linux-kernel - Re: [PATCH 3/3] mm/mmap.c: extract __vma_unlink_list as counter part for __vma_link

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Message-ID: <20190821080904.GA29221@richard>
Date:   Wed, 21 Aug 2019 16:09:04 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        osalvador@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/mmap.c: extract __vma_unlink_list as counter part
 for __vma_link_list

On Tue, Aug 20, 2019 at 06:59:39PM -0700, Matthew Wilcox wrote:
>On Wed, Aug 21, 2019 at 09:22:44AM +0800, Wei Yang wrote:
>> On Tue, Aug 20, 2019 at 05:54:17PM -0700, Matthew Wilcox wrote:
>> >On Wed, Aug 21, 2019 at 08:52:34AM +0800, Wei Yang wrote:
>> >> On Tue, Aug 20, 2019 at 10:26:29AM -0700, Matthew Wilcox wrote:
>> >> >On Wed, Aug 14, 2019 at 11:19:37AM +0200, Vlastimil Babka wrote:
>> >> >> On 8/14/19 8:57 AM, Wei Yang wrote:
>> >> >> > On Tue, Aug 13, 2019 at 10:16:11PM -0700, Christoph Hellwig wrote:
>> >> >> >>Btw, is there any good reason we don't use a list_head for vma linkage?
>> >> >> > 
>> >> >> > Not sure, maybe there is some historical reason?
>> >> >> 
>> >> >> Seems it was single-linked until 2010 commit 297c5eee3724 ("mm: make the vma
>> >> >> list be doubly linked") and I guess it was just simpler to add the vm_prev link.
>> >> >> 
>> >> >> Conversion to list_head might be an interesting project for some "advanced
>> >> >> beginner" in the kernel :)
>> >> >
>> >> >I'm working to get rid of vm_prev and vm_next, so it would probably be
>> >> >wasted effort.
>> >> 
>> >> You mean replace it with list_head?
>> >
>> >No, replace the rbtree with a new tree.  https://lwn.net/Articles/787629/
>> 
>> Sounds interesting.
>> 
>> While I am not sure the plan is settled down, and how long it would take to
>> replace the rb_tree with maple tree. I guess it would probably take some time
>> to get merged upstream.
>> 
>> IMHO, it would be good to have this cleanup in current kernel. Do you agree?
>
>The three cleanups you've posted are fine.  Doing more work (ie the
>list_head) seems like wasted effort to me.

Ah, got your point. I misunderstand it.

-- 
Wei Yang
Help you, Help me