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Commit d9d90e5e authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 94c1e62d

include/linux/shmem_fs.h

+10 −7
Original line number Diff line number Diff line
@@ -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
@@ -61,9 +55,18 @@ extern struct file *shmem_file_setup(const char *name, 
					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

mm/shmem.c

+23 −0
Original line number Diff line number Diff line
@@ -3035,3 +3035,26 @@ int shmem_zero_setup(struct vm_area_struct *vma) 
	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);