Messages in this thread | | | Date | Thu, 29 Jan 2009 20:49:52 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments |
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On Thu, 29 Jan 2009, Lee Schermerhorn wrote: > > Just want to note that install_special_mappings()--used for, e.g., the > vdso--sets VM_DONTEXPAND [one of the VM_SPECIAL flags] which, if we want > to prevent merging, makes a lot of sense to me.
Yes. VM_DONTEXPAND in many ways really fits the "don't merge" thing, because the whole mremap() VM expansion thing is really equivalent to this explicit merge.
> It appears that get_user_pages() will balk at addresses in vmas with > VM_IO [and VM_PFNMAP] which might not be what one wants. For example, > you can't pre-populate the ptes via make_pages_present() with this flag.
Well, anybody who plays games with vm_pgoff really _should_ be VM_IO. I don't see any real reason for it except for having a very special IO mapping. Of course, you quite possibly _also_ want VM_DONTEXPAND.
Linus
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