Re: [PATCH] remove throttle_vm_writeout()

[Peter Zijlstra]

On Fri, 2007-10-05 at 11:22 +0200, Miklos Szeredi wrote:
> > So how do we end up with more writeback pages than that? should we teach
> > pdflush about these limits as well?
> 
> Ugh.
> 
> I think we should rather fix vmscan to not spin when all pages of a
> zone are already under writeout.  Which is the _real_ problem,
> according to Andrew.



diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 4ef4d22..eff2438 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -88,7 +88,7 @@ static inline void wait_on_inode(struct inode *inode)
 int wakeup_pdflush(long nr_pages);
 void laptop_io_completion(void);
 void laptop_sync_completion(void);
-void throttle_vm_writeout(gfp_t gfp_mask);
+void throttle_vm_writeout(struct zone *zone, gfp_t gfp_mask);
 
 /* These are exported to sysctl. */
 extern int dirty_background_ratio;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eec1481..f949997 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -326,11 +326,8 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 }
 EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
 
-void throttle_vm_writeout(gfp_t gfp_mask)
+void throttle_vm_writeout(struct zone *zone, gfp_t gfp_mask)
 {
-	long background_thresh;
-	long dirty_thresh;
-
 	if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO)) {
 		/*
 		 * The caller might hold locks which can prevent IO completion
@@ -342,17 +339,16 @@ void throttle_vm_writeout(gfp_t gfp_mask)
 	}
 
         for ( ; ; ) {
-		get_dirty_limits(&background_thresh, &dirty_thresh, NULL);
+		unsigned long thresh = zone_page_state(zone, NR_ACTIVE) +
+			zone_page_state(zone, NR_INACTIVE);
 
-                /*
-                 * Boost the allowable dirty threshold a bit for page
-                 * allocators so they don't get DoS'ed by heavy writers
-                 */
-                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
+		/*
+		 * wait when 75% of the zone's pages are under writeback
+		 */
+		thresh -= thresh >> 2;
+		if (zone_page_state(zone, NR_WRITEBACK) < thresh)
+			break;
 
-                if (global_page_state(NR_UNSTABLE_NFS) +
-			global_page_state(NR_WRITEBACK) <= dirty_thresh)
-                        	break;
                 congestion_wait(WRITE, HZ/10);
         }
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1be5a63..7dd6bd9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -948,7 +948,7 @@ static unsigned long shrink_zone(int priority, struct zone *zone,
 		}
 	}
 
-	throttle_vm_writeout(sc->gfp_mask);
+	throttle_vm_writeout(zone, sc->gfp_mask);
 
 	atomic_dec(&zone->reclaim_in_progress);
 	return nr_reclaimed;

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