lkml.org 
[lkml]   [2020]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RESEND PATCH 2/3] nouveau: fix mixed normal and device private page migration
On Thu, Jun 25, 2020 at 10:25:38AM -0700, Ralph Campbell wrote:
> Making sure to include linux-mm and Bharata B Rao for IBM's
> use of migrate_vma*().
>
> On 6/24/20 11:10 AM, Ralph Campbell wrote:
> >
> > On 6/24/20 12:23 AM, Christoph Hellwig wrote:
> > > On Mon, Jun 22, 2020 at 04:38:53PM -0700, Ralph Campbell wrote:
> > > > The OpenCL function clEnqueueSVMMigrateMem(), without any flags, will
> > > > migrate memory in the given address range to device private memory. The
> > > > source pages might already have been migrated to device private memory.
> > > > In that case, the source struct page is not checked to see if it is
> > > > a device private page and incorrectly computes the GPU's physical
> > > > address of local memory leading to data corruption.
> > > > Fix this by checking the source struct page and computing the correct
> > > > physical address.
> > >
> > > I'm really worried about all this delicate code to fix the mixed
> > > ranges.  Can't we make it clear at the migrate_vma_* level if we want
> > > to migrate from or two device private memory, and then skip all the work
> > > for regions of memory that already are in the right place?  This might be
> > > a little more work initially, but I think it leads to a much better
> > > API.
> > >
> >
> > The current code does encode the direction with src_owner != NULL meaning
> > device private to system memory and src_owner == NULL meaning system
> > memory to device private memory. This patch would obviously defeat that
> > so perhaps a flag could be added to the struct migrate_vma to indicate the
> > direction but I'm unclear how that makes things less delicate.
> > Can you expand on what you are worried about?
> >
> > The issue with invalidations might be better addressed by letting the device
> > driver handle device private page TLB invalidations when migrating to
> > system memory and changing migrate_vma_setup() to only invalidate CPU
> > TLB entries for normal pages being migrated to device private memory.
> > If a page isn't migrating, it seems inefficient to invalidate those TLB
> > entries.
> >
> > Any other suggestions?
>
> After a night's sleep, I think this might work. What do others think?
>
> 1) Add a new MMU_NOTIFY_MIGRATE enum to mmu_notifier_event.
>
> 2) Change migrate_vma_collect() to use the new MMU_NOTIFY_MIGRATE event type.
>
> 3) Modify nouveau_svmm_invalidate_range_start() to simply return (no invalidations)
> for MMU_NOTIFY_MIGRATE mmu notifier callbacks.

Isn't it a bit of an assumption that migrate_vma_collect() is only
used by nouveau itself?

What if some other devices' device_private pages are being migrated?

Jason

\
 
 \ /
  Last update: 2020-06-25 19:32    [W:0.436 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site