1 files changed, 278 insertions, 72 deletions

diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
index 063d994bda0b..b41a7d7e20f0 100644
--- a/fs/ext3/balloc.c
+++ b/fs/ext3/balloc.c
@@ -38,6 +38,13 @@
 
 #define in_range(b, first, len) ((b) >= (first) && (b) <= (first) + (len) - 1)
 
+/**
+ * ext3_get_group_desc() -- load group descriptor from disk
+ * @sb:                 super block
+ * @block_group:        given block group
+ * @bh:                 pointer to the buffer head to store the block
+ *                      group descriptor
+ */
 struct ext3_group_desc * ext3_get_group_desc(struct super_block * sb,
                                              unsigned int block_group,
                                              struct buffer_head ** bh)
@@ -73,8 +80,12 @@ struct ext3_group_desc * ext3_get_group_desc(struct super_block * sb,
         return desc + offset;
 }
 
-/*
- * Read the bitmap for a given block_group, reading into the specified 
+/**
+ * read_block_bitmap()
+ * @sb:                 super block
+ * @block_group:        given block group
+ *
+ * Read the bitmap for a given block_group, reading into the specified
  * slot in the superblock's bitmap cache.
  *
  * Return buffer_head on success or NULL in case of failure.
@@ -103,15 +114,22 @@ error_out:
  * Operations include:
  * dump, find, add, remove, is_empty, find_next_reservable_window, etc.
  *
- * We use sorted double linked list for the per-filesystem reservation
- * window list. (like in vm_region).
+ * We use a red-black tree to represent per-filesystem reservation
+ * windows.
+ *
+ */
+
+/**
+ * __rsv_window_dump() -- Dump the filesystem block allocation reservation map
+ * @rb_root:            root of per-filesystem reservation rb tree
+ * @verbose:            verbose mode
+ * @fn:                 function which wishes to dump the reservation map
  *
- * Initially, we keep those small operations in the abstract functions,
- * so later if we need a better searching tree than double linked-list,
- * we could easily switch to that without changing too much
- * code.
+ * If verbose is turned on, it will print the whole block reservation
+ * windows(start, end). Otherwise, it will only print out the "bad" windows,
+ * those windows that overlap with their immediate neighbors.
  */
-#if 0
+#if 1
 static void __rsv_window_dump(struct rb_root *root, int verbose,
                               const char *fn)
 {
@@ -129,7 +147,7 @@ restart:
                 rsv = list_entry(n, struct ext3_reserve_window_node, rsv_node);
                 if (verbose)
                         printk("reservation window 0x%p "
-                               "start:  %d, end:  %d\n",
+                               "start:  %lu, end:  %lu\n",
                                rsv, rsv->rsv_start, rsv->rsv_end);
                 if (rsv->rsv_start && rsv->rsv_start >= rsv->rsv_end) {
                         printk("Bad reservation %p (start >= end)\n",
@@ -161,6 +179,22 @@ restart:
 #define rsv_window_dump(root, verbose) do {} while (0)
 #endif
 
+/**
+ * goal_in_my_reservation()
+ * @rsv:                inode's reservation window
+ * @grp_goal:           given goal block relative to the allocation block group
+ * @group:              the current allocation block group
+ * @sb:                 filesystem super block
+ *
+ * Test if the given goal block (group relative) is within the file's
+ * own block reservation window range.
+ *
+ * If the reservation window is outside the goal allocation group, return 0;
+ * grp_goal (given goal block) could be -1, which means no specific
+ * goal block. In this case, always return 1.
+ * If the goal block is within the reservation window, return 1;
+ * otherwise, return 0;
+ */
 static int
 goal_in_my_reservation(struct ext3_reserve_window *rsv, ext3_grpblk_t grp_goal,
                         unsigned int group, struct super_block * sb)
@@ -168,7 +202,7 @@ goal_in_my_reservation(struct ext3_reserve_window *rsv, ext3_grpblk_t grp_goal,
         ext3_fsblk_t group_first_block, group_last_block;
 
         group_first_block = ext3_group_first_block_no(sb, group);
-        group_last_block = group_first_block + EXT3_BLOCKS_PER_GROUP(sb) - 1;
+        group_last_block = group_first_block + (EXT3_BLOCKS_PER_GROUP(sb) - 1);
 
         if ((rsv->_rsv_start > group_last_block) ||
             (rsv->_rsv_end < group_first_block))
@@ -179,7 +213,11 @@ goal_in_my_reservation(struct ext3_reserve_window *rsv, ext3_grpblk_t grp_goal,
         return 1;
 }
 
