[PATCH] ext3: more comments about block allocation/reservation code
Signed-off-by: Mingming Cao <cmm@us.ibm.com> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Mingming Cao
Linus Torvalds
Родитель
321fb9e818
Коммит
36faadc144
292
fs/ext3/balloc.c
292
fs/ext3/balloc.c
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@ -38,6 +38,13 @@
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#define in_range(b, first, len) ((b) >= (first) && (b) <= (first) + (len) - 1)
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/**
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* ext3_get_group_desc() -- load group descriptor from disk
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* @sb: super block
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* @block_group: given block group
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* @bh: pointer to the buffer head to store the block
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* group descriptor
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*/
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struct ext3_group_desc * ext3_get_group_desc(struct super_block * sb,
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unsigned int block_group,
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struct buffer_head ** bh)
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@ -73,7 +80,11 @@ struct ext3_group_desc * ext3_get_group_desc(struct super_block * sb,
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return desc + offset;
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}
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/*
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/**
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* read_block_bitmap()
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* @sb: super block
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* @block_group: given block group
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*
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* Read the bitmap for a given block_group, reading into the specified
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* slot in the superblock's bitmap cache.
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*
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@ -103,13 +114,20 @@ error_out:
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* Operations include:
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* dump, find, add, remove, is_empty, find_next_reservable_window, etc.
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*
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* We use sorted double linked list for the per-filesystem reservation
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* window list. (like in vm_region).
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* We use a red-black tree to represent per-filesystem reservation
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* windows.
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*
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* Initially, we keep those small operations in the abstract functions,
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* so later if we need a better searching tree than double linked-list,
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* we could easily switch to that without changing too much
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* code.
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*/
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/**
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* __rsv_window_dump() -- Dump the filesystem block allocation reservation map
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* @rb_root: root of per-filesystem reservation rb tree
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* @verbose: verbose mode
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* @fn: function which wishes to dump the reservation map
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*
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* If verbose is turned on, it will print the whole block reservation
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* windows(start, end). Otherwise, it will only print out the "bad" windows,
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* those windows that overlap with their immediate neighbors.
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*/
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#if 1
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static void __rsv_window_dump(struct rb_root *root, int verbose,
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@ -161,6 +179,22 @@ restart:
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#define rsv_window_dump(root, verbose) do {} while (0)
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#endif
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/**
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* goal_in_my_reservation()
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* @rsv: inode's reservation window
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* @grp_goal: given goal block relative to the allocation block group
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* @group: the current allocation block group
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* @sb: filesystem super block
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*
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* Test if the given goal block (group relative) is within the file's
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* own block reservation window range.
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*
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* If the reservation window is outside the goal allocation group, return 0;
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* grp_goal (given goal block) could be -1, which means no specific
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* goal block. In this case, always return 1.
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* If the goal block is within the reservation window, return 1;
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* otherwise, return 0;
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*/
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static int
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goal_in_my_reservation(struct ext3_reserve_window *rsv, ext3_grpblk_t grp_goal,
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unsigned int group, struct super_block * sb)
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@ -179,7 +213,11 @@ goal_in_my_reservation(struct ext3_reserve_window *rsv, ext3_grpblk_t grp_goal,
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return 1;
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}
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/*
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/**
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* search_reserve_window()
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* @rb_root: root of reservation tree
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* @goal: target allocation block
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*
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* Find the reserved window which includes the goal, or the previous one
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* if the goal is not in any window.
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* Returns NULL if there are no windows or if all windows start after the goal.
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@ -216,6 +254,13 @@ search_reserve_window(struct rb_root *root, ext3_fsblk_t goal)
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return rsv;
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}
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/**
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* ext3_rsv_window_add() -- Insert a window to the block reservation rb tree.
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* @sb: super block
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* @rsv: reservation window to add
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*
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* Must be called with rsv_lock hold.
