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

[Andrew Morton <akpm@digeo.com>]

On reflection, I think your approach is best - there is (some) value in being
able to inherit a /dev/mem mapping across fork(), and ceasing to do so may
break applications.

I recast your patch a little.  Saves a few instructions and prevents a bogus
uninitialised variable warning.


diff -puN mm/memory.c~copy_page_range-invalid-page-fix mm/memory.c
--- 25/mm/memory.c~copy_page_range-invalid-page-fix	2003-03-01 17:26:03.000000000 -0800
+++ 25-akpm/mm/memory.c	2003-03-01 17:26:29.000000000 -0800
@@ -286,9 +286,11 @@ skip_copy_pte_range:
 					goto cont_copy_pte_range_noset;
 				}
 				pfn = pte_pfn(pte);
+				if (!pfn_valid(pfn)) {
+					set_pte(dst_pte, pte);
+					goto cont_copy_pte_range_noset;
+				}
 				page = pfn_to_page(pfn);
-				if (!pfn_valid(pfn))
-					goto cont_copy_pte_range;
 				if (PageReserved(page))
 					goto cont_copy_pte_range;
 

_

Xavier Bru  <Xavier.Bru@bull.net> wrote:
>
> Works OK for us.
> Thanks
> 
> -- 
> 
> _____________________________________________________________________
>  
> Xavier BRU                 BULL ISD/R&D/INTEL office:     FREC B1-422
> tel : +33 (0)4 76 29 77 45                    http://www-frec.bull.fr
> fax : +33 (0)4 76 29 77 70                 mailto:Xavier.Bru@bull.net
> addr: BULL, 1 rue de Provence, BP 208, 38432 Echirolles Cedex, FRANCE
> _____________________________________________________________________
> 
> Andrew Morton writes:
>  > 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.
>  > 
> 
> 
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