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tmpfs: add shmem_read_mapping_page_gfp

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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>
This commit is contained in:
Hugh Dickins 2011-06-27 16:18:04 -07:00 committed by Linus Torvalds
parent 94c1e62df4
commit d9d90e5eb7
2 changed files with 33 additions and 7 deletions
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17
include/linux/shmem_fs.h
View File

@ -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

23
mm/shmem.c
View File

@ -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);