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: 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>

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: 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>
Fengguang Wu · Linus Torvalds
1 parent f615bfca46
Showing 2 changed files with 83 additions and 0 deletions Side-by-side Diff
include/linux/fs.h
mm/readahead.c
@@ -695,6 +695,10 @@
  
 /*
  * 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 @@
 	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 */
@@ -711,6 +721,60 @@
 };
 #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 {
 	/*
@@ -592,4 +592,23 @@
 	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);
...	...	@@ -695,6 +695,10 @@
695	695
696	696	/*
697	697	* Track a single file's readahead state
	698	+ *
	699	+ * ================#============\|==================#==================\|
	700	+ * ^ ^ ^ ^
	701	+ * file_ra_state.la_index .ra_index .lookahead_index .readahead_index
698	702	*/
699	703	struct file_ra_state {
700	704	unsigned long start; /* Current window */
...	...	@@ -704,6 +708,12 @@
704	708	unsigned long prev_index; /* Cache last read() position */
705	709	unsigned long ahead_start; /* Ahead window */
706	710	unsigned long ahead_size;
	711	+
	712	+ pgoff_t la_index; /* enqueue time */
	713	+ pgoff_t ra_index; /* begin offset */
	714	+ pgoff_t lookahead_index; /* time to do next readahead */
	715	+ pgoff_t readahead_index; /* end offset */
	716	+
707	717	unsigned long ra_pages; /* Maximum readahead window */
708	718	unsigned long mmap_hit; /* Cache hit stat for mmap accesses */
709	719	unsigned long mmap_miss; /* Cache miss stat for mmap accesses */
...	...	@@ -711,6 +721,60 @@
711	721	};
712	722	#define RA_FLAG_MISS 0x01 /* a cache miss occured against this file */
713	723	#define RA_FLAG_INCACHE 0x02 /* file is already in cache */
	724	+
	725	+/*
	726	+ * Measuring read-ahead sizes.
	727	+ *
	728	+ * \|----------- readahead size ------------>\|
	729	+ * ===#============\|==================#=====================\|
	730	+ * \|------- invoke interval ------>\|-- lookahead size -->\|
	731	+ */
	732	+static inline unsigned long ra_readahead_size(struct file_ra_state *ra)
	733	+{
	734	+ return ra->readahead_index - ra->ra_index;
	735	+}
	736	+
	737	+static inline unsigned long ra_lookahead_size(struct file_ra_state *ra)
	738	+{
	739	+ return ra->readahead_index - ra->lookahead_index;
	740	+}
	741	+
	742	+static inline unsigned long ra_invoke_interval(struct file_ra_state *ra)
	743	+{
	744	+ return ra->lookahead_index - ra->la_index;
	745	+}
	746	+
	747	+/*
	748	+ * Check if @index falls in the readahead windows.
	749	+ */
	750	+static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
	751	+{
	752	+ return (index >= ra->la_index &&
	753	+ index < ra->readahead_index);
	754	+}
	755	+
	756	+/*
	757	+ * Where is the old read-ahead and look-ahead?
	758	+ */
	759	+static inline void ra_set_index(struct file_ra_state *ra,
	760	+ pgoff_t la_index, pgoff_t ra_index)
	761	+{
	762	+ ra->la_index = la_index;
	763	+ ra->ra_index = ra_index;
	764	+}
	765	+
	766	+/*
	767	+ * Where is the new read-ahead and look-ahead?
	768	+ */
	769	+static inline void ra_set_size(struct file_ra_state *ra,
	770	+ unsigned long ra_size, unsigned long la_size)
	771	+{
	772	+ ra->readahead_index = ra->ra_index + ra_size;
	773	+ ra->lookahead_index = ra->ra_index + ra_size - la_size;
	774	+}
	775	+
	776	+unsigned long ra_submit(struct file_ra_state *ra,
	777	+ struct address_space mapping, struct file filp);
714	778
715	779	struct file {
716	780	/*
...	...	@@ -592,4 +592,23 @@
592	592	return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)
593	593	+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
594	594	}
	595	+
	596	+/*
	597	+ * Submit IO for the read-ahead request in file_ra_state.
	598	+ */
	599	+unsigned long ra_submit(struct file_ra_state *ra,
	600	+ struct address_space mapping, struct file filp)
	601	+{
	602	+ unsigned long ra_size;
	603	+ unsigned long la_size;
	604	+ int actual;
	605	+
	606	+ ra_size = ra_readahead_size(ra);
	607	+ la_size = ra_lookahead_size(ra);
	608	+ actual = __do_page_cache_readahead(mapping, filp,
	609	+ ra->ra_index, ra_size, la_size);
	610	+
	611	+ return actual;
	612	+}
	613	+EXPORT_SYMBOL_GPL(ra_submit);