Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
On Fri, Sep 25, 2020 at 01:44:42PM -0700, Ralph Campbell wrote: > ZONE_DEVICE struct pages have an extra reference count that complicates the > code for put_page() and several places in the kernel that need to check the > reference count to see that a page is not being used (gup, compaction, > migration, etc.). Clean up the code so the reference count doesn't need to > be treated specially for ZONE_DEVICE. > > Signed-off-by: Ralph Campbell > --- > arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- > drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- > include/linux/dax.h| 2 +- > include/linux/memremap.h | 7 ++- > include/linux/mm.h | 44 -- > lib/test_hmm.c | 2 +- > mm/gup.c | 44 -- > mm/internal.h | 8 +++ > mm/memremap.c | 82 ++ > mm/migrate.c | 5 -- > mm/page_alloc.c| 3 + > mm/swap.c | 46 +++ > 12 files changed, 44 insertions(+), 203 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c > b/arch/powerpc/kvm/book3s_hv_uvmem.c > index 7705d5557239..e6ec98325fab 100644 > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c > @@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long > gpa, struct kvm *kvm) > > dpage = pfn_to_page(uvmem_pfn); > dpage->zone_device_data = pvt; > - get_page(dpage); > + init_page_count(dpage); The powerpc change looks good. Passes a quick sanity test of booting/rebooting a secure guest on Power. Tested-by: Bharata B Rao Regards, Bharata.
Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
On 9/25/20 11:41 PM, Christoph Hellwig wrote: On Fri, Sep 25, 2020 at 01:44:42PM -0700, Ralph Campbell wrote: ZONE_DEVICE struct pages have an extra reference count that complicates the code for put_page() and several places in the kernel that need to check the reference count to see that a page is not being used (gup, compaction, migration, etc.). Clean up the code so the reference count doesn't need to be treated specially for ZONE_DEVICE. Signed-off-by: Ralph Campbell --- arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- include/linux/dax.h| 2 +- include/linux/memremap.h | 7 ++- include/linux/mm.h | 44 -- lib/test_hmm.c | 2 +- mm/gup.c | 44 -- mm/internal.h | 8 +++ mm/memremap.c | 82 ++ mm/migrate.c | 5 -- mm/page_alloc.c| 3 + mm/swap.c | 46 +++ 12 files changed, 44 insertions(+), 203 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c index 7705d5557239..e6ec98325fab 100644 --- a/arch/powerpc/kvm/book3s_hv_uvmem.c +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c @@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm) dpage = pfn_to_page(uvmem_pfn); dpage->zone_device_data = pvt; - get_page(dpage); + init_page_count(dpage); lock_page(dpage); return dpage; out_clear: diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c index 4e8112fde3e6..ca2e3c3edc36 100644 --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c @@ -323,7 +323,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm) return NULL; } - get_page(page); + init_page_count(page); lock_page(page); return page; } diff --git a/include/linux/dax.h b/include/linux/dax.h index 3f78ed78d1d6..8d29f38645aa 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -240,7 +240,7 @@ static inline bool dax_mapping(struct address_space *mapping) static inline bool dax_layout_is_idle_page(struct page *page) { - return page_ref_count(page) <= 1; + return page_ref_count(page) == 0; } #endif diff --git a/include/linux/memremap.h b/include/linux/memremap.h index e5862746751b..f9224f88e4cd 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -65,9 +65,10 @@ enum memory_type { struct dev_pagemap_ops { /* -* Called once the page refcount reaches 1. (ZONE_DEVICE pages never -* reach 0 refcount unless there is a refcount bug. This allows the -* device driver to implement its own memory management.) +* Called once the page refcount reaches 0. The reference count +* should be reset to one with init_page_count(page) before reusing +* the page. This allows the device driver to implement its own +* memory management. */ void (*page_free)(struct page *page); diff --git a/include/linux/mm.h b/include/linux/mm.h index b2f370f0b420..2159c2477aa3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1092,39 +1092,6 @@ static inline bool is_zone_device_page(const struct page *page) } #endif -#ifdef CONFIG_DEV_PAGEMAP_OPS -void free_devmap_managed_page(struct page *page); -DECLARE_STATIC_KEY_FALSE(devmap_managed_key); - -static inline bool page_is_devmap_managed(struct page *page) -{ - if (!static_branch_unlikely(_managed_key)) - return false; - if (!is_zone_device_page(page)) - return false; - switch (page->pgmap->type) { - case MEMORY_DEVICE_PRIVATE: - case MEMORY_DEVICE_FS_DAX: - return true; - default: - break; - } - return false; -} - -void put_devmap_managed_page(struct page *page); - -#else /* CONFIG_DEV_PAGEMAP_OPS */ -static inline bool page_is_devmap_managed(struct page *page) -{ - return false; -} - -static inline void put_devmap_managed_page(struct page *page) -{ -} -#endif /* CONFIG_DEV_PAGEMAP_OPS */ - static inline bool is_device_private_page(const struct page *page) { return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) && @@ -1171,17 +1138,6 @@ static inline void put_page(struct page *page) { page = compound_head(page); - /* -* For devmap managed pages we need to catch refcount transition from -* 2 to 1, when refcount reach one it means the page is free and we -* need to inform the device driver through callback. See -* include/linux/memremap.h and HMM for details. -*/ - if