-/*
+/**
+ * search_reserve_window()
+ * @rb_root:            root of reservation tree
+ * @goal:               target allocation block
+ *
  * Find the reserved window which includes the goal, or the previous one
  * if the goal is not in any window.
  * Returns NULL if there are no windows or if all windows start after the goal.
@@ -216,6 +254,13 @@ search_reserve_window(struct rb_root *root, ext3_fsblk_t goal)
         return rsv;
 }
 
+/**
+ * ext3_rsv_window_add() -- Insert a window to the block reservation rb tree.
+ * @sb:                 super block
+ * @rsv:                reservation window to add
+ *
+ * Must be called with rsv_lock hold.
+ */
 void ext3_rsv_window_add(struct super_block *sb,
                     struct ext3_reserve_window_node *rsv)
 {
@@ -236,14 +281,25 @@ void ext3_rsv_window_add(struct super_block *sb,
                         p = &(*p)->rb_left;
                 else if (start > this->rsv_end)
                         p = &(*p)->rb_right;
-                else
+                else {
+                        rsv_window_dump(root, 1);
                         BUG();
+                }
         }
 
         rb_link_node(node, parent, p);
         rb_insert_color(node, root);
 }
 
+/**
+ * ext3_rsv_window_remove() -- unlink a window from the reservation rb tree
+ * @sb:                 super block
+ * @rsv:                reservation window to remove
+ *
+ * Mark the block reservation window as not allocated, and unlink it
+ * from the filesystem reservation window rb tree. Must be called with
+ * rsv_lock hold.
+ */
 static void rsv_window_remove(struct super_block *sb,
                               struct ext3_reserve_window_node *rsv)
 {
@@ -253,11 +309,39 @@ static void rsv_window_remove(struct super_block *sb,
         rb_erase(&rsv->rsv_node, &EXT3_SB(sb)->s_rsv_window_root);
 }
 
+/*
+ * rsv_is_empty() -- Check if the reservation window is allocated.
+ * @rsv:                given reservation window to check
+ *
+ * returns 1 if the end block is EXT3_RESERVE_WINDOW_NOT_ALLOCATED.
+ */
 static inline int rsv_is_empty(struct ext3_reserve_window *rsv)
 {
         /* a valid reservation end block could not be 0 */
-        return (rsv->_rsv_end == EXT3_RESERVE_WINDOW_NOT_ALLOCATED);
+        return rsv->_rsv_end == EXT3_RESERVE_WINDOW_NOT_ALLOCATED;
 }
+
+/**
+ * ext3_init_block_alloc_info()
+ * @inode:              file inode structure
+ *
+ * Allocate and initialize the  reservation window structure, and
+ * link the window to the ext3 inode structure at last
+ *
+ * The reservation window structure is only dynamically allocated
+ * and linked to ext3 inode the first time the open file
+ * needs a new block. So, before every ext3_new_block(s) call, for
+ * regular files, we should check whether the reservation window
+ * structure exists or not. In the latter case, this function is called.
+ * Fail to do so will result in block reservation being turned off for that
+ * open file.
+ *
+ * This function is called from ext3_get_blocks_handle(), also called
+ * when setting the reservation window size through ioctl before the file
+ * is open for write (needs block allocation).
+ *
+ * Needs truncate_mutex protection prior to call this function.
+ */
 void ext3_init_block_alloc_info(struct inode *inode)
 {
         struct ext3_inode_info *ei = EXT3_I(inode);
@@ -271,7 +355,7 @@ void ext3_init_block_alloc_info(struct inode *inode)
                 rsv->rsv_start = EXT3_RESERVE_WINDOW_NOT_ALLOCATED;
                 rsv->rsv_end = EXT3_RESERVE_WINDOW_NOT_ALLOCATED;
 
