On Mon, Dec 14, 2015 at 06:55:09PM +0100, Oleg Nesterov wrote: > On 12/14, Kirill A. Shutemov wrote: > > > > On Mon, Dec 14, 2015 at 07:02:25PM +0800, yalin wang wrote: > > > change find_vma() to break ealier when found the adderss > > > is not in any vma, don't need loop to search all vma. > > > > > > Signed-off-by: yalin wang <yalin.wang2010@xxxxxxxxx> > > > --- > > > mm/mmap.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > > index b513f20..8294c9b 100644 > > > --- a/mm/mmap.c > > > +++ b/mm/mmap.c > > > @@ -2064,6 +2064,9 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) > > > vma = tmp; > > > if (tmp->vm_start <= addr) > > > break; > > > + if (!tmp->vm_prev || tmp->vm_prev->vm_end <= addr) > > > + break; > > > + > > > > This 'break' would return 'tmp' as found vma. > > But this would be right? Hm. Right. Sorry for my tone. I think the right condition is 'tmp->vm_prev->vm_end < addr', not '<=' as vm_end is the first byte after the vma. But it's equivalent in practice here. Anyway, I don't think it's possible to gain anything measurable from this optimization. > > Not that I think this optimization makes sense, I simply do not know, > but to me this change looks technically correct at first glance... > > But the changelog is wrong or I missed something. This change can stop > the main loop earlier; if "tmp" is the first vma, For the first vma, we don't get anything comparing to what we have now: check for !rb_node on the next iteration would have the same trade off and effect as the proposed check. > or if the previous one is below the address. Yes, but would it compensate additional check on each 'tmp->vm_end > addr' iteration to the point? That's not obvious. > Or perhaps I just misread that "not in any vma" note in the changelog. > > No? > > Oleg. > -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>