Re: Page cache write performance issue

[Andrew Morton <akpm@xxxxxxxx>]

Nathan Scott <nathans@xxxxxxx> wrote:
>
>  So, any ideas what happened to 2.6.9?

Does reverting the below fix it up?

>   Whats the rationale for commencing writeout earlier in 2.6
> (even when there's
>  so much free memory available)?

There wasn't much rationale behind that patch - that's why I dropped it the
first three times ;)  I have no problem with making it four times.

It could be that small values of unmapped_ratio are making background_ratio
too small.


--- a/mm/page-writeback.c       10 Aug 2004 04:16:17 -0000      1.43
+++ a/mm/page-writeback.c       13 Oct 2004 06:12:03 -0000
@@ -153,9 +153,11 @@
        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;