-                /*
+                /*
                  * if filesystem is mounted with NORESERVATION, the goal
                  * reservation window size is set to zero to indicate
                  * block reservation is off
@@ -287,6 +371,19 @@ void ext3_init_block_alloc_info(struct inode *inode)
         ei->i_block_alloc_info = block_i;
 }
 
+/**
+ * ext3_discard_reservation()
+ * @inode:              inode
+ *
+ * Discard(free) block reservation window on last file close, or truncate
+ * or at last iput().
+ *
+ * It is being called in three cases:
+ *      ext3_release_file(): last writer close the file
+ *      ext3_clear_inode(): last iput(), when nobody link to this file.
+ *      ext3_truncate(): when the block indirect map is about to change.
+ *
+ */
 void ext3_discard_reservation(struct inode *inode)
 {
         struct ext3_inode_info *ei = EXT3_I(inode);
@@ -306,7 +403,14 @@ void ext3_discard_reservation(struct inode *inode)
         }
 }
 
-/* Free given blocks, update quota and i_blocks field */
+/**
+ * ext3_free_blocks_sb() -- Free given blocks and update quota
+ * @handle:                     handle to this transaction
+ * @sb:                         super block
+ * @block:                      start physcial block to free
+ * @count:                      number of blocks to free
+ * @pdquot_freed_blocks:        pointer to quota
+ */
 void ext3_free_blocks_sb(handle_t *handle, struct super_block *sb,
                          ext3_fsblk_t block, unsigned long count,
                          unsigned long *pdquot_freed_blocks)
@@ -419,8 +523,8 @@ do_more:
                 }
                 /* @@@ This prevents newly-allocated data from being
                  * freed and then reallocated within the same
-                 * transaction. 
-                 * 
+                 * transaction.
+                 *
                  * Ideally we would want to allow that to happen, but to
                  * do so requires making journal_forget() capable of
                  * revoking the queued write of a data block, which
@@ -433,7 +537,7 @@ do_more:
                  * safe not to set the allocation bit in the committed
                  * bitmap, because we know that there is no outstanding
                  * activity on the buffer any more and so it is safe to
-                 * reallocate it.  
+                 * reallocate it.
                  */
                 BUFFER_TRACE(bitmap_bh, "set in b_committed_data");
                 J_ASSERT_BH(bitmap_bh,
@@ -490,7 +594,13 @@ error_return:
         return;
 }
 
-/* Free given blocks, update quota and i_blocks field */
+/**
+ * ext3_free_blocks() -- Free given blocks and update quota
+ * @handle:             handle for this transaction
+ * @inode:              inode
+ * @block:              start physical block to free
+ * @count:              number of blocks to count
+ */
 void ext3_free_blocks(handle_t *handle, struct inode *inode,
                         ext3_fsblk_t block, unsigned long count)
 {
@@ -508,7 +618,11 @@ void ext3_free_blocks(handle_t *handle, struct inode *inode,
         return;
 }
 
-/*
+/**
+ * ext3_test_allocatable()
+ * @nr:                 given allocation block group
+ * @bh:                 bufferhead contains the bitmap of the given block group
+ *
  * For ext3 allocations, we must not reuse any blocks which are
  * allocated in the bitmap buffer's "last committed data" copy.  This
  * prevents deletes from freeing up the page for reuse until we have
@@ -518,7 +632,7 @@ void ext3_free_blocks(handle_t *handle, struct inode *inode,
  * data would allow the old block to be overwritten before the
  * transaction committed (because we force data to disk before commit).
  * This would lead to corruption if we crashed between overwriting the
- * data and committing the delete. 
+ * data and committing the delete.
  *
  * @@@ We may want to make this allocation behaviour conditional on
  * data-writes at some point, and disable it for metadata allocations or
@@ -541,6 +655,16 @@ static int ext3_test_allocatable(ext3_grpblk_t nr, struct buffer_head *bh)
         return ret;
 }
 
