vfs: pagecache usage optimization for pagesize!=blocksize

[safe/jmp/linux-2.6] / fs / buffer.c

diff --git a/fs/buffer.c b/fs/buffer.c
index f958050..ca12a6b 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2096,6 +2096,52 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 EXPORT_SYMBOL(generic_write_end);
 
 /*
+ * block_is_partially_uptodate checks whether buffers within a page are
+ * uptodate or not.
+ *
+ * Returns true if all buffers which correspond to a file portion
+ * we want to read are uptodate.
+ */
+int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
+                                       unsigned long from)
+{
+       struct inode *inode = page->mapping->host;
+       unsigned block_start, block_end, blocksize;
+       unsigned to;
+       struct buffer_head *bh, *head;
+       int ret = 1;
+
+       if (!page_has_buffers(page))
+               return 0;
+
+       blocksize = 1 << inode->i_blkbits;
+       to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
+       to = from + to;
+       if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
+               return 0;
+
+       head = page_buffers(page);
+       bh = head;
+       block_start = 0;
+       do {
+               block_end = block_start + blocksize;
+               if (block_end > from && block_start < to) {
+                       if (!buffer_uptodate(bh)) {
+                               ret = 0;
+                               break;
+                       }
+                       if (block_end >= to)
+                               break;
+               }
+               block_start = block_end;
+               bh = bh->b_this_page;
+       } while (bh != head);
+
+       return ret;
+}
+EXPORT_SYMBOL(block_is_partially_uptodate);
+
+/*
  * Generic "read page" function for block devices that have the normal
  * get_block functionality. This is most of the block device filesystems.
  * Reads the page asynchronously --- the unlock_buffer() and