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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Michel Lespinasse <walken@google.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org
Subject: Re: [PATCH -next 00/11] lib/interval-tree: move to half closed intervals
Date: Fri, 4 Oct 2019 14:45:15 -0300	[thread overview]
Message-ID: <20191004174515.GE13988@ziepe.ca> (raw)
In-Reply-To: <CANN689G3chM1FjFPdCNm9_OQxazs7YP1PuZLpqGtq=qzaZ0Hbw@mail.gmail.com>

On Fri, Oct 04, 2019 at 06:15:11AM -0700, Michel Lespinasse wrote:
> Hi Jason,
> 
> On Thu, Oct 3, 2019 at 5:26 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > Hurm, this is not entirely accurate. Most users do actually want
> > overlapping and multiple ranges. I just studied this extensively:
> 
> (Just curious, are you the person we discussed this with after the
> Maple Tree talk at LPC 2019 ?)

Possibly!
 
> I think we have two separate API problems there:
> - overlapping vs non-overlapping intervals (the interval tree API
> supports overlapping intervals, but some users are confused about
> this)

I think we just have a bunch of confused drivers, ie the two drm
drivers sure look confused to me.

> - closed vs half-open interval definitions

I'm not sure why this is a big problem..

We may actually just have bugs in handling the '-1' as it is supposed
to be written as start + (size-1) so that start + size == ULONG_MAX+1
works properly.

> > hfi1/mmu_rb definitely needs overlapping as it is dealing with
> > userspace VA ranges under control of userspace. As do the other
> > infiniband users.
> 
> Do you have a handle on what usnic is doing with its intervals ?
> usnic_uiom_insert_interval() has some complicated logic to avoid
> having overlapping intervals, which is very confusing to me.

I don't know why it is so complicated, but I can say that it is
storing userspace VA's in that tree.

I have some feeling this driver is trying to use the IOMMU to create a
mirror of the userspace VA

Userspace can request the HW be able to access any set of overlapping
regions and so the driver must intersect all the ranges and compute a
list of VA pages to IOMMU map. Just guessing.

Jason


      parent reply	other threads:[~2019-10-04 17:45 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03 20:18 [PATCH -next 00/11] lib/interval-tree: move to half closed intervals Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 01/11] mm: introduce vma_interval_tree_foreach_stab() Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 02/11] lib/interval-tree: add an equivalent tree with [a,b) intervals Davidlohr Bueso
2019-10-04 11:02   ` Michel Lespinasse
2019-10-03 20:18 ` [PATCH 03/11] drm/amdgpu: convert amdgpu_vm_it to half closed intervals Davidlohr Bueso
2019-10-04  6:54   ` Koenig, Christian
2019-10-04 11:36     ` Michel Lespinasse
2019-10-04 12:39       ` Christian König
2019-10-03 20:18 ` [PATCH 04/11] drm: convert drm_mm_interval_tree " Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 05/11] IB/hfi1: convert __mmu_int_rb " Davidlohr Bueso
2019-10-04 11:50   ` Michel Lespinasse
2019-10-04 19:41     ` Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 06/11] IB,usnic: convert usnic_uiom_interval_tree " Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 07/11] vhost: convert vhost_umem_interval_tree " Davidlohr Bueso
2019-10-04 12:10   ` Michel Lespinasse
2019-10-04 19:44     ` Davidlohr Bueso
2019-10-10  5:49   ` Jason Wang
2019-10-03 20:18 ` [PATCH 08/11] mm: convert vma_interval_tree " Davidlohr Bueso
2019-10-03 20:41   ` Matthew Wilcox
2019-10-04 12:30   ` Michel Lespinasse
2019-10-03 20:18 ` [PATCH 09/11] lib/interval-tree: convert interval_tree " Davidlohr Bueso
2019-10-03 22:50   ` kbuild test robot
2019-10-04  6:57   ` Koenig, Christian
2019-10-04  7:20     ` Koenig, Christian
2019-10-08 16:59       ` Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 10/11] lib: drop interval_tree_generic.h Davidlohr Bueso
2019-10-03 20:18 ` [PATCH 11/11] x86/mm, pat: convert pat tree to generic interval tree Davidlohr Bueso
2019-10-07 15:33   ` Ingo Molnar
2019-10-21 23:24     ` Davidlohr Bueso
2019-10-03 20:32 ` [PATCH -next 00/11] lib/interval-tree: move to half closed intervals Matthew Wilcox
2019-10-03 21:10   ` Davidlohr Bueso
2019-10-04 12:43   ` Michel Lespinasse
2019-10-04  0:26 ` Jason Gunthorpe
2019-10-04  2:48   ` Davidlohr Bueso
2019-10-04 13:15   ` Michel Lespinasse
2019-10-04 16:03     ` Matthew Wilcox
2019-10-04 19:35       ` Davidlohr Bueso
2019-10-04 17:45     ` Jason Gunthorpe [this message]

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