+/**
+ * bitmap_search_next_usable_block()
+ * @start:              the starting block (group relative) of the search
+ * @bh:                 bufferhead contains the block group bitmap
+ * @maxblocks:          the ending block (group relative) of the reservation
+ *
+ * The bitmap search --- search forward alternately through the actual
+ * bitmap on disk and the last-committed copy in journal, until we find a
+ * bit free in both bitmaps.
+ */
 static ext3_grpblk_t
 bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
                                         ext3_grpblk_t maxblocks)
@@ -548,11 +672,6 @@ bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
         ext3_grpblk_t next;
         struct journal_head *jh = bh2jh(bh);
 
-        /*
-         * The bitmap search --- search forward alternately through the actual
-         * bitmap and the last-committed copy until we find a bit free in
-         * both
-         */
         while (start < maxblocks) {
                 next = ext3_find_next_zero_bit(bh->b_data, maxblocks, start);
                 if (next >= maxblocks)
@@ -562,14 +681,20 @@ bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
                 jbd_lock_bh_state(bh);
                 if (jh->b_committed_data)
                         start = ext3_find_next_zero_bit(jh->b_committed_data,
-                                                        maxblocks, next);
+                                                        maxblocks, next);
                 jbd_unlock_bh_state(bh);
         }
         return -1;
 }
 
-/*
- * Find an allocatable block in a bitmap.  We honour both the bitmap and
+/**
+ * find_next_usable_block()
+ * @start:              the starting block (group relative) to find next
+ *                      allocatable block in bitmap.
+ * @bh:                 bufferhead contains the block group bitmap
+ * @maxblocks:          the ending block (group relative) for the search
+ *
+ * Find an allocatable block in a bitmap.  We honor both the bitmap and
  * its last-committed copy (if that exists), and perform the "most
  * appropriate allocation" algorithm of looking for a free block near
  * the initial goal; then for a free byte somewhere in the bitmap; then
@@ -584,7 +709,7 @@ find_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
 
         if (start > 0) {
                 /*
-                 * The goal was occupied; search forward for a free 
+                 * The goal was occupied; search forward for a free
                  * block within the next XX blocks.
                  *
                  * end_goal is more or less random, but it has to be
@@ -620,7 +745,11 @@ find_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
         return here;
 }
 
-/*
+/**
+ * claim_block()
+ * @block:              the free block (group relative) to allocate
+ * @bh:                 the bufferhead containts the block group bitmap
+ *
  * We think we can allocate this block in this bitmap.  Try to set the bit.
  * If that succeeds then check that nobody has allocated and then freed the
  * block since we saw that is was not marked in b_committed_data.  If it _was_
@@ -646,7 +775,26 @@ claim_block(spinlock_t *lock, ext3_grpblk_t block, struct buffer_head *bh)
         return ret;
 }
 
-/*
+/**
+ * ext3_try_to_allocate()
+ * @sb:                 superblock
+ * @handle:             handle to this transaction
+ * @group:              given allocation block group
+ * @bitmap_bh:          bufferhead holds the block bitmap
+ * @grp_goal:           given target block within the group
+ * @count:              target number of blocks to allocate
+ * @my_rsv:             reservation window
+ *
+ * Attempt to allocate blocks within a give range. Set the range of allocation
+ * first, then find the first free bit(s) from the bitmap (within the range),
+ * and at last, allocate the blocks by claiming the found free bit as allocated.
+ *
+ * To set the range of this allocation:
+ *      if there is a reservation window, only try to allocate block(s) from the
+ *      file's own reservation window;
+ *      Otherwise, the allocation range starts from the give goal block, ends at
+ *      the block group's last block.
+ *
  * If we failed to allocate the desired block then we may end up crossing to a
  * new bitmap.  In that case we must release write access to the old one via
  * ext3_journal_release_buffer(), else we'll run out of credits.
@@ -703,7 +851,8 @@ repeat:
         }
         start = grp_goal;
 
