[PATCH 3/9] readahead: MIN_RA_PAGES/MAX_RA_PAGES macros

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

[-- Attachment #1: readahead-minmax_ra_pages.patch --]
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Define two convenient macros for read-ahead:
	- MAX_RA_PAGES: rounded down counterpart of VM_MAX_READAHEAD
	- MIN_RA_PAGES: rounded _up_ counterpart of VM_MIN_READAHEAD

Note that the rounded up MIN_RA_PAGES will work flawlessly with _large_
page sizes like 64k.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

 mm/readahead.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- linux-2.6.22-rc1-mm1.orig/mm/readahead.c
+++ linux-2.6.22-rc1-mm1/mm/readahead.c
@@ -21,8 +21,16 @@ void default_unplug_io_fn(struct backing
 }
 EXPORT_SYMBOL(default_unplug_io_fn);
 
+/*
+ * Convienent macros for min/max read-ahead pages.
+ * Note that MAX_RA_PAGES is rounded down, while MIN_RA_PAGES is rounded up.
+ * The latter is necessary for systems with large page size(i.e. 64k).
+ */
+#define MAX_RA_PAGES	(VM_MAX_READAHEAD*1024 / PAGE_CACHE_SIZE)
+#define MIN_RA_PAGES	DIV_ROUND_UP(VM_MIN_READAHEAD*1024, PAGE_CACHE_SIZE)
+
 struct backing_dev_info default_backing_dev_info = {
-	.ra_pages	= (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE,
+	.ra_pages	= MAX_RA_PAGES,
 	.state		= 0,
 	.capabilities	= BDI_CAP_MAP_COPY,
 	.unplug_io_fn	= default_unplug_io_fn,
@@ -51,7 +59,7 @@ static inline unsigned long get_max_read
 
 static inline unsigned long get_min_readahead(struct file_ra_state *ra)
 {
-	return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	return MIN_RA_PAGES;
 }
 
 static inline void reset_ahead_window(struct file_ra_state *ra)

--