Re: ZONE_NORMAL exhaustion (dcache slab)

[Andrew Morton]

Rik van Riel wrote:
> 
> On Mon, 21 Oct 2002, Martin J. Bligh wrote:
> 
> > > Blockdevices only use ZONE_NORMAL for their pagecache.  That cat will
> > > selectively put pressure on the normal zone (and DMA zone, of course).
> >
> > Ah, I recall that now. That's fundamentally screwed.
> 
> It's not too bad since the data can be reclaimed easily.
> 
> The problem in your case is that the dentry and inode cache
> didn't get reclaimed. Maybe there is a leak so they can't get
> reclaimed at all or maybe they just don't get reclaimed fast
> enough.
> 

He had 3 million dentries and only 100k pages on the LRU,
so we should have been reclaiming 60 dentries per scanned
page.

Conceivably the multiply in shrink_slab() overflowed, where
we calculate local variable `delta'.  But doubtful.

First, we need to make it happen again, then see if this (quick
hack) fixes it up.

--- 25/mm/vmscan.c~shrink_slab-overflow	Mon Oct 21 15:40:57 2002
+++ 25-akpm/mm/vmscan.c	Mon Oct 21 15:51:28 2002
@@ -147,14 +147,15 @@ static int shrink_slab(int scanned,  uns
 	list_for_each(lh, &shrinker_list) {
 		struct shrinker *shrinker;
 		int entries;
-		unsigned long delta;
+		long long delta;
 
 		shrinker = list_entry(lh, struct shrinker, list);
 		entries = (*shrinker->shrinker)(0, gfp_mask);
 		if (!entries)
 			continue;
-		delta = scanned * shrinker->seeks * entries;
-		shrinker->nr += delta / (pages + 1);
+		delta = scanned * shrinker->seeks;
+		delta *= entries;
+		shrinker->nr += do_div(delta, pages + 1);
 		if (shrinker->nr > SHRINK_BATCH) {
 			int nr = shrinker->nr;
 

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