[PATCH] map multiple blocks for mpage_readpages()

This patch changes mpage_readpages() and get_block() to get the disk mapping
information for multiple blocks at the same time.

b_size represents the amount of disk mapping that needs to mapped.  On the
successful get_block() b_size indicates the amount of disk mapping thats
actually mapped.  Only the filesystems who care to use this information and
provide multiple disk blocks at a time can choose to do so.

No changes are needed for the filesystems who wants to ignore this.

[akpm@osdl.org: cleanups]
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 85 insertions, 19 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
index 7903b740cc11..9bf2eb30e6f4 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -163,9 +163,19 @@ map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
         } while (page_bh != head);
 }
 
+/*
+ * This is the worker routine which does all the work of mapping the disk
+ * blocks and constructs largest possible bios, submits them for IO if the
+ * blocks are not contiguous on the disk.
+ *
+ * We pass a buffer_head back and forth and use its buffer_mapped() flag to
+ * represent the validity of its disk mapping and to decide when to do the next
+ * get_block() call.
+ */
 static struct bio *
 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
-                        sector_t *last_block_in_bio, get_block_t get_block)
+                sector_t *last_block_in_bio, struct buffer_head *map_bh,
+                unsigned long *first_logical_block, get_block_t get_block)
 {
         struct inode *inode = page->mapping->host;
         const unsigned blkbits = inode->i_blkbits;
@@ -173,34 +183,72 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
         const unsigned blocksize = 1 << blkbits;
         sector_t block_in_file;
         sector_t last_block;
+        sector_t last_block_in_file;
         sector_t blocks[MAX_BUF_PER_PAGE];
         unsigned page_block;
         unsigned first_hole = blocks_per_page;
         struct block_device *bdev = NULL;
-        struct buffer_head bh;
         int length;
         int fully_mapped = 1;
+        unsigned nblocks;
+        unsigned relative_block;
 
         if (page_has_buffers(page))
                 goto confused;
 
         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
-        last_block = (i_size_read(inode) + blocksize - 1) >> blkbits;
+        last_block = block_in_file + nr_pages * blocks_per_page;
+        last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
+        if (last_block > last_block_in_file)
+                last_block = last_block_in_file;
+        page_block = 0;
+
+        /*
+         * Map blocks using the result from the previous get_blocks call first.
+         */
+        nblocks = map_bh->b_size >> blkbits;
+        if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
+                        block_in_file < (*first_logical_block + nblocks)) {
+                unsigned map_offset = block_in_file - *first_logical_block;
+                unsigned last = nblocks - map_offset;
+
+                for (relative_block = 0; ; relative_block++) {
+                        if (relative_block == last) {
+                                clear_buffer_mapped(map_bh);
+                                break;
+                        }
+                        if (page_block == blocks_per_page)
+                                break;
+                        blocks[page_block] = map_bh->b_blocknr + map_offset +
+                                                relative_block;
+                        page_block++;
+                        block_in_file++;
+                }
+                bdev = map_bh->b_bdev;
+        }
+
+        /*
+         * Then do more get_blocks calls until we are done with this page.
+         */
+        map_bh->b_page = page;
+        while (page_block < blocks_per_page) {
+                map_bh->b_state = 0;
+                map_bh->b_size = 0;
 
-        bh.b_page = page;
-        for (page_block = 0; page_block < blocks_per_page;
-                                page_block++, block_in_file++) {
-                bh.b_state = 0;
                 if (block_in_file < last_block) {
-                        bh.b_size = blocksize;
-                        if (get_block(inode, block_in_file, &bh, 0))
+                        map_bh->b_size = (last_block-block_in_file) << blkbits;
+                        if (get_block(inode, block_in_file, map_bh, 0))
                                 goto confused;
+                        *first_logical_block = block_in_file;
                 }
 
-                if (!buffer_mapped(&bh)) {
+                if (!buffer_mapped(map_bh)) {
                         fully_mapped = 0;
                         if (first_hole == blocks_per_page)
                                 first_hole = page_block;
+                        page_block++;
+                        block_in_file++;
+                        clear_buffer_mapped(map_bh);
                         continue;
                 }
 
@@ -210,8 +258,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
                  * we just collected from get_block into the page's buffers
                  * so readpage doesn't have to repeat the get_block call
                  */
-                if (buffer_uptodate(&bh)) {
-                        map_buffer_to_page(page, &bh, page_block);
+                if (buffer_uptodate(map_bh)) {
+                        map_buffer_to_page(page, map_bh, page_block);
                         goto confused;
                 }
         
@@ -219,10 +267,20 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
                         goto confused;          /* hole -> non-hole */
 
                 /* Contiguous blocks? */
-                if (page_block && blocks[page_block-1] != bh.b_blocknr-1)
+                if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
                         goto confused;
-                blocks[page_block] = bh.b_blocknr;
-                bdev = bh.b_bdev;
+                nblocks = map_bh->b_size >> blkbits;
+                for (relative_block = 0; ; relative_block++) {
+                        if (relative_block == nblocks) {
+                                clear_buffer_mapped(map_bh);
+                                break;
+                        } else if (page_block == blocks_per_page)
+                                break;
+                        blocks[page_block] = map_bh->b_blocknr+relative_block;
+                        page_block++;
+                        block_in_file++;
+                }
+                bdev = map_bh->b_bdev;
         }
 
         if (first_hole != blocks_per_page) {
@@ -261,7 +319,7 @@ alloc_new:
                 goto alloc_new;
         }
 
-        if (buffer_boundary(&bh) || (first_hole != blocks_per_page))
+        if (buffer_boundary(map_bh) || (first_hole != blocks_per_page))
                 bio = mpage_bio_submit(READ, bio);
         else
                 *last_block_in_bio = blocks[blocks_per_page - 1];
@@ -332,7 +390,10 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
         unsigned page_idx;
         sector_t last_block_in_bio = 0;
         struct pagevec lru_pvec;
+        struct buffer_head map_bh;
+        unsigned long first_logical_block = 0;
 
+        clear_buffer_mapped(&map_bh);
         pagevec_init(&lru_pvec, 0);
         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
                 struct page *page = list_entry(pages->prev, struct page, lru);
@@ -343,7 +404,9 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
                                         page->index, GFP_KERNEL)) {
                         bio = do_mpage_readpage(bio, page,
                                         nr_pages - page_idx,
-                                        &last_block_in_bio, get_block);
+                                        &last_block_in_bio, &map_bh,
+                                        &first_logical_block,
+                                        get_block);
                         if (!pagevec_add(&lru_pvec, page))
                                 __pagevec_lru_add(&lru_pvec);
                 } else {
@@ -365,9 +428,12 @@ int mpage_readpage(struct page *page, get_block_t get_block)
 {
         struct bio *bio = NULL;
         sector_t last_block_in_bio = 0;
+        struct buffer_head map_bh;
+        unsigned long first_logical_block = 0;
 
-        bio = do_mpage_readpage(bio, page, 1,
-                        &last_block_in_bio, get_block);
+        clear_buffer_mapped(&map_bh);
+        bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
+                        &map_bh, &first_logical_block, get_block);
         if (bio)
                 mpage_bio_submit(READ, bio);
         return 0;