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 <[email protected]> --- Matthew Wilcox, Ira Weiny, and others have complained that ZONE_DEVICE struct page reference counting is ugly/broken. This is my attempt to fix it and it works for the HMM migration self tests. I'm only sending this out as a RFC since I'm not that familiar with the DAX, PMEM, XEN, and other uses of ZONE_DEVICE struct pages allocated with devm_memremap_pages() or memremap_pages() but my best reading of the code looks like it might be OK. I could use help testing these configurations. I have a modified THP migration patch series that applies on top of this one and is cleaner since I don't have to add code to handle the +1 reference count. The link below is for the earlier v2: ("mm/hmm/nouveau: add THP migration to migrate_vma_*") https://lore.kernel.org/linux-mm/[email protected] arch/powerpc/kvm/book3s_hv_uvmem.c | 1 - drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 - include/linux/memremap.h | 6 +-- include/linux/mm.h | 39 --------------- lib/test_hmm.c | 1 - mm/gup.c | 44 ----------------- mm/memremap.c | 20 ++++---- mm/migrate.c | 5 -- mm/swap.c | 66 +++++++++++--------------- 9 files changed, 41 insertions(+), 142 deletions(-) diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c index 84e5a2dc8be5..00d97050d7ff 100644 --- a/arch/powerpc/kvm/book3s_hv_uvmem.c +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c @@ -711,7 +711,6 @@ 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); 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 a13c6215bba8..2a4bbe01a455 100644 --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c @@ -324,7 +324,6 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm) return NULL; } - get_page(page); lock_page(page); return page; } diff --git a/include/linux/memremap.h b/include/linux/memremap.h index 4e9c738f4b31..7dd9802d2612 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -67,9 +67,9 @@ 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 is + * reset to 1 before calling page_free(). 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 517751310dd2..5a82037a4b26 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1093,34 +1093,6 @@ static inline bool is_zone_device_page(const struct page *page) #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(&devmap_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) @@ -1169,17 +1141,6 @@ 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)) __put_page(page); } diff --git a/lib/test_hmm.c b/lib/test_hmm.c index c8133f50160b..5410f7328577 100644 --- a/lib/test_hmm.c +++ b/lib/test_hmm.c @@ -561,7 +561,6 @@ static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice) } dpage->zone_device_data = rpage; - get_page(dpage); lock_page(dpage); return dpage; diff --git a/mm/gup.c b/mm/gup.c index b9b1cd8bcd6a..3c54f0c190a3 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -177,41 +177,6 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags) return true; } -#ifdef CONFIG_DEV_PAGEMAP_OPS -static bool __unpin_devmap_managed_user_page(struct page *page) -{ - int count, refs = 1; - - if (!page_is_devmap_managed(page)) - return false; - - if (hpage_pincount_available(page)) - hpage_pincount_sub(page, 1); - else - refs = GUP_PIN_COUNTING_BIAS; - - count = page_ref_sub_return(page, refs); - - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED, 1); - /* - * devmap page refcounts are 1-based, rather than 0-based: if - * refcount is 1, then the page is free and the refcount is - * stable because nobody holds a reference on the page. - */ - if (count == 1) - free_devmap_managed_page(page); - else if (!count) - __put_page(page); - - return true; -} -#else -static bool __unpin_devmap_managed_user_page(struct page *page) -{ - return false; -} -#endif /* CONFIG_DEV_PAGEMAP_OPS */ - /** * unpin_user_page() - release a dma-pinned page * @page: pointer to page to be released @@ -227,15 +192,6 @@ void unpin_user_page(struct page *page) page = compound_head(page); - /* - * For devmap managed pages we need to catch refcount transition from - * GUP_PIN_COUNTING_BIAS 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 (__unpin_devmap_managed_user_page(page)) - return; - if (hpage_pincount_available(page)) hpage_pincount_sub(page, 1); else diff --git a/mm/memremap.c b/mm/memremap.c index 9c951bbfee91..f09562789079 100644 --- a/mm/memremap.c +++ b/mm/memremap.c @@ -91,13 +91,6 @@ static unsigned long pfn_end(struct dev_pagemap *pgmap, int range_id) return (range->start + range_len(range)) >> PAGE_SHIFT; } -static unsigned long pfn_next(unsigned long pfn) -{ - if (pfn % 1024 == 0) - cond_resched(); - return pfn + 1; -} - /* * This returns true if the page is reserved by ZONE_DEVICE driver. */ @@ -176,13 +169,12 @@ static void pageunmap_range(struct dev_pagemap *pgmap, int range_id) void memunmap_pages(struct dev_pagemap *pgmap) { - unsigned long pfn; int i; dev_pagemap_kill(pgmap); for (i = 0; i < pgmap->nr_range; i++) - for_each_device_pfn(pfn, pgmap, i) - put_page(pfn_to_page(pfn)); + percpu_ref_put_many(pgmap->ref, pfn_end(pgmap, i) - + pfn_first(pgmap, i)); dev_pagemap_cleanup(pgmap); for (i = 0; i < pgmap->nr_range; i++) @@ -516,6 +508,14 @@ void free_devmap_managed_page(struct page *page) mem_cgroup_uncharge(page); + /* + * ZONE_DEVICE drivers keep a reference to the page while it is on + * the driver's free list so we reset the reference count here. + * This matches the initial reference when the struct pages are + * created by memremap_pages(). + */ + set_page_refcounted(page); + /* * When a device_private page is freed, the page->mapping field * may still contain a (stale) mapping value. For example, the diff --git a/mm/migrate.c b/mm/migrate.c index 4f89360d9e77..be1586582b52 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -380,11 +380,6 @@ static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; - /* - * Device private pages have an extra refcount as they are - * ZONE_DEVICE pages. - */ - expected_count += is_device_private_page(page); if (mapping) expected_count += thp_nr_pages(page) + page_has_private(page); diff --git a/mm/swap.c b/mm/swap.c index feff680d3de9..8468e72e397f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -113,10 +113,31 @@ static void __put_compound_page(struct page *page) destroy_compound_page(page); } +#ifdef CONFIG_DEV_PAGEMAP_OPS +static void __put_devmap_managed_page(struct page *page) +{ + if (!static_branch_unlikely(&devmap_managed_key)) + return; + + switch (page->pgmap->type) { + case MEMORY_DEVICE_PRIVATE: + case MEMORY_DEVICE_FS_DAX: + free_devmap_managed_page(page); + break; + default: + break; + } +} +#else +static inline void __put_devmap_managed_page(struct page *page) +{ +} +#endif + void __put_page(struct page *page) { if (is_zone_device_page(page)) { - put_dev_pagemap(page->pgmap); + __put_devmap_managed_page(page); /* * The page belongs to the device that created pgmap. Do @@ -851,27 +872,19 @@ void release_pages(struct page **pages, int nr) if (is_huge_zero_page(page)) continue; + page = compound_head(page); + if (!put_page_testzero(page)) + continue; + if (is_zone_device_page(page)) { if (locked_pgdat) { spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags); locked_pgdat = NULL; } - /* - * ZONE_DEVICE pages that return 'false' from - * put_devmap_managed_page() do not require special - * processing, and instead, expect a call to - * put_page_testzero(). - */ - if (page_is_devmap_managed(page)) { - put_devmap_managed_page(page); - continue; - } - } - - page = compound_head(page); - if (!put_page_testzero(page)) + __put_devmap_managed_page(page); continue; + } if (PageCompound(page)) { if (locked_pgdat) { @@ -1149,26 +1162,3 @@ void __init swap_setup(void) * _really_ don't want to cluster much more */ } - -#ifdef CONFIG_DEV_PAGEMAP_OPS -void put_devmap_managed_page(struct page *page) -{ - int count; - - if (WARN_ON_ONCE(!page_is_devmap_managed(page))) - return; - - count = page_ref_dec_return(page); - - /* - * devmap page refcounts are 1-based, rather than 0-based: if - * refcount is 1, then the page is free and the refcount is - * stable because nobody holds a reference on the page. - */ - if (count == 1) - free_devmap_managed_page(page); - else if (!count) - __put_page(page); -} -EXPORT_SYMBOL(put_devmap_managed_page); -#endif -- 2.20.1
