_list[mt];
+ list_for_each_entry(page, list, lru) {
+ pfn = page_to_pfn(page);
+ ret = report_pfn_range(opaque, pfn, 1 << order);
+ if (!ret)
+ break;
+ }
+ spin_unlock_irqrestore(&zone->lock, flags);
+
+ return ret;
+}
There are two issues with this API. One is that it is not
restarteable: if you return false, you start from the
beginning. So no way to drop lock, do something slow
and then proceed.
Another is that you are using it to report free page hints. Presumably
the point is to drop these pages - keeping them near head of the list
and reusing the reported ones will just make everything slower
invalidating the hint.
How about rotating these pages towards the end of the list?
Probably not on each call, callect reported pages and then
move them to tail when we exit.
I'm not sure how this would help. For example, we have a list of 2M free
page blocks:
A-->B-->C-->D-->E-->F-->G--H
After reporting A and B, and put them to the end and exit, when the
caller comes back,
1) if the list remains unchanged, then it will be
C-->D-->E-->F-->G-->H-->A-->B
2) If worse, all the blocks have been split into smaller blocks and used
after the caller comes back.
where could we continue?
The reason to think about "restart" is the worry about the virtqueue is
full, right? But we've agreed that losing some hints to report isn't
important, and in practice, the virtqueue won't be full as the host side
is faster.
I'm concerned that actions on the free list may cause more controversy
though it might be safe to do from some aspect, and would be hard to end
debating. If possible, we could go with the most prudent approach for
now, and have more discussions in future improvement patches. What would
you think?
+
+/**
+ * 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
Re: [PATCH v24 1/2] mm: support reporting free page blocks
On Fri, Jan 26, 2018 at 11:29:15AM +0800, Wei Wang wrote:
> On 01/25/2018 09:41 PM, Michael S. Tsirkin wrote:
> > On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
> > >
> > > Signed-off-by: Wei Wang
> > > Signed-off-by: Liang Li
> > > Cc: Michal Hocko
> > > Cc: Michael S. Tsirkin
> > > Acked-by: Michal Hocko
> > > ---
> > > include/linux/mm.h | 6
> > > mm/page_alloc.c| 91
> > > ++
> > > 2 files changed, 97 insertions(+)
> > >
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index ea818ff..b3077dd 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> > > + unsigned long pfn,
> > > + unsigned long num));
> > > +
> > > /*
> > >* 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 76c9688..705de22 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter,
> > > nodemask_t *nodemask)
> > > show_swap_cache_info();
> > > }
> > > +/*
> > > + * Walk through a free page list and report the found pfn range via the
> > > + * callback.
> > > + *
> > > + * Return false if the callback requests to stop reporting. Otherwise,
> > > + * return true.
> > > + */
> > > +static bool walk_free_page_list(void *opaque,
> > > + struct zone *zone,
> > > + int order,
> > > + enum migratetype mt,
> > > + bool (*report_pfn_range)(void *,
> > > + unsigned long,
> > > + unsigned long))
> > > +{
> > > + struct page *page;
> > > + struct list_head *list;
> > > + unsigned long pfn, flags;
> > > + bool ret;
> > > +
> > > + spin_lock_irqsave(&zone->lock, flags);
> > > + list = &zone->free_area[order].free_list[mt];
> > > + list_for_each_entry(page, list, lru) {
> > > + pfn = page_to_pfn(page);
> > > + ret = report_pfn_range(opaque, pfn, 1 << order);
> > > + if (!ret)
> > > + break;
> > > + }
> > > + spin_unlock_irqrestore(&zone->lock, flags);
> > > +
> > > + return ret;
> > > +}
> > There are two issues with this API. One is that it is not
> > restarteable: if you return false, you start from the
> > beginning. So no way to drop lock, do something slow
> > and then proceed.
> >
> > Another is that you are using it to report free page hints. Presumably
> > the point is to drop these pages - keeping them near head of the list
> > and reusing the reported ones will just make everything slower
> > invalidating the hint.
> >
> > How about rotating these pages towards the end of the list?
> > Probably not on each call, callect reported pages and then
> > move them to tail when we exit.
