ext4: Add new abstraction ext4_map_blocks() underneath ext4_get_blocks()

Jack up ext4_get_blocks() and add a new function, ext4_map_blocks()
which uses a much smaller structure, struct ext4_map_blocks which is
20 bytes, as opposed to a struct buffer_head, which nearly 5 times
bigger on an x86_64 machine.  By switching things to use
ext4_map_blocks(), we can save stack space by using ext4_map_blocks()
since we can avoid allocating a struct buffer_head on the stack.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 58 insertions, 44 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 830336d3911b..ff2f5fd681b5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -149,7 +149,7 @@ int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
         int ret;
 
         /*
-         * Drop i_data_sem to avoid deadlock with ext4_get_blocks At this
+         * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
          * moment, get_block can be called only for blocks inside i_size since
          * page cache has been already dropped and writes are blocked by
          * i_mutex. So we can safely drop the i_data_sem here.
@@ -890,9 +890,9 @@ err_out:
 }
 
 /*
- * The ext4_ind_get_blocks() function handles non-extents inodes
+ * The ext4_ind_map_blocks() function handles non-extents inodes
  * (i.e., using the traditional indirect/double-indirect i_blocks
- * scheme) for ext4_get_blocks().
+ * scheme) for ext4_map_blocks().
  *
  * Allocation strategy is simple: if we have to allocate something, we will
  * have to go the whole way to leaf. So let's do it before attaching anything
@@ -917,9 +917,8 @@ err_out:
  * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system
  * blocks.
  */
-static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
-                               ext4_lblk_t iblock, unsigned int maxblocks,
-                               struct buffer_head *bh_result,
+static int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
+                               struct ext4_map_blocks *map,
                                int flags)
 {
         int err = -EIO;
@@ -935,7 +934,7 @@ static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
 
         J_ASSERT(!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL));
         J_ASSERT(handle != NULL || (flags & EXT4_GET_BLOCKS_CREATE) == 0);
-        depth = ext4_block_to_path(inode, iblock, offsets,
+        depth = ext4_block_to_path(inode, map->m_lblk, offsets,
                                    &blocks_to_boundary);
 
         if (depth == 0)
@@ -946,10 +945,9 @@ static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
         /* Simplest case - block found, no allocation needed */
         if (!partial) {
                 first_block = le32_to_cpu(chain[depth - 1].key);
-                clear_buffer_new(bh_result);
                 count++;
                 /*map more blocks*/
-                while (count < maxblocks && count <= blocks_to_boundary) {
+                while (count < map->m_len && count <= blocks_to_boundary) {
                         ext4_fsblk_t blk;
 
                         blk = le32_to_cpu(*(chain[depth-1].p + count));
@@ -969,7 +967,7 @@ static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
         /*
          * Okay, we need to do block allocation.
         */
-        goal = ext4_find_goal(inode, iblock, partial);
+        goal = ext4_find_goal(inode, map->m_lblk, partial);
 
         /* the number of blocks need to allocate for [d,t]indirect blocks */
         indirect_blks = (chain + depth) - partial - 1;
@@ -979,11 +977,11 @@ static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
          * direct blocks to allocate for this branch.
          */
         count = ext4_blks_to_allocate(partial, indirect_blks,
-                                        maxblocks, blocks_to_boundary);
+                                      map->m_len, blocks_to_boundary);
         /*
          * Block out ext4_truncate while we alter the tree
          */
-        err = ext4_alloc_branch(handle, inode, iblock, indirect_blks,
+        err = ext4_alloc_branch(handle, inode, map->m_lblk, indirect_blks,
                                 &count, goal,
                                 offsets + (partial - chain), partial);
 
@@ -995,18 +993,20 @@ static int ext4_ind_get_blocks(handle_t *handle, struct inode *inode,
          * may need to return -EAGAIN upwards in the worst case.  --sct
          */
         if (!err)
-                err = ext4_splice_branch(handle, inode, iblock,
+                err = ext4_splice_branch(handle, inode, map->m_lblk,
                                          partial, indirect_blks, count);
         if (err)
                 goto cleanup;
 
-        set_buffer_new(bh_result);
+        map->m_flags |= EXT4_MAP_NEW;
 
         ext4_update_inode_fsync_trans(handle, inode, 1);
 got_it:
-        map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
+        map->m_flags |= EXT4_MAP_MAPPED;
+        map->m_pblk = le32_to_cpu(chain[depth-1].key);
+        map->m_len = count;
         if (count > blocks_to_boundary)
-                set_buffer_boundary(bh_result);
+                map->m_flags |= EXT4_MAP_BOUNDARY;
         err = count;
         /* Clean up and exit */
         partial = chain + depth - 1;    /* the whole chain */
@@ -1016,7 +1016,6 @@ cleanup:
                 brelse(partial->bh);
                 partial--;
         }
-        BUFFER_TRACE(bh_result, "returned");
 out:
         return err;
 }
@@ -1203,15 +1202,15 @@ static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
 }
 
