Am 25.03.21 um 13:42 schrieb Jason Gunthorpe:
On Thu, Mar 25, 2021 at 01:09:14PM +0100, Christian König wrote:
Am 25.03.21 um 13:01 schrieb Jason Gunthorpe:
On Thu, Mar 25, 2021 at 12:53:15PM +0100, Thomas Hellström (Intel) wrote:
Nope. The point here was that in this case, to make sure mmap uses the
correct VA to give us a reasonable chance of alignement, the driver might
need to be aware of and do trickery with the huge page-table-entry sizes
anyway, although I think in most cases a standard helper for this can be
supplied.
Of course the driver needs some way to influence the VA mmap uses,
gernally it should align to the natural page size of the device
Well a mmap() needs to be aligned to the page size of the CPU, but not
necessarily to the one of the device.
So I'm pretty sure the device driver should not be involved in any way the
choosing of the VA for the CPU mapping.
No, if the device wants to use huge pages it must influence the mmap
VA or it can't form huge pgaes.
No, that's the job of the core MM and not of the individual driver.
In other words current->mm->get_unmapped_area should already return a
properly aligned VA.
Messing with that inside file->f_op->get_unmapped_area is utterly
nonsense as far as I can see.
It happens to be this way currently, but that is not even remotely good
design.
Christian.
It is the same reason why mmap returns 2M stuff these days to make THP
possible
Jason
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