Messages in this thread | | | Date | Tue, 23 Aug 2011 10:00:54 +1000 | From | Dave Chinner <> | Subject | Re: [PATCH 1/2] vmscan: fix initial shrinker size handling |
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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@fromorbit.com> 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....
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....
So, grotty code but I don't think there is even a problem that can be tripped right now.
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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