 /*
- * The ext4_get_blocks() function tries to look up the requested blocks,
+ * The ext4_map_blocks() function tries to look up the requested blocks,
  * and returns if the blocks are already mapped.
  *
  * Otherwise it takes the write lock of the i_data_sem and allocate blocks
  * and store the allocated blocks in the result buffer head and mark it
  * mapped.
  *
- * If file type is extents based, it will call ext4_ext_get_blocks(),
- * Otherwise, call with ext4_ind_get_blocks() to handle indirect mapping
+ * If file type is extents based, it will call ext4_ext_map_blocks(),
+ * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
  * based files
  *
  * On success, it returns the number of blocks being mapped or allocate.
@@ -1224,35 +1223,30 @@ static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
  *
  * It returns the error in case of allocation failure.
  */
-int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
-                    unsigned int max_blocks, struct buffer_head *bh,
-                    int flags)
+int ext4_map_blocks(handle_t *handle, struct inode *inode,
+                    struct ext4_map_blocks *map, int flags)
 {
         int retval;
 
-        clear_buffer_mapped(bh);
-        clear_buffer_unwritten(bh);
-
-        ext_debug("ext4_get_blocks(): inode %lu, flag %d, max_blocks %u,"
-                  "logical block %lu\n", inode->i_ino, flags, max_blocks,
-                  (unsigned long)block);
+        map->m_flags = 0;
+        ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
+                  "logical block %lu\n", inode->i_ino, flags, map->m_len,
+                  (unsigned long) map->m_lblk);
         /*
          * Try to see if we can get the block without requesting a new
          * file system block.
          */
         down_read((&EXT4_I(inode)->i_data_sem));
         if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
-                retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
-                                bh, 0);
+                retval = ext4_ext_map_blocks(handle, inode, map, 0);
         } else {
-                retval = ext4_ind_get_blocks(handle, inode, block, max_blocks,
-                                             bh, 0);
+                retval = ext4_ind_map_blocks(handle, inode, map, 0);
         }
         up_read((&EXT4_I(inode)->i_data_sem));
 
-        if (retval > 0 && buffer_mapped(bh)) {
+        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                 int ret = check_block_validity(inode, "file system corruption",
-                                               block, bh->b_blocknr, retval);
+                                        map->m_lblk, map->m_pblk, retval);
                 if (ret != 0)
                         return ret;
         }
@@ -1268,7 +1262,7 @@ int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
          * ext4_ext_get_block() returns th create = 0
          * with buffer head unmapped.
          */
-        if (retval > 0 && buffer_mapped(bh))
+        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
                 return retval;
 
         /*
@@ -1281,7 +1275,7 @@ int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
          * of BH_Unwritten and BH_Mapped flags being simultaneously
          * set on the buffer_head.
          */
-        clear_buffer_unwritten(bh);
+        map->m_flags &= ~EXT4_MAP_UNWRITTEN;
 
         /*
          * New blocks allocate and/or writing to uninitialized extent
@@ -1304,13 +1298,11 @@ int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
          * could have changed the inode type in between
          */
         if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
-                retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
-                                              bh, flags);
+                retval = ext4_ext_map_blocks(handle, inode, map, flags);
         } else {
-                retval = ext4_ind_get_blocks(handle, inode, block,
-                                             max_blocks, bh, flags);
+                retval = ext4_ind_map_blocks(handle, inode, map, flags);
 
-                if (retval > 0 && buffer_new(bh)) {
+                if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
                         /*
                          * We allocated new blocks which will result in
                          * i_data's format changing.  Force the migrate
@@ -1333,16 +1325,38 @@ int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
                 EXT4_I(inode)->i_delalloc_reserved_flag = 0;
 
         up_write((&EXT4_I(inode)->i_data_sem));
-        if (retval > 0 && buffer_mapped(bh)) {
+        if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
                 int ret = check_block_validity(inode, "file system "
                                                "corruption after allocation",
-                                               block, bh->b_blocknr, retval);
+                                               map->m_lblk, map->m_pblk,
+                                               retval);
                 if (ret != 0)
                         return ret;
         }
         return retval;
 }
 
+int ext4_get_blocks(handle_t *handle, struct inode *inode, sector_t block,
+                    unsigned int max_blocks, struct buffer_head *bh,
+                    int flags)
+{
+        struct ext4_map_blocks map;
+        int ret;
+
+        map.m_lblk = block;
+        map.m_len = max_blocks;
+
+        ret = ext4_map_blocks(handle, inode, &map, flags);
+        if (ret < 0)
+                return ret;
+
+        bh->b_blocknr = map.m_pblk;
+        bh->b_size = inode->i_sb->s_blocksize * map.m_len;
+        bh->b_bdev = inode->i_sb->s_bdev;
+        bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
+        return ret;
+}
+
 /* Maximum number of blocks we map for direct IO at once. */
 #define DIO_MAX_BLOCKS 4096