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Commit 5ce1110b authored by Fengguang Wu's avatar Fengguang Wu Committed by Linus Torvalds
Browse files

readahead: data structure and routines 



Extend struct file_ra_state to support the on-demand readahead logic.  Also
define some helpers for it.

Signed-off-by: default avatarFengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f615bfca

include/linux/fs.h

+64 −0
Original line number Diff line number Diff line
@@ -695,6 +695,10 @@ struct fown_struct { 


/*

 * Track a single file's readahead state

 *

 *  ================#============|==================#==================|

 *                  ^            ^                  ^                  ^

 *  file_ra_state.la_index    .ra_index   .lookahead_index   .readahead_index

 */

struct file_ra_state {

	unsigned long start;		/* Current window */
@@ -704,6 +708,12 @@ struct file_ra_state { 
	unsigned long prev_index;	/* Cache last read() position */

	unsigned long ahead_start;	/* Ahead window */

	unsigned long ahead_size;



	pgoff_t la_index;               /* enqueue time */

	pgoff_t ra_index;               /* begin offset */

	pgoff_t lookahead_index;        /* time to do next readahead */

	pgoff_t readahead_index;        /* end offset */



	unsigned long ra_pages;		/* Maximum readahead window */

	unsigned long mmap_hit;		/* Cache hit stat for mmap accesses */

	unsigned long mmap_miss;	/* Cache miss stat for mmap accesses */
@@ -712,6 +722,60 @@ struct file_ra_state { 
#define RA_FLAG_MISS 0x01	/* a cache miss occured against this file */

#define RA_FLAG_INCACHE 0x02	/* file is already in cache */



/*

 * Measuring read-ahead sizes.

 *

 *                  |----------- readahead size ------------>|

 *  ===#============|==================#=====================|

 *     |------- invoke interval ------>|-- lookahead size -->|

 */

static inline unsigned long ra_readahead_size(struct file_ra_state *ra)

{

	return ra->readahead_index - ra->ra_index;

}



static inline unsigned long ra_lookahead_size(struct file_ra_state *ra)

{

	return ra->readahead_index - ra->lookahead_index;

}



static inline unsigned long ra_invoke_interval(struct file_ra_state *ra)

{

	return ra->lookahead_index - ra->la_index;

}



/*

 * Check if @index falls in the readahead windows.

 */

static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)

{

	return (index >= ra->la_index &&

		index <  ra->readahead_index);

}



/*

 * Where is the old read-ahead and look-ahead?

 */

static inline void ra_set_index(struct file_ra_state *ra,

				pgoff_t la_index, pgoff_t ra_index)

{

	ra->la_index = la_index;

	ra->ra_index = ra_index;

}



/*

 * Where is the new read-ahead and look-ahead?

 */

static inline void ra_set_size(struct file_ra_state *ra,

				unsigned long ra_size, unsigned long la_size)

{

	ra->readahead_index = ra->ra_index + ra_size;

	ra->lookahead_index = ra->ra_index + ra_size - la_size;

}



unsigned long ra_submit(struct file_ra_state *ra,

		       struct address_space *mapping, struct file *filp);



struct file {

	/*

	 * fu_list becomes invalid after file_free is called and queued via

mm/readahead.c

+19 −0
Original line number Diff line number Diff line
@@ -592,3 +592,22 @@ unsigned long max_sane_readahead(unsigned long nr) 
	return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)

		+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);

}



/*

 * Submit IO for the read-ahead request in file_ra_state.

 */

unsigned long ra_submit(struct file_ra_state *ra,

		       struct address_space *mapping, struct file *filp)

{

	unsigned long ra_size;

	unsigned long la_size;

	int actual;



	ra_size = ra_readahead_size(ra);

	la_size = ra_lookahead_size(ra);

	actual = __do_page_cache_readahead(mapping, filp,

					ra->ra_index, ra_size, la_size);



	return actual;

}

EXPORT_SYMBOL_GPL(ra_submit);