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 <[email protected]>
---
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)
--