Messages in this thread Patch in this message | | | Date | Sat, 19 Mar 2011 15:52:57 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: remap_file_pages doesn't like MAP_ANONYMOUS (but used to?) |
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On Wed, 16 Mar 2011, Kenny Simpson wrote: > Hello, > In older kernels (2.6.15-2.6.18?) I was able to make an anonymous mapping and remap part of it back over itself to create a circular buffer: > p = mmap(0, sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0) > remap_file_pages(p + sz/2, sz/2, 0/*prot*/, 0/*offset*/, 0/*flags*/) > > I find the same method fails with EINVAL on the remap_file_pages call in 2.6.35/38. Making a dummy file or shared memory object works, but seems a bit more messy. > > Why drop support for ANONYMOUS? Is there another way to get the same effect?
Thanks for reporting. It was a simple oversight: and until you came along, nobody noticed. Here's the patch, I'll pass it upstream shortly.
[PATCH] shmem: let shared anonymous be nonlinear again
Up to 2.6.22, you could use remap_file_pages(2) on a tmpfs file or a shared mapping of /dev/zero or a shared anonymous mapping. In 2.6.23 we disabled it by default, but set VM_CAN_NONLINEAR to enable it on safe mappings. We made sure to set it in shmem_mmap() for tmpfs files, but missed it in shmem_zero_setup() for the others. Fix that at last.
Reported-by: Kenny Simpson <theonetruekenny@yahoo.com> Signed-off-by: Hugh Dickins <hughd@google.com> ---
mm/shmem.c | 1 + 1 file changed, 1 insertion(+)
--- 2.6.38/mm/shmem.c 2011-03-14 18:20:32.000000000 -0700 +++ linux/mm/shmem.c 2011-03-19 15:09:26.000000000 -0700 @@ -2791,5 +2791,6 @@ int shmem_zero_setup(struct vm_area_stru fput(vma->vm_file); vma->vm_file = file; vma->vm_ops = &shmem_vm_ops; + vma->vm_flags |= VM_CAN_NONLINEAR; return 0; } | |