Re: [PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
On Fri, Sep 25, 2020 at 01:44:42PM -0700, Ralph Campbell wrote: > ZONE_DEVICE struct pages have an extra reference count that complicates the > code for put_page() and several places in the kernel that need to check the > reference count to see that a page is not being used (gup, compaction, > migration, etc.). Clean up the code so the reference count doesn't need to > be treated specially for ZONE_DEVICE. > > Signed-off-by: Ralph Campbell > --- > arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- > drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- > include/linux/dax.h| 2 +- > include/linux/memremap.h | 7 ++- > include/linux/mm.h | 44 -- > lib/test_hmm.c | 2 +- > mm/gup.c | 44 -- > mm/internal.h | 8 +++ > mm/memremap.c | 82 ++ > mm/migrate.c | 5 -- > mm/page_alloc.c| 3 + > mm/swap.c | 46 +++ > 12 files changed, 44 insertions(+), 203 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c > b/arch/powerpc/kvm/book3s_hv_uvmem.c > index 7705d5557239..e6ec98325fab 100644 > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c > @@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long > gpa, struct kvm *kvm) > > dpage = pfn_to_page(uvmem_pfn); > dpage->zone_device_data = pvt; > - get_page(dpage); > + init_page_count(dpage); > lock_page(dpage); > return dpage; > out_clear: > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c > b/drivers/gpu/drm/nouveau/nouveau_dmem.c > index 4e8112fde3e6..ca2e3c3edc36 100644 > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c > @@ -323,7 +323,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm) > return NULL; > } > > - get_page(page); > + init_page_count(page); > lock_page(page); > return page; > } > diff --git a/include/linux/dax.h b/include/linux/dax.h > index 3f78ed78d1d6..8d29f38645aa 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -240,7 +240,7 @@ static inline bool dax_mapping(struct address_space > *mapping) > > static inline bool dax_layout_is_idle_page(struct page *page) > { > - return page_ref_count(page) <= 1; > + return page_ref_count(page) == 0; > } > > #endif > diff --git a/include/linux/memremap.h b/include/linux/memremap.h > index e5862746751b..f9224f88e4cd 100644 > --- a/include/linux/memremap.h > +++ b/include/linux/memremap.h > @@ -65,9 +65,10 @@ enum memory_type { > > struct dev_pagemap_ops { > /* > - * Called once the page refcount reaches 1. (ZONE_DEVICE pages never > - * reach 0 refcount unless there is a refcount bug. This allows the > - * device driver to implement its own memory management.) > + * Called once the page refcount reaches 0. The reference count > + * should be reset to one with init_page_count(page) before reusing > + * the page. This allows the device driver to implement its own > + * memory management. >*/ > void (*page_free)(struct page *page); > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b2f370f0b420..2159c2477aa3 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1092,39 +1092,6 @@ static inline bool is_zone_device_page(const struct > page *page) > } > #endif > > -#ifdef CONFIG_DEV_PAGEMAP_OPS > -void free_devmap_managed_page(struct page *page); > -DECLARE_STATIC_KEY_FALSE(devmap_managed_key); > - > -static inline bool page_is_devmap_managed(struct page *page) > -{ > - if (!static_branch_unlikely(_managed_key)) > - return false; > - if (!is_zone_device_page(page)) > - return false; > - switch (page->pgmap->type) { > - case MEMORY_DEVICE_PRIVATE: > - case MEMORY_DEVICE_FS_DAX: > - return true; > - default: > - break; > - } > - return false; > -} > - > -void put_devmap_managed_page(struct page *page); > - > -#else /* CONFIG_DEV_PAGEMAP_OPS */ > -static inline bool page_is_devmap_managed(struct page *page) > -{ > - return false; > -} > - > -static inline void put_devmap_managed_page(struct page *page) > -{ > -} > -#endif /* CONFIG_DEV_PAGEMAP_OPS */ > - > static inline bool is_device_private_page(const struct page *page) > { > return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) && > @@ -1171,17 +1138,6 @@ static inline void put_page(struct page *page) > { > page = compound_head(page); > > - /* > - * For devmap managed pages we need to catch refcount transition from > - * 2 to 1, when refcount reach one it means the page is free and we > - * need to inform the device driver through callback.