>
>
> I'm not sure how this would help. For example, we have a list of 2M free
> page blocks:
> A-->B-->C-->D-->E-->F-->G--H
>
> After reporting A and B, and put them to the end and exit, when the caller
> comes back,
> 1) if the list remains unchanged, then it will be
> C-->D-->E-->F-->G-->H-->A-->B
Right. So here we can just scan until we see A, right? It's a harder
question what to do if A and only A has been consumed. We don't want B
to be sent twice ideally. OTOH maybe that isn't a big deal if it's only
twice. Host might know page is already gone - how about host gives us a
hint after using the buffer?
> 2) If worse, all the blocks have been split into smaller blo
Re: [PATCH v24 1/2] mm: support reporting free page blocks
On Fri, Jan 26, 2018 at 05:00:09PM +0200, Michael S. Tsirkin wrote:
> On Fri, Jan 26, 2018 at 11:29:15AM +0800, Wei Wang wrote:
> > On 01/25/2018 09:41 PM, Michael S. Tsirkin wrote:
> > > On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
> > > >
> > > > Signed-off-by: Wei Wang
> > > > Signed-off-by: Liang Li
> > > > Cc: Michal Hocko
> > > > Cc: Michael S. Tsirkin
> > > > Acked-by: Michal Hocko
> > > > ---
> > > > include/linux/mm.h | 6
> > > > mm/page_alloc.c| 91
> > > > ++
> > > > 2 files changed, 97 insertions(+)
> > > >
> > > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > > index ea818ff..b3077dd 100644
> > > > --- a/include/linux/mm.h
> > > > +++ b/include/linux/mm.h
> > > > @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> > > > +unsigned long
> > > > pfn,
> > > > +unsigned long
> > > > num));
> > > > +
> > > > /*
> > > >* 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 76c9688..705de22 100644
> > > > --- a/mm/page_alloc.c
> > > > +++ b/mm/page_alloc.c
> > > > @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter,
> > > > nodemask_t *nodemask)
> > > > show_swap_cache_info();
> > > > }
> > > > +/*
> > > > + * Walk through a free page list and report the found pfn range via the
> > > > + * callback.
> > > > + *
> > > > + * Return false if the callback requests to stop reporting. Otherwise,
> > > > + * return true.
> > > > + */
> > > > +static bool walk_free_page_list(void *opaque,
> > > > + struct zone *zone,
> > > > + int order,
> > > > + enum migratetype mt,
> > > > + bool (*report_pfn_range)(void *,
> > > > +unsigned long,
> > > > +unsigned long))
> > > > +{
> > > > + struct page *page;
> > > > + struct list_head *list;
> > > > + unsigned long pfn, flags;
> > > > + bool ret;
> > > > +
> > > > + spin_lock_irqsave(&zone->lock, flags);
> > > > + list = &zone->free_area[order].free_list[mt];
> > > > + list_for_each_entry(page, list, lru) {
> > > > + pfn = page_to_pfn(page);
> > > > + ret = report_pfn_range(opaque, pfn, 1 << order);
> > > > + if (!ret)
> > > > + break;
> > > > + }
> > > > + spin_unlock_irqrestore(&zone->lock, flags);
> > > > +
> > > > + return ret;
> > > > +}
> > > There are two issues with this API. One is that it is not
> > > restarteable: if you return false, you start from the
> > > beginning. So no way to drop lock, do something slow
> > > and then proceed.
> > >
> > > Another is that you are using it to report free page hints. Presumably
> > > the point is to drop these pages - keeping them near head of the list
> > > and reusing the reported ones will just make everything slower
> > > invalidating the hint.
> > >
> > > How about rotating these pages towards the end of the list?
> > > Probably not on each call, callect reported pages and then
> > > move them to tail when we exit.
