On 6/29/18 8:15 PM, Andrew Morton wrote:
On Fri, 29 Jun 2018 19:28:15 -0700 Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote:
Well, those unaddressed usecases will need to be fixed at some point.
we're adding a bunch of code to 32-bit kernels which will never beI agree it is not that perfect. But, it still could improve the most use
I'm thinking it would be better to be much more explicit with "#ifdef
CONFIG_64BIT" in this code, rather than relying upon the above magic.
But I tend to think that the fact that we haven't solved anything on
locked vmas or on uprobed mappings is a shostopper for the whole
What's our plan for that?
As I mentioned in the earlier email, locked and hugetlb cases might be able to be solved by separating vm_flags update and actual unmap. I will look into it further later.
From my point of view, uprobe mapping sounds not that vital.
Would one of your earlier designs have addressed all usecases? I
expect the dumb unmap-a-little-bit-at-a-time approach would have?
Yes. The v1 design does unmap with holding write map_sem. So, the vm_flags update is not a problem.
For the locked vmas and hugetlb vmas, unmapping operations need modify
vm_flags. But, I'm wondering we might be able to separate unmap and
vm_flags update. Because we know they will be unmapped right away, the
vm_flags might be able to be updated in write mmap_sem critical section
before the actual unmap is called or after it. This is just off the top
of my head.
For uprobed mappings, I'm not sure how vital it is to this case.