From 5c2c2587b13235bf8b5c9027589f22eff68bdf49 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Fri, 15 Jan 2016 16:56:49 -0800 Subject: mm, dax, pmem: introduce {get|put}_dev_pagemap() for dax-gup get_dev_page() enables paths like get_user_pages() to pin a dynamically mapped pfn-range (devm_memremap_pages()) while the resulting struct page objects are in use. Unlike get_page() it may fail if the device is, or is in the process of being, disabled. While the initial lookup of the range may be an expensive list walk, the result is cached to speed up subsequent lookups which are likely to be in the same mapped range. devm_memremap_pages() now requires a reference counter to be specified at init time. For pmem this means moving request_queue allocation into pmem_alloc() so the existing queue usage counter can track "device pages". ZONE_DEVICE pages always have an elevated count and will never be on an lru reclaim list. That space in 'struct page' can be redirected for other uses, but for safety introduce a poison value that will always trip __list_add() to assert. This allows half of the struct list_head storage to be reclaimed with some assurance to back up the assumption that the page count never goes to zero and a list_add() is never attempted. Signed-off-by: Dan Williams Tested-by: Logan Gunthorpe Cc: Dave Hansen Cc: Matthew Wilcox Cc: Ross Zwisler Cc: Alexander Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memremap.h | 49 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 47 insertions(+), 2 deletions(-) (limited to 'include/linux/memremap.h') diff --git a/include/linux/memremap.h b/include/linux/memremap.h index aa3e82a80d7b..bcaa634139a9 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -1,6 +1,8 @@ #ifndef _LINUX_MEMREMAP_H_ #define _LINUX_MEMREMAP_H_ #include +#include +#include struct resource; struct device; @@ -36,21 +38,25 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start) /** * struct dev_pagemap - metadata for ZONE_DEVICE mappings * @altmap: pre-allocated/reserved memory for vmemmap allocations + * @res: physical address range covered by @ref + * @ref: reference count that pins the devm_memremap_pages() mapping * @dev: host device of the mapping for debug */ struct dev_pagemap { struct vmem_altmap *altmap; const struct resource *res; + struct percpu_ref *ref; struct device *dev; }; #ifdef CONFIG_ZONE_DEVICE void *devm_memremap_pages(struct device *dev, struct resource *res, - struct vmem_altmap *altmap); + struct percpu_ref *ref, struct vmem_altmap *altmap); struct dev_pagemap *find_dev_pagemap(resource_size_t phys); #else static inline void *devm_memremap_pages(struct device *dev, - struct resource *res, struct vmem_altmap *altmap) + struct resource *res, struct percpu_ref *ref, + struct vmem_altmap *altmap) { /* * Fail attempts to call devm_memremap_pages() without @@ -66,4 +72,43 @@ static inline struct dev_pagemap *find_dev_pagemap(resource_size_t phys) return NULL; } #endif + +/** + * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn + * @pfn: page frame number to lookup page_map + * @pgmap: optional known pgmap that already has a reference + * + * @pgmap allows the overhead of a lookup to be bypassed when @pfn lands in the + * same mapping. + */ +static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn, + struct dev_pagemap *pgmap) +{ + const struct resource *res = pgmap ? pgmap->res : NULL; + resource_size_t phys = PFN_PHYS(pfn); + + /* + * In the cached case we're already holding a live reference so + * we can simply do a blind increment + */ + if (res && phys >= res->start && phys <= res->end) { + percpu_ref_get(pgmap->ref); + return pgmap; + } + + /* fall back to slow path lookup */ + rcu_read_lock(); + pgmap = find_dev_pagemap(phys); + if (pgmap && !percpu_ref_tryget_live(pgmap->ref)) + pgmap = NULL; + rcu_read_unlock(); + + return pgmap; +} + +static inline void put_dev_pagemap(struct dev_pagemap *pgmap) +{ + if (pgmap) + percpu_ref_put(pgmap->ref); +} #endif /* _LINUX_MEMREMAP_H_ */ -- cgit v1.2.1