Re: [PATCH v16 4/5] mm: support reporting free page blocks
On Sat 30-09-17 12:05:53, 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 46b9ac5..d9652c2 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1835,6 +1835,12 @@ 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 6d00f74..c6bb874 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4762,6 +4762,97 @@ 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(>lock, flags); > + list = >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(>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
Re: [PATCH v16 4/5] mm: support reporting free page blocks
On Sat 30-09-17 12:05:53, 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 46b9ac5..d9652c2 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1835,6 +1835,12 @@ 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 6d00f74..c6bb874 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4762,6 +4762,97 @@ 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(>lock, flags); > + list = >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(>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, >