> On Dec 15, 2015, at 05:11, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > 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. > this should be <= here, because vma’s effect address space doesn’t include vm_end add, so if an address vm_end <= add , this means this addr don’t belong to this vma, > Anyway, I don't think it's possible to gain anything measurable from this > optimization. > the advantage is that if addr don’t belong to any vma, we don’t need loop all vma, we can break earlier if we found the most closest vma which vma->end_add > addr, >> >> 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. Yes > >> 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. >> i have test it, it works fine. :) Thanks -- 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