[PATCH 2/2] mm: remove extra ZONE_DEVICE struct page refcount
ZONE_DEVICE struct pages have an extra reference count that complicates the code for put_page() and several places in the kernel that need to check the reference count to see that a page is not being used (gup, compaction, migration, etc.). Clean up the code so the reference count doesn't need to be treated specially for ZONE_DEVICE. Signed-off-by: Ralph Campbell --- arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- include/linux/dax.h| 2 +- include/linux/memremap.h | 7 ++- include/linux/mm.h | 44 -- lib/test_hmm.c | 2 +- mm/gup.c | 44 -- mm/internal.h | 8 +++ mm/memremap.c | 82 ++ mm/migrate.c | 5 -- mm/page_alloc.c| 3 + mm/swap.c | 46 +++ 12 files changed, 44 insertions(+), 203 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c index 7705d5557239..e6ec98325fab 100644 --- a/arch/powerpc/kvm/book3s_hv_uvmem.c +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c @@ -711,7 +711,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm) dpage = pfn_to_page(uvmem_pfn); dpage->zone_device_data = pvt; - get_page(dpage); + init_page_count(dpage); lock_page(dpage); return dpage; out_clear: diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c index 4e8112fde3e6..ca2e3c3edc36 100644 --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c @@ -323,7 +323,7 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm) return NULL; } - get_page(page); + init_page_count(page); lock_page(page); return page; } diff --git a/include/linux/dax.h b/include/linux/dax.h index 3f78ed78d1d6..8d29f38645aa 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -240,7 +240,7 @@ static inline bool dax_mapping(struct address_space *mapping) static inline bool dax_layout_is_idle_page(struct page *page) { - return page_ref_count(page) <= 1; + return page_ref_count(page) == 0; } #endif diff --git a/include/linux/memremap.h b/include/linux/memremap.h index e5862746751b..f9224f88e4cd 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -65,9 +65,10 @@ enum memory_type { struct dev_pagemap_ops { /* -* Called once the page refcount reaches 1. (ZONE_DEVICE pages never -* reach 0 refcount unless there is a refcount bug. This allows the -* device driver to implement its own memory management.) +* Called once the page refcount reaches 0. The reference count +* should be reset to one with init_page_count(page) before reusing +* the page. This allows the device driver to implement its own +* memory management. */ void (*page_free)(struct page *page); diff --git a/include/linux/mm.h b/include/linux/mm.h index b2f370f0b420..2159c2477aa3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1092,39 +1092,6 @@ static inline bool is_zone_device_page(const struct page *page) } #endif -#ifdef CONFIG_DEV_PAGEMAP_OPS -void free_devmap_managed_page(struct page *page); -DECLARE_STATIC_KEY_FALSE(devmap_managed_key); - -static inline bool page_is_devmap_managed(struct page *page) -{ - if (!static_branch_unlikely(_managed_key)) - return false; - if (!is_zone_device_page(page)) - return false; - switch (page->pgmap->type) { - case MEMORY_DEVICE_PRIVATE: - case MEMORY_DEVICE_FS_DAX: - return true; - default: - break; - } - return false; -} - -void put_devmap_managed_page(struct page *page); - -#else /* CONFIG_DEV_PAGEMAP_OPS */ -static inline bool page_is_devmap_managed(struct page *page) -{ - return false; -} - -static inline void put_devmap_managed_page(struct page *page) -{ -} -#endif /* CONFIG_DEV_PAGEMAP_OPS */ - static inline bool is_device_private_page(const struct page *page) { return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) && @@ -1171,17 +1138,6 @@ static inline void put_page(struct page *page) { page = compound_head(page); - /* -* For devmap managed pages we need to catch refcount transition from -* 2 to 1, when refcount reach one it means the page is free and we -* need to inform the device driver through callback. See -* include/linux/memremap.h and HMM for details. -*/ - if (page_is_devmap_managed(page)) { - put_devmap_managed_page(page); - return; - } - if (put_page_testzero(page))