Re: [patch 1/1] MM: detach_vmas_to_be_unmapped fix

[akuster <akuster@mvista.com>]

Ingo Oeser wrote:
> Hi,
>
> On Wednesday, 21. February 2007, akuster@mvista.com wrote:
> > ---
> >
> >  mm/mmap.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff -puN mm/mmap.c~Avoiding-mmap-fragmentation_fixup mm/mmap.c
> > --- linux-2.6_clean/mm/mmap.c~Avoiding-mmap-fragmentation_fixup	2007-02-21 09:49:32.000000000 -0800
> > +++ linux-2.6_clean-akuster/mm/mmap.c	2007-02-21 09:51:26.000000000 -0800
> > @@ -1720,9 +1720,9 @@ detach_vmas_to_be_unmapped(struct mm_str
> >  	*insertion_point = vma;
> >  	tail_vma->vm_next = NULL;
> >  	if (mm->unmap_area == arch_unmap_area)
> > -		addr = prev ? prev->vm_end : mm->mmap_base;
> > +		addr = prev ? prev->vm_start : mm->mmap_base;
> >  	else
> > -		addr = vma ?  vma->vm_start : mm->mmap_base;
> > +		addr = vma ?  vma->vm_end : mm->mmap_base;
> >  	mm->unmap_area(mm, addr);
> >  	mm->mmap_cache = NULL;		/* Kill the cache. */
> >  }
>
> Please comment, why you think this is necessary.

Yes that would help.

On Feb. 16th I asked a question and got no response. Here is what should 
have been included with the above patch.

Wolfgang Wander submitted a fix to address a mmap fragmentation issue. 
The git patch ( 1363c3cd8603a913a27e2995dccbd70d5312d8e6 ) is somewhat 
different and yields different results when running Wolfgang's test case 
leakme.c.

IMHO, the vm start and end address are swapped in arch_unmap_area and 
arch_unmap_area_topdown functions.

Prior to this patch arch_unmap_area() used area->vm_start and 
arch_unmap_area_topdown used area->vm_end in the git patch the following 
change showed up.

if (mm->unmap_area == arch_unmap_area)
    addr = prev ? prev->vm_start : mm->mmap_base;
else
    addr = vma ?  vma->vm_end : mm->mmap_base;

Using Wolfgang Wander's leakme.c test, I get the same results seen with 
his original "Avoiding mmap fragmentation" patch as I do after swapping 
 the start & end address in the above code segment. The patch I 
submitted  addresses this typo issue.

TIA,
Armin

> Thanks & Regards
>
> Ingo Oeser
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