> >
> >
> > I'm not sure how this would help. For example, we have a list of 2M free
> > page blocks:
> > A-->B-->C-->D-->E-->F-->G--H
> >
> > After reporting A and B, and put them to the end and exit, when the cal
RE: [PATCH v24 1/2] mm: support reporting free page blocks
On Saturday, January 27, 2018 5:44 AM, Michael S. Tsirkin wrote: > On Fri, Jan 26, 2018 at 05:00:09PM +0200, Michael S. Tsirkin wrote: > > On Fri, Jan 26, 2018 at 11:29:15AM +0800, Wei Wang wrote: > > > On 01/25/2018 09:41 PM, Michael S. Tsirkin wrote: > > > > On Wed, Jan 24, 2018 at 06:42:41PM +0800, Wei Wang wrote: > > > 2) If worse, all the blocks have been split into smaller blocks and > > > used after the caller comes back. > > > > > > where could we continue? > > > > I'm not sure. But an alternative appears to be to hold a lock and just > > block whoever wanted to use any pages. Yes we are sending hints > > faster but apparently something wanted these pages, and holding the > > lock is interfering with this something. > > I've been thinking about it. How about the following scheme: > 1. register balloon to get a (new) callback when free list runs empty 2. take > pages off the free list, add them to the balloon specific list 3. report to > host 4. > readd to free list at tail 5. if callback triggers, interrupt balloon > reporting to > host, >and readd to free list at tail So in step 2, when we walk through the free page list, take each block, and add them to the balloon specific list, is this performed under the mm lock? If it is still under the lock, then what would be the difference compared to walking through the free list, and add each block to virtqueue? Best, Wei ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
RE: [PATCH v24 1/2] mm: support reporting free page blocks
On Friday, January 26, 2018 11:00 PM, Michael S. Tsirkin wrote:
> On Fri, Jan 26, 2018 at 11:29:15AM +0800, Wei Wang wrote:
> > On 01/25/2018 09:41 PM, Michael S. Tsirkin wrote:
> > > On Wed, Jan 24, 2018 at 06:42:41PM +0800, 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.
> > > >
> > > > Signed-off-by: Wei Wang
> > > > Signed-off-by: Liang Li
> > > > Cc: Michal Hocko
> > > > Cc: Michael S. Tsirkin
> > > > Acked-by: Michal Hocko
> > > > ---
> > > > include/linux/mm.h | 6
> > > > mm/page_alloc.c| 91
> ++
> > > > 2 files changed, 97 insertions(+)
> > > >
> > > > diff --git a/include/linux/mm.h b/include/linux/mm.h index
> > > > ea818ff..b3077dd 100644
> > > > --- a/include/linux/mm.h
> > > > +++ b/include/linux/mm.h
> > > > @@ -1938,6 +1938,12 @@ 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_pfn_range)(void *opaque,
> > > > +unsigned long
> > > > pfn,
> > > > +unsigned long
> > > > num));
> > > > +
> > > > /*
> > > >* 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
> > > > 76c9688..705de22 100644
> > > > --- a/mm/page_alloc.c
> > > > +++ b/mm/page_alloc.c
> > > > @@ -4899,6 +4899,97 @@ void show_free_areas(unsigned int filter,
> nodemask_t *nodemask)
> > > > show_swap_cache_info();
> > > > }
> > > > +/*
> > > > + * Walk through a free page list and report the found pfn range
> > > > +via the
> > > > + * callback.
> > > > + *
> > > > + * Return false if the callback requests to stop reporting.
> > > > +Otherwise,
> > > > + * return true.
> > > > + */
> > > > +static bool walk_free_page_list(void *opaque,
> > > > + struct zone *zone,
> > > > + int order,
> > > > + enum migratetype mt,
> > > > + bool (*report_pfn_range)(void *,
> > > > +unsigned long,
> > > > +unsigned long))
> > > > +{
> > > > + struct page *page;
> > > > + struct list_head *list;
> > > > + unsigned long pfn, flags;
> > > > + bool ret;
> > > > +
> > > > + spin_lock_irqsave(&zone->lock, flags);
> > > > + list = &zone->free_area[order].free_list[mt];
> > > > + list_for_each_entry(page, list, lru) {
> > > > + pfn = page_to_pfn(page);
> > > > + ret = report_pfn_range(opaque, pfn, 1 << order);
> > > > + if (!ret)
> > > > + break;
> > > > + }
> > > > + spin_unlock_irqrestore(&zone->lock, flags);
> > > > +
> > > > + return ret;
> > > > +}
> > > There are two issues with this API. One is that it is not
> > > restarteable: if you return false, you start from the beginning. So
> > > no way to drop lock, do something slow and then proceed.
> > >
> > > Another is that you are using it to report free page hints.
> > > Presumably the point is to drop these pages - keeping them near head
> > > of the list and reusing the reported ones will just make everything
> > > slower invalidating the hint.
> > >
> > > How about rotating these pages towards the end of the list?
> > > Probably not on each call, callect reported pages and then move them
> > > to tail when we exit.
> >
> >
> > I'm not sure how this would help. For example, we have a list of 2M
> > free page blocks:
> > A-->B-->C-->D-->E-->F-->G--H
> >
> > After reporting A and B, and put them to the end and exit, when the
> > caller comes back,
> > 1) if the list remains unch
