On 13/10/2017 19:17, Michal Hocko wrote:
On Fri 13-10-17 10:56:13, Cristopher Lameter wrote:
On Fri, 13 Oct 2017, Michal Hocko wrote:
There is a generic posix interface that could we used for a variety of
specific hardware dependent use cases.
Yes you wrote that already and my counter argument was that this generic
posix interface shouldn't bypass virtual memory abstraction.
It does do that? In what way?
availability of the virtual address space depends on the availability of
the same sized contiguous physical memory range. That sounds like the
abstraction is gone to large part to me.
In what way? userspace users will still be working with virtual memory.
There are numerous RDMA devices that would all need the mmap
implementation. And this covers only the needs of one subsystem. There are
other use cases.
That doesn't prevent providing a library function which could be reused
by all those drivers. Nothing really too much different from
remap_pfn_range.
And then in all the other use cases as well. It would be much easier if
mmap could give you the memory you need instead of havig numerous drivers
improvise on their own. This is in particular also useful
for numerous embedded use cases where you need contiguous memory.
But a generic implementation would have to deal with many issues as
already mentioned. If you make this driver specific you can have access
control based on fd etc... I really fail to see how this is any
different from remap_pfn_range.
Why have several driver specific implementation if you can generalize
the idea and implement
an already existing POSIX standard?
--
Guy
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