Re: [Discontig-devel] Re: [Linux-ia64] Re: 2.5.59 & mmap_sem

[Andrew Morton <akpm@digeo.com>]

William Lee Irwin III <wli@holomorphy.com> wrote:
>
> On Tue, Feb 18, 2003 at 09:46:31AM +0100, Xavier Bru wrote:
> > Thanks for your answers.
> > You are right, we do not need a page structure for mapping /dev/mem in 
> > IO space (I am not a mm expert :-).
> > Here after a possible patch that allows the Xserver running on the NUMA
> > platform. (We had the same problem on Azusa).
> 
> Looks perfectly reasonable to me. Other discontig/NUMA implementations
> are likely to run into the same issue.
> 
> You might want to send this on to lkml and cc: akpm, he's pretty much
> the final destination wrt. VM patches and 2.5.
> 

I'd prefer to do this at the vma level if poss.  Given that mmap_mem()
has set VM_RESERVED against the VMA, it should be sufficient to do

diff -puN mm/memory.c~a mm/memory.c
--- 25/mm/memory.c~a	2003-02-18 02:40:01.000000000 -0800
+++ 25-akpm/mm/memory.c	2003-02-18 02:40:18.000000000 -0800
@@ -211,6 +211,9 @@ int copy_page_range(struct mm_struct *ds
 	unsigned long cow;
 	struct pte_chain *pte_chain = NULL;
 
+	if (vma->vm_flags & (VM_RESERVED|VM_IO))
+		return 0;
+
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst, src, vma);
 
diff -puN fs/hugetlbfs/inode.c~a fs/hugetlbfs/inode.c
--- 25/fs/hugetlbfs/inode.c~a	2003-02-18 02:42:47.000000000 -0800
+++ 25-akpm/fs/hugetlbfs/inode.c	2003-02-18 02:42:55.000000000 -0800
@@ -63,7 +63,7 @@ static int hugetlbfs_file_mmap(struct fi
 	down(&inode->i_sem);
 
 	UPDATE_ATIME(inode);
-	vma->vm_flags |= VM_HUGETLB | VM_RESERVED;
+	vma->vm_flags |= VM_HUGETLB;
 	vma->vm_ops = &hugetlb_vm_ops;
 	ret = hugetlb_prefault(mapping, vma);
 	len = (loff_t)(vma->vm_end - vma->vm_start) +

_
 

The semantics (and usage!) of the VM_foo flags are rather vague.  It needs
definiton, and an audit.