-        if (!claim_block(sb_bgl_lock(EXT3_SB(sb), group), grp_goal, bitmap_bh)) {
+        if (!claim_block(sb_bgl_lock(EXT3_SB(sb), group),
+                grp_goal, bitmap_bh)) {
                 /*
                  * The block was allocated by another thread, or it was
                  * allocated and then freed by another thread
@@ -718,7 +867,8 @@ repeat:
         grp_goal++;
         while (num < *count && grp_goal < end
                 && ext3_test_allocatable(grp_goal, bitmap_bh)
-                && claim_block(sb_bgl_lock(EXT3_SB(sb), group), grp_goal, bitmap_bh)) {
+                && claim_block(sb_bgl_lock(EXT3_SB(sb), group),
+                                grp_goal, bitmap_bh)) {
                 num++;
                 grp_goal++;
         }
@@ -730,12 +880,12 @@ fail_access:
 }
 
 /**
- *      find_next_reservable_window():
+ *      find_next_reservable_window():
  *              find a reservable space within the given range.
  *              It does not allocate the reservation window for now:
  *              alloc_new_reservation() will do the work later.
  *
- *      @search_head: the head of the searching list;
+ *      @search_head: the head of the searching list;
  *              This is not necessarily the list head of the whole filesystem
  *
  *              We have both head and start_block to assist the search
@@ -743,12 +893,12 @@ fail_access:
  *              but we will shift to the place where start_block is,
  *              then start from there, when looking for a reservable space.
  *
- *      @size: the target new reservation window size
+ *      @size: the target new reservation window size
  *
- *      @group_first_block: the first block we consider to start
+ *      @group_first_block: the first block we consider to start
  *                      the real search from
  *
- *      @last_block:
+ *      @last_block:
  *              the maximum block number that our goal reservable space
  *              could start from. This is normally the last block in this
  *              group. The search will end when we found the start of next
@@ -756,10 +906,10 @@ fail_access:
  *              This could handle the cross boundary reservation window
  *              request.
  *
- *      basically we search from the given range, rather than the whole
- *      reservation double linked list, (start_block, last_block)
- *      to find a free region that is of my size and has not
- *      been reserved.
+ *      basically we search from the given range, rather than the whole
+ *      reservation double linked list, (start_block, last_block)
+ *      to find a free region that is of my size and has not
+ *      been reserved.
  *
  */
 static int find_next_reservable_window(
@@ -812,7 +962,7 @@ static int find_next_reservable_window(
                         /*
                          * Found a reserveable space big enough.  We could
                          * have a reservation across the group boundary here
-                         */
+                         */
                         break;
                 }
         }
@@ -848,7 +998,7 @@ static int find_next_reservable_window(
 }
 
 /**
- *      alloc_new_reservation()--allocate a new reservation window
+ *      alloc_new_reservation()--allocate a new reservation window
  *
  *              To make a new reservation, we search part of the filesystem
  *              reservation list (the list that inside the group). We try to
@@ -897,7 +1047,7 @@ static int alloc_new_reservation(struct ext3_reserve_window_node *my_rsv,
         spinlock_t *rsv_lock = &EXT3_SB(sb)->s_rsv_window_lock;
 
         group_first_block = ext3_group_first_block_no(sb, group);
-        group_end_block = group_first_block + EXT3_BLOCKS_PER_GROUP(sb) - 1;
+        group_end_block = group_first_block + (EXT3_BLOCKS_PER_GROUP(sb) - 1);
 
         if (grp_goal < 0)
                 start_block = group_first_block;
@@ -929,9 +1079,10 @@ static int alloc_new_reservation(struct ext3_reserve_window_node *my_rsv,
                 if ((my_rsv->rsv_alloc_hit >
                      (my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
                         /*
-                         * if we previously allocation hit ration is greater than half
-                         * we double the size of reservation window next time
-                         * otherwise keep the same
+                         * if the previously allocation hit ratio is
+                         * greater than 1/2, then we double the size of
+                         * the reservation window the next time,
+                         * otherwise we keep the same size window
                          */
                         size = size * 2;
                         if (size > EXT3_MAX_RESERVE_BLOCKS)
@@ -1010,6 +1161,23 @@ retry:
         goto retry;
 }
 
