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readahead: data structure and routines

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

Signed-off-by: Fengguang 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Fengguang Wu 2007-07-19 01:47:59 -07:00 committed by Linus Torvalds
parent f615bfca46
commit 5ce1110b92
2 changed files with 83 additions and 0 deletions
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64
include/linux/fs.h
View file

@ -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

19
mm/readahead.c
View file

@ -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);