[PATCH] 3/4: writeout watermarks

[Nick Piggin <nickpiggin@yahoo.com.au>]

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3/4

3rd attempt for this patch ;)
I have since addressed your concerns.

So for example, with a 10/40 async/sync ratio, if the sync
watermark is moved down to 20, the async mark will be moved
to 5, preserving the ratio.

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Slightly change the writeout watermark calculations so we keep background
and synchronous writeout watermarks in the same ratios after adjusting them.
This ensures we should always attempt to start background writeout before
synchronous writeout.

Signed-off-by: Nick Piggin <nickpiggin@cyberone.com.au>


---

 linux-2.6-npiggin/mm/page-writeback.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff -puN mm/page-writeback.c~vm-tune-writeout mm/page-writeback.c
--- linux-2.6/mm/page-writeback.c~vm-tune-writeout	2004-08-06 14:48:45.000000000 +1000
+++ linux-2.6-npiggin/mm/page-writeback.c	2004-08-06 14:48:45.000000000 +1000
@@ -153,9 +153,11 @@ get_dirty_limits(struct writeback_state 
 	if (dirty_ratio < 5)
 		dirty_ratio = 5;
 
-	background_ratio = dirty_background_ratio;
-	if (background_ratio >= dirty_ratio)
-		background_ratio = dirty_ratio / 2;
+	/*
+	 * Keep the ratio between dirty_ratio and background_ratio roughly
+	 * what the sysctls are after dirty_ratio has been scaled (above).
+	 */
+	background_ratio = dirty_background_ratio * dirty_ratio/vm_dirty_ratio;
 
 	background = (background_ratio * total_pages) / 100;
 	dirty = (dirty_ratio * total_pages) / 100;

_