On Wed, 5 Oct 2011 23:52:05 +0200 Johannes Weiner <jweiner@xxxxxxxxxx> wrote: > On Tue, Sep 13, 2011 at 08:38:36PM +0200, Johannes Weiner wrote: > > On Tue, Aug 23, 2011 at 10:00:54AM +1000, Dave Chinner wrote: > > > On Mon, Aug 22, 2011 at 04:38:21PM -0700, Andrew Morton wrote: > > > > On Tue, 23 Aug 2011 09:22:57 +1000 > > > > Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > > > > > > On Mon, Aug 22, 2011 at 02:17:21PM +0300, Konstantin Khlebnikov wrote: > > > > > > Shrinker function can returns -1, it means it cannot do anything without a risk of deadlock. > > > > > > For example prune_super() do this if it cannot grab superblock refrence, even if nr_to_scan=0. > > > > > > Currenly we interpret this like ULONG_MAX size shrinker, evaluate total_scan according this, > > > > > > and next time this shrinker can get really big pressure. Let's skip such shrinkers instead. > > > > > > > > > > > > Also make total_scan signed, otherwise check (total_scan < 0) below never works. > > > > > > > > > > I've got a patch set I am going to post out today that makes this > > > > > irrelevant. > > > > > > > > Well, how serious is the bug? If it's a non-issue then we can leave > > > > the fix until 3.1. If it's a non-non-issue then we'd need a minimal > > > > patch to fix up 3.1 and 3.0.x. > > > > > > I'm pretty sure it's a non-issue. I'm pretty sure all of the > > > shrinkers return a count >= 0 rather than -1 when passed nr_to_scan > > > == 0 (i.e. they skip the GFP_NOFS checking), so getting a max_pass > > > of -1 isn't going to happen very often.... > > > > Except for the case which Konstantin laid out, grabbing the super > > block reference. How likely is that? And why isn't once enough to > > build up quite a high number? > > > > > And with total_scan being unsigned, the negative check is followed > > > by a "if (total_scan > max_pass * 2)" check, which will catch > > > numbers that would have gone negative anyway because max_pass won't > > > be negative.... > > > > total_scan = nr; > > max_pass = do_shrinker_shrink(shrinker, shrink, 0); > > delta = (4 * nr_pages_scanned) / shrinker->seeks; > > delta *= max_pass; > > do_div(delta, lru_pages + 1); > > total_scan += delta; > > > > max_pass, an unsigned long, is what the shrinker returned, so > > ULONG_MAX. ULONG_MAX * 2 is ULONG_MAX - 1, still pretty big? > > > > Even for high values of delta (lots of pages scanned, few lru pages > > left), it won't come nowhere near max_pass such that the product of > > the two is a reasonable number again. > > Ping? I have a note against that patch that David was working on some alternative. So ... ping, indeed. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>