linux-kernel - Re: linux-next: manual merge of the akpm tree with Linus' tree

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Message-Id: <20120307235012.847af577.akpm@linux-foundation.org>
Date:	Wed, 7 Mar 2012 23:50:12 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus <torvalds@...ux-foundation.org>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree

On Thu, 8 Mar 2012 18:41:05 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:

> Hi Andrew,
> 
> On Wed, 7 Mar 2012 23:32:20 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > Actually they're different.  I reworked the earlier patch as below.
> 
> OK.  But some comments.
> 
> > diff -puN arch/x86/mm/hugetlbpage.c~hugetlb-drop-prev_vma-in-hugetlb_get_unmapped_area_topdown arch/x86/mm/hugetlbpage.c
> > --- a/arch/x86/mm/hugetlbpage.c~hugetlb-drop-prev_vma-in-hugetlb_get_unmapped_area_topdown
> > +++ a/arch/x86/mm/hugetlbpage.c
> > @@ -308,7 +308,7 @@ static unsigned long hugetlb_get_unmappe
> >  {
> >  	struct hstate *h = hstate_file(file);
> >  	struct mm_struct *mm = current->mm;
> > -	struct vm_area_struct *vma, *prev_vma;
> > +	struct vm_area_struct *vma;
> 
> You still remove prev_vma ...
> 
> >  	unsigned long base = mm->mmap_base, addr = addr0;
> >  	unsigned long largest_hole = mm->cached_hole_size;
> >  	int first_time = 1;
> > @@ -334,25 +334,16 @@ try_again:
> >  		 * i.e. return with success:
> >  		 */
> >  		vma = find_vma(mm, addr);
> > -		if (!vma)
> > -			return addr;
> > -
> > -		/*
> > -		 * new region fits between prev_vma->vm_end and
> > -		 * vma->vm_start, use it:
> > -		 */
> > -		prev_vma = vma->vm_prev;
> > -		if (addr + len <= vma->vm_start &&
> > -		            (!prev_vma || (addr >= prev_vma->vm_end))) {
> > +		if (vma)
> > +			prev_vma = vma->vm_prev;
> 
> But then assign to it ...
> 
> > +		if (!vma || addr + len <= vma->vm_start) {
> >  			/* remember the address as a hint for next time */
> >  		        mm->cached_hole_size = largest_hole;
> >  		        return (mm->free_area_cache = addr);
> > -		} else {
> > +		} else if (mm->free_area_cache == vma->vm_end) {
> >  			/* pull free_area_cache down to the first hole */
> > -		        if (mm->free_area_cache == vma->vm_end) {
> > -				mm->free_area_cache = vma->vm_start;
> > -				mm->cached_hole_size = largest_hole;
> > -			}
> > +			mm->free_area_cache = vma->vm_start;
> > +			mm->cached_hole_size = largest_hole;
> >  		}
> >  
> >  		/* remember the largest hole we saw so far */
> 
> But it never gets used.

Doh.  The author reviewed that for me too!

I'll drop it - please rework, retest and resend?

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