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*/
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void ext3_rsv_window_add(struct super_block *sb,
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struct ext3_reserve_window_node *rsv)
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{
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@ -246,6 +291,15 @@ void ext3_rsv_window_add(struct super_block *sb,
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rb_insert_color(node, root);
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}
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/**
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* ext3_rsv_window_remove() -- unlink a window from the reservation rb tree
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* @sb: super block
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* @rsv: reservation window to remove
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*
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* Mark the block reservation window as not allocated, and unlink it
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* from the filesystem reservation window rb tree. Must be called with
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* rsv_lock hold.
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*/
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static void rsv_window_remove(struct super_block *sb,
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struct ext3_reserve_window_node *rsv)
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{
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@ -255,11 +309,39 @@ static void rsv_window_remove(struct super_block *sb,
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rb_erase(&rsv->rsv_node, &EXT3_SB(sb)->s_rsv_window_root);
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}
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/*
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* rsv_is_empty() -- Check if the reservation window is allocated.
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* @rsv: given reservation window to check
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*
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* returns 1 if the end block is EXT3_RESERVE_WINDOW_NOT_ALLOCATED.
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*/
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static inline int rsv_is_empty(struct ext3_reserve_window *rsv)
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{
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/* a valid reservation end block could not be 0 */
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return (rsv->_rsv_end == EXT3_RESERVE_WINDOW_NOT_ALLOCATED);
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return rsv->_rsv_end == EXT3_RESERVE_WINDOW_NOT_ALLOCATED;
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}
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/**
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* ext3_init_block_alloc_info()
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* @inode: file inode structure
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*
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* Allocate and initialize the reservation window structure, and
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* link the window to the ext3 inode structure at last
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*
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* The reservation window structure is only dynamically allocated
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* and linked to ext3 inode the first time the open file
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* needs a new block. So, before every ext3_new_block(s) call, for
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* regular files, we should check whether the reservation window
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* structure exists or not. In the latter case, this function is called.
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* Fail to do so will result in block reservation being turned off for that
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* open file.
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*
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* This function is called from ext3_get_blocks_handle(), also called
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* when setting the reservation window size through ioctl before the file
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* is open for write (needs block allocation).
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*
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* Needs truncate_mutex protection prior to call this function.
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*/
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void ext3_init_block_alloc_info(struct inode *inode)
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{
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struct ext3_inode_info *ei = EXT3_I(inode);
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@ -289,6 +371,19 @@ void ext3_init_block_alloc_info(struct inode *inode)
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ei->i_block_alloc_info = block_i;
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}
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/**
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* ext3_discard_reservation()
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* @inode: inode
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*
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* Discard(free) block reservation window on last file close, or truncate
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* or at last iput().
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*
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* It is being called in three cases:
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* ext3_release_file(): last writer close the file
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* ext3_clear_inode(): last iput(), when nobody link to this file.
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* ext3_truncate(): when the block indirect map is about to change.
