tmpfs: add shmem_read_mapping_page_gfp

Although it is used (by i915) on nothing but tmpfs, read_cache_page_gfp() is unsuited to tmpfs, because it inserts a page into pagecache before calling the filesystem's ->readpage: tmpfs may have pages in swapcache which only it knows how to locate and switch to filecache. At present tmpfs provides a ->readpage method, and copes with this by copying pages; but soon we can simplify it by removing its ->readpage. Provide shmem_read_mapping_page_gfp() now, ready for that transition, Export shmem_read_mapping_page_gfp() and add it to list in shmem_fs.h, with shmem_read_mapping_page() inline for the common mapping_gfp case. (shmem_read_mapping_page_gfp or shmem_read_cache_page_gfp? Generally the read_mapping_page functions use the mapping's ->readpage, and the read_cache_page functions use the supplied filler, so I think read_cache_page_gfp was slightly misnamed.) Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tmpfs: add shmem_read_mapping_page_gfp
Although it is used (by i915) on nothing but tmpfs, read_cache_page_gfp() is unsuited to tmpfs, because it inserts a page into pagecache before calling the filesystem's ->readpage: tmpfs may have pages in swapcache which only it knows how to locate and switch to filecache. At present tmpfs provides a ->readpage method, and copes with this by copying pages; but soon we can simplify it by removing its ->readpage. Provide shmem_read_mapping_page_gfp() now, ready for that transition, Export shmem_read_mapping_page_gfp() and add it to list in shmem_fs.h, with shmem_read_mapping_page() inline for the common mapping_gfp case. (shmem_read_mapping_page_gfp or shmem_read_cache_page_gfp? Generally the read_mapping_page functions use the mapping's ->readpage, and the read_cache_page functions use the supplied filler, so I think read_cache_page_gfp was slightly misnamed.) Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Hugh Dickins · Linus Torvalds
1 parent 94c1e62df4
Showing 2 changed files with 33 additions and 7 deletions Side-by-side Diff
include/linux/shmem_fs.h
mm/shmem.c
@@ -3,15 +3,9 @@
  
 #include <linux/swap.h>
 #include <linux/mempolicy.h>
+#include <linux/pagemap.h>
 #include <linux/percpu_counter.h>
  
-struct page;
-struct file;
-struct inode;
-struct super_block;
-struct user_struct;
-struct vm_area_struct;
-
 /* inode in-kernel data */
  
 #define SHMEM_NR_DIRECT 16
  
@@ -61,10 +55,19 @@
 					loff_t size, unsigned long flags);
 extern int shmem_zero_setup(struct vm_area_struct *);
 extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
+					pgoff_t index, gfp_t gfp_mask);
 extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
 extern int shmem_unuse(swp_entry_t entry, struct page *page);
 extern void mem_cgroup_get_shmem_target(struct inode *inode, pgoff_t pgoff,
 					struct page **pagep, swp_entry_t *ent);
+
+static inline struct page *shmem_read_mapping_page(
+				struct address_space *mapping, pgoff_t index)
+{
+	return shmem_read_mapping_page_gfp(mapping, index,
+					mapping_gfp_mask(mapping));
+}
  
 #endif
@@ -3035,4 +3035,27 @@
 	vma->vm_flags |= VM_CAN_NONLINEAR;
 	return 0;
 }
+
+/**
+ * shmem_read_mapping_page_gfp - read into page cache, using specified page allocation flags.
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @gfp:	the page allocator flags to use if allocating
+ *
+ * This behaves as a tmpfs "read_cache_page_gfp(mapping, index, gfp)",
+ * with any new page allocations done using the specified allocation flags.
+ * But read_cache_page_gfp() uses the ->readpage() method: which does not
+ * suit tmpfs, since it may have pages in swapcache, and needs to find those
+ * for itself; although drivers/gpu/drm i915 and ttm rely upon this support.
+ *
+ * Provide a stub for those callers to start using now, then later
+ * flesh it out to call shmem_getpage() with additional gfp mask, when
+ * shmem_file_splice_read() is added and shmem_readpage() is removed.
+ */
+struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
+					 pgoff_t index, gfp_t gfp)
+{
+	return read_cache_page_gfp(mapping, index, gfp);
+}
+EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
...	...	@@ -3,15 +3,9 @@
3	3
4	4	#include <linux/swap.h>
5	5	#include <linux/mempolicy.h>
	6	+#include <linux/pagemap.h>
6	7	#include <linux/percpu_counter.h>
7	8
8		-struct page;
9		-struct file;
10		-struct inode;
11		-struct super_block;
12		-struct user_struct;
13		-struct vm_area_struct;
14		-
15	9	/* inode in-kernel data */
16	10
17	11	#define SHMEM_NR_DIRECT 16
18	12
...	...	@@ -61,10 +55,19 @@
61	55	loff_t size, unsigned long flags);
62	56	extern int shmem_zero_setup(struct vm_area_struct *);
63	57	extern int shmem_lock(struct file file, int lock, struct user_struct user);
	58	+extern struct page shmem_read_mapping_page_gfp(struct address_space mapping,
	59	+ pgoff_t index, gfp_t gfp_mask);
64	60	extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
65	61	extern int shmem_unuse(swp_entry_t entry, struct page *page);
66	62	extern void mem_cgroup_get_shmem_target(struct inode *inode, pgoff_t pgoff,
67	63	struct page *pagep, swp_entry_t ent);
	64	+
	65	+static inline struct page *shmem_read_mapping_page(
	66	+ struct address_space *mapping, pgoff_t index)
	67	+{
	68	+ return shmem_read_mapping_page_gfp(mapping, index,
	69	+ mapping_gfp_mask(mapping));
	70	+}
68	71
69	72	#endif
...	...	@@ -3035,4 +3035,27 @@
3035	3035	vma->vm_flags \|= VM_CAN_NONLINEAR;
3036	3036	return 0;
3037	3037	}
	3038	+
	3039	+/**
	3040	+ * shmem_read_mapping_page_gfp - read into page cache, using specified page allocation flags.
	3041	+ * @mapping: the page's address_space
	3042	+ * @index: the page index
	3043	+ * @gfp: the page allocator flags to use if allocating
	3044	+ *
	3045	+ * This behaves as a tmpfs "read_cache_page_gfp(mapping, index, gfp)",
	3046	+ * with any new page allocations done using the specified allocation flags.
	3047	+ * But read_cache_page_gfp() uses the ->readpage() method: which does not
	3048	+ * suit tmpfs, since it may have pages in swapcache, and needs to find those
	3049	+ * for itself; although drivers/gpu/drm i915 and ttm rely upon this support.
	3050	+ *
	3051	+ * Provide a stub for those callers to start using now, then later
	3052	+ * flesh it out to call shmem_getpage() with additional gfp mask, when
	3053	+ * shmem_file_splice_read() is added and shmem_readpage() is removed.
	3054	+ */
	3055	+struct page shmem_read_mapping_page_gfp(struct address_space mapping,
	3056	+ pgoff_t index, gfp_t gfp)
	3057	+{
	3058	+ return read_cache_page_gfp(mapping, index, gfp);
	3059	+}
	3060	+EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);