+/**
+ * try_to_extend_reservation()
+ * @my_rsv:             given reservation window
+ * @sb:                 super block
+ * @size:               the delta to extend
+ *
+ * Attempt to expand the reservation window large enough to have
+ * required number of free blocks
+ *
+ * Since ext3_try_to_allocate() will always allocate blocks within
+ * the reservation window range, if the window size is too small,
+ * multiple blocks allocation has to stop at the end of the reservation
+ * window. To make this more efficient, given the total number of
+ * blocks needed and the current size of the window, we try to
+ * expand the reservation window size if necessary on a best-effort
+ * basis before ext3_new_blocks() tries to allocate blocks,
+ */
 static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
                         struct super_block *sb, int size)
 {
@@ -1035,7 +1203,17 @@ static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
         spin_unlock(rsv_lock);
 }
 
-/*
+/**
+ * ext3_try_to_allocate_with_rsv()
+ * @sb:                 superblock
+ * @handle:             handle to this transaction
+ * @group:              given allocation block group
+ * @bitmap_bh:          bufferhead holds the block bitmap
+ * @grp_goal:           given target block within the group
+ * @count:              target number of blocks to allocate
+ * @my_rsv:             reservation window
+ * @errp:               pointer to store the error code
+ *
  * This is the main function used to allocate a new block and its reservation
  * window.
  *
@@ -1051,9 +1229,7 @@ static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
  * reservation), and there are lots of free blocks, but they are all
  * being reserved.
  *
- * We use a sorted double linked list for the per-filesystem reservation list.
- * The insert, remove and find a free space(non-reserved) operations for the
- * sorted double linked list should be fast.
+ * We use a red-black tree for the per-filesystem reservation list.
  *
  */
 static ext3_grpblk_t
@@ -1063,7 +1239,7 @@ ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
                         struct ext3_reserve_window_node * my_rsv,
                         unsigned long *count, int *errp)
 {
-        ext3_fsblk_t group_first_block;
+        ext3_fsblk_t group_first_block, group_last_block;
         ext3_grpblk_t ret = 0;
         int fatal;
         unsigned long num = *count;
@@ -1100,6 +1276,7 @@ ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
          * first block is the block number of the first block in this group
          */
         group_first_block = ext3_group_first_block_no(sb, group);
+        group_last_block = group_first_block + (EXT3_BLOCKS_PER_GROUP(sb) - 1);
 
         /*
          * Basically we will allocate a new block from inode's reservation
@@ -1118,7 +1295,8 @@ ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
          */
         while (1) {
                 if (rsv_is_empty(&my_rsv->rsv_window) || (ret < 0) ||
-                        !goal_in_my_reservation(&my_rsv->rsv_window, grp_goal, group, sb)) {
+                        !goal_in_my_reservation(&my_rsv->rsv_window,
+                                                grp_goal, group, sb)) {
                         if (my_rsv->rsv_goal_size < *count)
                                 my_rsv->rsv_goal_size = *count;
                         ret = alloc_new_reservation(my_rsv, grp_goal, sb,
@@ -1126,17 +1304,21 @@ ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
                         if (ret < 0)
                                 break;                  /* failed */
 
-                        if (!goal_in_my_reservation(&my_rsv->rsv_window, grp_goal, group, sb))
+                        if (!goal_in_my_reservation(&my_rsv->rsv_window,
+                                                        grp_goal, group, sb))
                                 grp_goal = -1;
-                } else if (grp_goal > 0 && (my_rsv->rsv_end-grp_goal+1) < *count)
+                } else if (grp_goal > 0 &&
+                          (my_rsv->rsv_end-grp_goal+1) < *count)
                         try_to_extend_reservation(my_rsv, sb,
                                         *count-my_rsv->rsv_end + grp_goal - 1);
 