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*
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*/
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void ext3_discard_reservation(struct inode *inode)
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{
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struct ext3_inode_info *ei = EXT3_I(inode);
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@ -308,7 +403,14 @@ void ext3_discard_reservation(struct inode *inode)
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}
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}
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/* Free given blocks, update quota and i_blocks field */
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/**
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* ext3_free_blocks_sb() -- Free given blocks and update quota
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* @handle: handle to this transaction
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* @sb: super block
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* @block: start physcial block to free
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* @count: number of blocks to free
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* @pdquot_freed_blocks: pointer to quota
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*/
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void ext3_free_blocks_sb(handle_t *handle, struct super_block *sb,
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ext3_fsblk_t block, unsigned long count,
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unsigned long *pdquot_freed_blocks)
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@ -492,7 +594,13 @@ error_return:
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return;
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}
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/* Free given blocks, update quota and i_blocks field */
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/**
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* ext3_free_blocks() -- Free given blocks and update quota
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* @handle: handle for this transaction
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* @inode: inode
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* @block: start physical block to free
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* @count: number of blocks to count
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*/
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void ext3_free_blocks(handle_t *handle, struct inode *inode,
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ext3_fsblk_t block, unsigned long count)
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{
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@ -510,7 +618,11 @@ void ext3_free_blocks(handle_t *handle, struct inode *inode,
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return;
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}
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/*
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/**
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* ext3_test_allocatable()
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* @nr: given allocation block group
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* @bh: bufferhead contains the bitmap of the given block group
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*
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* For ext3 allocations, we must not reuse any blocks which are
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* allocated in the bitmap buffer's "last committed data" copy. This
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* prevents deletes from freeing up the page for reuse until we have
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@ -543,6 +655,16 @@ static int ext3_test_allocatable(ext3_grpblk_t nr, struct buffer_head *bh)
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return ret;
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}
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/**
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* bitmap_search_next_usable_block()
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* @start: the starting block (group relative) of the search
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* @bh: bufferhead contains the block group bitmap
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* @maxblocks: the ending block (group relative) of the reservation
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*
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* The bitmap search --- search forward alternately through the actual
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* bitmap on disk and the last-committed copy in journal, until we find a
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* bit free in both bitmaps.
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*/
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static ext3_grpblk_t
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bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
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ext3_grpblk_t maxblocks)
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@ -550,11 +672,6 @@ bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
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ext3_grpblk_t next;
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struct journal_head *jh = bh2jh(bh);
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/*
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* The bitmap search --- search forward alternately through the actual
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* bitmap and the last-committed copy until we find a bit free in
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* both
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*/
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while (start < maxblocks) {
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next = ext3_find_next_zero_bit(bh->b_data, maxblocks, start);
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if (next >= maxblocks)
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@ -570,8 +687,14 @@ bitmap_search_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
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return -1;
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}
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/*
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* Find an allocatable block in a bitmap. We honour both the bitmap and
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/**
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* find_next_usable_block()
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* @start: the starting block (group relative) to find next
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* allocatable block in bitmap.
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* @bh: bufferhead contains the block group bitmap
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* @maxblocks: the ending block (group relative) for the search
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*
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* Find an allocatable block in a bitmap. We honor both the bitmap and
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* its last-committed copy (if that exists), and perform the "most
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* appropriate allocation" algorithm of looking for a free block near
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* the initial goal; then for a free byte somewhere in the bitmap; then
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@ -622,7 +745,11 @@ find_next_usable_block(ext3_grpblk_t start, struct buffer_head *bh,
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return here;
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}
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/*
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/**
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* claim_block()
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* @block: the free block (group relative) to allocate
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* @bh: the bufferhead containts the block group bitmap
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*
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* We think we can allocate this block in this bitmap. Try to set the bit.
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* If that succeeds then check that nobody has allocated and then freed the
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* block since we saw that is was not marked in b_committed_data. If it _was_
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@ -648,7 +775,26 @@ claim_block(spinlock_t *lock, ext3_grpblk_t block, struct buffer_head *bh)
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return ret;
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}
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/*
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/**
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* ext3_try_to_allocate()
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* @sb: superblock
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* @handle: handle to this transaction
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* @group: given allocation block group
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* @bitmap_bh: bufferhead holds the block bitmap
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* @grp_goal: given target block within the group
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* @count: target number of blocks to allocate
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* @my_rsv: reservation window
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*
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* Attempt to allocate blocks within a give range. Set the range of allocation
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* first, then find the first free bit(s) from the bitmap (within the range),
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* and at last, allocate the blocks by claiming the found free bit as allocated.
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*
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* To set the range of this allocation:
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* if there is a reservation window, only try to allocate block(s) from the
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* file's own reservation window;
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* Otherwise, the allocation range starts from the give goal block, ends at
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* the block group's last block.
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*
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* If we failed to allocate the desired block then we may end up crossing to a
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* new bitmap. In that case we must release write access to the old one via
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* ext3_journal_release_buffer(), else we'll run out of credits.
