linux-kernel - Re: [PATCH 1/3] x86,mm/pat: Use generic interval trees

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Message-ID: <20190822181701.zhfdkjbwjh56i3ax@linux-r8p5>
Date:   Thu, 22 Aug 2019 11:17:01 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Michel Lespinasse <walken@...gle.com>
Cc:     mingo@...nel.org, tglx@...utronix.de, peterz@...radead.org,
        akpm@...ux-foundation.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/3] x86,mm/pat: Use generic interval trees

>On Wed, 21 Aug 2019, Michel Lespinasse wrote:
>>As I had commented some time ago, I wish the interval trees used [start,end)
>>intervals instead of [start,last] - it would be a better fit for basically
>>all of the current interval tree users.

So the vma_interval_tree (which is a pretty important user) tends to break this
pattern, as most lookups are [a,a]. We would have to update most of the
vma_interval_tree_foreach calls, for example, to now do [a,a+1[ such that we
don't break things. Some cases for the anon_vma_tree as well (ie memory-failure).

I'm not sure anymore it's worth going down this path as we end up exchanging one
hack for another (and the vma_interval_tree is a pretty big user); but I'm sure
you're aware of this and thus disagree.

Thanks,
Davidlohr