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: <20190821015939.GA28819@bombadil.infradead.org>
Date:   Tue, 20 Aug 2019 18:59:39 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     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 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.