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 now a shmem_read_mapping_page_gfp() ready for that transition,
and a shmem_read_mapping_page() inline for its 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.)
Tidy up the nearby declarations in pagemap.h.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
---
include/linux/pagemap.h | 22 +++++++++++++++-------
mm/shmem.c | 23 +++++++++++++++++++++++
2 files changed, 38 insertions(+), 7 deletions(-)
--- linux.orig/include/linux/pagemap.h 2011-05-30 13:56:10.212797101 -0700
+++ linux/include/linux/pagemap.h 2011-05-30 14:25:32.665536626 -0700
@@ -255,31 +255,39 @@ static inline struct page *grab_cache_pa
extern struct page * grab_cache_page_nowait(struct address_space *mapping,
pgoff_t index);
extern struct page * read_cache_page_async(struct address_space *mapping,
- pgoff_t index, filler_t *filler,
- void *data);
+ pgoff_t index, filler_t *filler, void *data);
extern struct page * read_cache_page(struct address_space *mapping,
- pgoff_t index, filler_t *filler,
- void *data);
+ pgoff_t index, filler_t *filler, void *data);
extern struct page * read_cache_page_gfp(struct address_space *mapping,
pgoff_t index, gfp_t gfp_mask);
extern int read_cache_pages(struct address_space *mapping,
struct list_head *pages, filler_t *filler, void *data);
static inline struct page *read_mapping_page_async(
- struct address_space *mapping,
- pgoff_t index, void *data)
+ struct address_space *mapping,
+ pgoff_t index, void *data)
{
filler_t *filler = (filler_t *)mapping->a_ops->readpage;
return read_cache_page_async(mapping, index, filler, data);
}
static inline struct page *read_mapping_page(struct address_space *mapping,
- pgoff_t index, void *data)
+ pgoff_t index, void *data)
{
filler_t *filler = (filler_t *)mapping->a_ops->readpage;
return read_cache_page(mapping, index, filler, data);
}
+extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
+ pgoff_t index, gfp_t gfp_mask);
+
+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));
+}
+
/*
* Return byte-offset into filesystem object for page.
*/
--- linux.orig/mm/shmem.c 2011-05-30 14:13:03.569821995 -0700
+++ linux/mm/shmem.c 2011-05-30 14:25:32.665536626 -0700
@@ -3028,3 +3028,26 @@ int shmem_zero_setup(struct vm_area_stru
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);
--
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