Re: [patch] real-time enhanced page allocator and throttling

[Andrew Morton <akpm@osdl.org>]

Robert Love <rml@tech9.net> wrote:
>
> > There is a very good argument for giving !SCHED_OTHER tasks
>  > "special treatment" in the VM.
> 
>  Yes, there is.
> 
>  Attached patch is against 2.6.0-test2-mm4. 

Thanks.  I guess we should extend the special treatment in the page
allocator and in balance_dirty_pages() we still should go and update the
various bits of state and poke pdflush if needed.

These changes should yield quite significant improvements in worst-case
latencies for realtime tasks under some situations.  I'll test them...


diff -puN mm/page_alloc.c~rt-tasks-special-vm-treatment-2 mm/page_alloc.c
--- 25/mm/page_alloc.c~rt-tasks-special-vm-treatment-2	2003-08-05 16:57:51.000000000 -0700
+++ 25-akpm/mm/page_alloc.c	2003-08-05 16:58:11.000000000 -0700
@@ -592,6 +592,8 @@ __alloc_pages(unsigned int gfp_mask, uns
 		local_min = z->pages_min;
 		if (gfp_mask & __GFP_HIGH)
 			local_min >>= 2;
+		if (rt_task(p))
+			local_min >>= 1;
 		min += local_min;
 		if (z->free_pages >= min ||
 				(!wait && z->free_pages >= z->pages_high)) {
diff -puN mm/page-writeback.c~rt-tasks-special-vm-treatment-2 mm/page-writeback.c
--- 25/mm/page-writeback.c~rt-tasks-special-vm-treatment-2	2003-08-05 16:57:51.000000000 -0700
+++ 25-akpm/mm/page-writeback.c	2003-08-05 17:02:40.000000000 -0700
@@ -144,7 +144,7 @@ get_dirty_limits(struct page_state *ps, 
  * If we're over `background_thresh' then pdflush is woken to perform some
  * writeout.
  */
-void balance_dirty_pages(struct address_space *mapping)
+static void balance_dirty_pages(struct address_space *mapping)
 {
 	struct page_state ps;
 	long nr_reclaimable;
@@ -167,8 +167,9 @@ void balance_dirty_pages(struct address_
 		nr_reclaimable = ps.nr_dirty + ps.nr_unstable;
 		if (nr_reclaimable + ps.nr_writeback <= dirty_thresh)
 			break;
-
 		dirty_exceeded = 1;
+		if (rt_task(current))
+			break;
 
 		/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
 		 * Unstable writes are a feature of certain networked
@@ -223,7 +224,7 @@ void balance_dirty_pages_ratelimited(str
 	 * Check the rate limiting. Also, we do not want to throttle real-time
 	 * tasks in balance_dirty_pages(). Period.
 	 */
-	if (get_cpu_var(ratelimits)++ >= ratelimit && !rt_task(current)) {
+	if (get_cpu_var(ratelimits)++ >= ratelimit) {
 		__get_cpu_var(ratelimits) = 0;
 		put_cpu_var(ratelimits);
 		balance_dirty_pages(mapping);

_

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>