Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()

From: Vlastimil Babka
Date: Tue Jul 11 2017 - 02:56:21 EST

On 07/11/2017 08:50 AM, Michal Hocko wrote:
> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote:
>> On 07/11/2017 08:03 AM, Michal Hocko wrote:
>>> Are you telling me that two if conditions cause more than a second
>>> difference? That sounds suspicious.
>> It's removing also a call to get_unmapped_area(), AFAICS. That means a
>> vma search?
> Ohh, right. I have somehow missed that. Is this removal intentional?

I think it is: "Checking for availability of virtual address range at
the end of the VMA for the incremental size is also reduntant at this

> The
> changelog is silent about it.

It doesn't explain why it's redundant, indeed. Unfortunately, the commit
f106af4e90ea ("fix checks for expand-in-place mremap") which added this,
also doesn't explain why it's needed.