-                if ((my_rsv->rsv_start >= group_first_block + EXT3_BLOCKS_PER_GROUP(sb))
-                    || (my_rsv->rsv_end < group_first_block))
+                if ((my_rsv->rsv_start > group_last_block) ||
+                                (my_rsv->rsv_end < group_first_block)) {
+                        rsv_window_dump(&EXT3_SB(sb)->s_rsv_window_root, 1);
                         BUG();
-                ret = ext3_try_to_allocate(sb, handle, group, bitmap_bh, grp_goal,
-                                           &num, &my_rsv->rsv_window);
+                }
+                ret = ext3_try_to_allocate(sb, handle, group, bitmap_bh,
+                                           grp_goal, &num, &my_rsv->rsv_window);
                 if (ret >= 0) {
                         my_rsv->rsv_alloc_hit += num;
                         *count = num;
@@ -1161,6 +1343,12 @@ out:
         return ret;
 }
 
+/**
+ * ext3_has_free_blocks()
+ * @sbi:                in-core super block structure.
+ *
+ * Check if filesystem has at least 1 free block available for allocation.
+ */
 static int ext3_has_free_blocks(struct ext3_sb_info *sbi)
 {
         ext3_fsblk_t free_blocks, root_blocks;
@@ -1175,11 +1363,17 @@ static int ext3_has_free_blocks(struct ext3_sb_info *sbi)
         return 1;
 }
 
-/*
+/**
+ * ext3_should_retry_alloc()
+ * @sb:                 super block
+ * @retries             number of attemps has been made
+ *
  * ext3_should_retry_alloc() is called when ENOSPC is returned, and if
  * it is profitable to retry the operation, this function will wait
  * for the current or commiting transaction to complete, and then
  * return TRUE.
+ *
+ * if the total number of retries exceed three times, return FALSE.
  */
 int ext3_should_retry_alloc(struct super_block *sb, int *retries)
 {
@@ -1191,13 +1385,19 @@ int ext3_should_retry_alloc(struct super_block *sb, int *retries)
         return journal_force_commit_nested(EXT3_SB(sb)->s_journal);
 }
 
-/*
- * ext3_new_block uses a goal block to assist allocation.  If the goal is
- * free, or there is a free block within 32 blocks of the goal, that block
- * is allocated.  Otherwise a forward search is made for a free block; within 
- * each block group the search first looks for an entire free byte in the block
- * bitmap, and then for any free bit if that fails.
- * This function also updates quota and i_blocks field.
+/**
+ * ext3_new_blocks() -- core block(s) allocation function
+ * @handle:             handle to this transaction
+ * @inode:              file inode
+ * @goal:               given target block(filesystem wide)
+ * @count:              target number of blocks to allocate
+ * @errp:               error code
+ *
+ * ext3_new_blocks uses a goal block to assist allocation.  It tries to
+ * allocate block(s) from the block group contains the goal block first. If that
+ * fails, it will try to allocate block(s) from other block groups without
+ * any specific goal block.
+ *
  */
 ext3_fsblk_t ext3_new_blocks(handle_t *handle, struct inode *inode,
                         ext3_fsblk_t goal, unsigned long *count, int *errp)
@@ -1303,7 +1503,7 @@ retry_alloc:
         smp_rmb();
 
         /*
-         * Now search the rest of the groups.  We assume that 
+         * Now search the rest of the groups.  We assume that
          * i and gdp correctly point to the last group visited.
          */
         for (bgi = 0; bgi < ngroups; bgi++) {
@@ -1428,7 +1628,7 @@ allocated:
 
         spin_lock(sb_bgl_lock(sbi, group_no));
         gdp->bg_free_blocks_count =
-                        cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count) - num);
+                        cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)-num);
         spin_unlock(sb_bgl_lock(sbi, group_no));
         percpu_counter_mod(&sbi->s_freeblocks_counter, -num);
 
@@ -1471,6 +1671,12 @@ ext3_fsblk_t ext3_new_block(handle_t *handle, struct inode *inode,
         return ext3_new_blocks(handle, inode, goal, &count, errp);
 }
 
+/**
+ * ext3_count_free_blocks() -- count filesystem free blocks
+ * @sb:         superblock
+ *
+ * Adds up the number of free blocks from each block group.
+ */
 ext3_fsblk_t ext3_count_free_blocks(struct super_block *sb)
 {
         ext3_fsblk_t desc_count;