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Subject[PATCH 09/33] readahead: {MIN,MAX}_RA_PAGES
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: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
mm/readahead.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
--- linux-2.6.17-rc4-mm3.orig/mm/readahead.c
+++ linux-2.6.17-rc4-mm3/mm/readahead.c
@@ -17,13 +17,21 @@
#include <linux/backing-dev.h>
#include <linux/pagevec.h>

+/*
+ * 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)
+
void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
}
EXPORT_SYMBOL(default_unplug_io_fn);

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,
@@ -52,7 +60,7 @@ 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)
--
-
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