linux-kernel - Re: [RFC] mm: change find

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Message-Id: <35FEEB7C-1C74-4BF9-B2F2-EDB48996BD4F@gmail.com>
Date:	Tue, 22 Dec 2015 13:31:21 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chen Gang <gang.chen.5i5j@...il.com>, mhocko@...e.com,
	kwapulinski.piotr@...il.com,
	Andrea Arcangeli <aarcange@...hat.com>, dcashman@...gle.com,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm: change find_vma() function


> On Dec 15, 2015, at 19:53, Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:
> 
> On Tue, Dec 15, 2015 at 02:41:21PM +0800, yalin wang wrote:
>>> On Dec 15, 2015, at 05:11, Kirill A. Shutemov <kirill@...temov.name> wrote:
>>> 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,
> 
> Do you have any workload which can demonstrate the advantage?
> 
> — 
i add the log in find_vma() to see the call stack ,
it is very efficient in mmap() / munmap / do_execve() / get_unmaped_area() /
mem_cgroup_move_task()->walk_page_range()->find_vma() call ,

in most time the loop will break after search about 7 vm,
i don’t consider the cache pollution problem in this patch,
yeah, this patch will check the vm_prev->vm_end for every loop,
but this only happened when tmp->vm_end > addr ,
if you don’t not check this , you will continue to loop to check next rb ,
this will also pollute the cache ,

so the question is which one is better ?
i don’t have a better method to test this .
Any good ideas about this ?
how to test it ?

Thanks







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