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Commit e35fd660 authored by Theodore Ts'o's avatar Theodore Ts'o
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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: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 8e48dcfb

fs/ext4/ext4.h

+27 −3
Original line number Diff line number Diff line
@@ -125,6 +125,29 @@ struct ext4_allocation_request { 
	unsigned int flags;

};



/*

 * Logical to physical block mapping, used by ext4_map_blocks()

 *

 * This structure is used to pass requests into ext4_map_blocks() as

 * well as to store the information returned by ext4_map_blocks().  It

 * takes less room on the stack than a struct buffer_head.

 */

#define EXT4_MAP_NEW		(1 << BH_New)

#define EXT4_MAP_MAPPED		(1 << BH_Mapped)

#define EXT4_MAP_UNWRITTEN	(1 << BH_Unwritten)

#define EXT4_MAP_BOUNDARY	(1 << BH_Boundary)

#define EXT4_MAP_UNINIT		(1 << BH_Uninit)

#define EXT4_MAP_FLAGS		(EXT4_MAP_NEW | EXT4_MAP_MAPPED |\

				 EXT4_MAP_UNWRITTEN | EXT4_MAP_BOUNDARY |\

				 EXT4_MAP_UNINIT)



struct ext4_map_blocks {

	ext4_fsblk_t m_pblk;

	ext4_lblk_t m_lblk;

	unsigned int m_len;

	unsigned int m_flags;

};



/*

 * For delayed allocation tracking

 */
@@ -1773,9 +1796,8 @@ extern int ext4_ext_tree_init(handle_t *handle, struct inode *); 
extern int ext4_ext_writepage_trans_blocks(struct inode *, int);

extern int ext4_ext_index_trans_blocks(struct inode *inode, int nrblocks,

				       int chunk);

extern int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,

			       ext4_lblk_t iblock, unsigned int max_blocks,

			       struct buffer_head *bh_result, int flags);

extern int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,

			       struct ext4_map_blocks *map, int flags);

extern void ext4_ext_truncate(struct inode *);

extern void ext4_ext_init(struct super_block *);

extern void ext4_ext_release(struct super_block *);
@@ -1783,6 +1805,8 @@ extern long ext4_fallocate(struct inode *inode, int mode, loff_t offset, 
			  loff_t len);

extern int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,

			  ssize_t len);

extern int ext4_map_blocks(handle_t *handle, struct inode *inode,

			   struct ext4_map_blocks *map, int flags);

extern int ext4_get_blocks(handle_t *handle, struct inode *inode,

			   sector_t block, unsigned int max_blocks,

			   struct buffer_head *bh, int flags);

fs/ext4/extents.c

+114 −123

File changed.

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fs/ext4/inode.c

+58 −44

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