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@ -705,7 +851,8 @@ repeat:
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}
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start = grp_goal;
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if (!claim_block(sb_bgl_lock(EXT3_SB(sb), group), grp_goal, bitmap_bh)) {
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if (!claim_block(sb_bgl_lock(EXT3_SB(sb), group),
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grp_goal, bitmap_bh)) {
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/*
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* The block was allocated by another thread, or it was
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* allocated and then freed by another thread
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@ -720,7 +867,8 @@ repeat:
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grp_goal++;
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while (num < *count && grp_goal < end
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&& ext3_test_allocatable(grp_goal, bitmap_bh)
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&& claim_block(sb_bgl_lock(EXT3_SB(sb), group), grp_goal, bitmap_bh)) {
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&& claim_block(sb_bgl_lock(EXT3_SB(sb), group),
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grp_goal, bitmap_bh)) {
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num++;
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grp_goal++;
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}
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@ -931,9 +1079,10 @@ static int alloc_new_reservation(struct ext3_reserve_window_node *my_rsv,
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if ((my_rsv->rsv_alloc_hit >
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(my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
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/*
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* if we previously allocation hit ration is greater than half
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* we double the size of reservation window next time
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* otherwise keep the same
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* if the previously allocation hit ratio is
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* greater than 1/2, then we double the size of
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* the reservation window the next time,
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* otherwise we keep the same size window
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*/
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size = size * 2;
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if (size > EXT3_MAX_RESERVE_BLOCKS)
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@ -1012,6 +1161,23 @@ retry:
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goto retry;
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}
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/**
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* try_to_extend_reservation()
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* @my_rsv: given reservation window
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* @sb: super block
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* @size: the delta to extend
|
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*
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* Attempt to expand the reservation window large enough to have
|
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* required number of free blocks
|
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*
|
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* Since ext3_try_to_allocate() will always allocate blocks within
|
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* the reservation window range, if the window size is too small,
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* multiple blocks allocation has to stop at the end of the reservation
|
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* window. To make this more efficient, given the total number of
|
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* blocks needed and the current size of the window, we try to
|
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* expand the reservation window size if necessary on a best-effort
|
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* basis before ext3_new_blocks() tries to allocate blocks,
|
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*/
|
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static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
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struct super_block *sb, int size)
|
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{
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|
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@ -1037,7 +1203,17 @@ static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
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spin_unlock(rsv_lock);
|
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}
|
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|
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/*
|
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/**
|
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* ext3_try_to_allocate_with_rsv()
|
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* @sb: superblock
|
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* @handle: handle to this transaction
|
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* @group: given allocation block group
|
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* @bitmap_bh: bufferhead holds the block bitmap
|
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* @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
|
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*
|
||||
* This is the main function used to allocate a new block and its reservation
|
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* window.
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*
|
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|
|
@ -1053,9 +1229,7 @@ static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
|
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* reservation), and there are lots of free blocks, but they are all
|
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* being reserved.
|
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*
|
||||
* 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.
|
||||
*
|
||||
*/
|
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static ext3_grpblk_t
|
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|
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@ -1120,7 +1294,8 @@ ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
|
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*/
|
||||
while (1) {
|
||||
if (rsv_is_empty(&my_rsv->rsv_window) || (ret < 0) ||
|
||||
!goal_in_my_reservation(&my_rsv->rsv_window, grp_goal, group, sb)) {
|
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!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,
|
||||
|
|
@ -1128,19 +1303,22 @@ 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))
|
||||
if ((my_rsv->rsv_start >= group_first_block +
|
||||
EXT3_BLOCKS_PER_GROUP(sb))
|
||||
|| (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;
|
||||
|
|
@ -1165,6 +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;
|
||||
|
|
@ -1179,11 +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)
|
||||
{
|
||||
|
|
@ -1195,13 +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)
|
||||
|
|
@ -1432,7 +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);
|
||||
|
||||
|
|
@ -1475,6 +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;
|
||||
|
|
|
|||
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