Re: [patch] adjustments to dirty memory thresholds

[Andrew Morton]

Andrew Morton wrote:
> 
> ...
> Well it's presumably the GFP_NOIO which has killed it - we can't wait
> on PG_writeback pages and we can't write out dirty pages.  Taking a
> nap in mempool_alloc is appropriate.

Actually, it might be better to teach mempool_alloc to not call page reclaim
at all if __GFP_FS is not set.  Just kick bdflush and go to sleep.

I really, really, really dislike the VM's tendency to go and scan hundreds
of thousands of pages.  It's a clear sign of an inappropriate algorithm.

Test something like this, please?

--- 2.5.32/mm/mempool.c~wli	Wed Aug 28 15:07:31 2002
+++ 2.5.32-akpm/mm/mempool.c	Wed Aug 28 15:12:53 2002
@@ -196,10 +196,11 @@ repeat_alloc:
 		return element;
 
 	/*
-	 * If the pool is less than 50% full then try harder
-	 * to allocate an element:
+	 * If the pool is less than 50% full and we can perform effective
+	 * page reclaim then try harder to allocate an element:
 	 */
-	if ((gfp_mask != gfp_nowait) && (pool->curr_nr <= pool->min_nr/2)) {
+	if ((gfp_mask & __GFP_FS) && (gfp_mask != gfp_nowait) &&
+			(pool->curr_nr <= pool->min_nr/2)) {
 		element = pool->alloc(gfp_mask, pool->pool_data);
 		if (likely(element != NULL))
 			return element;

.