linux-kernel - Re: [RFC PATCH 0/8] remove vm

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Message-ID: <CAA_GA1fiQfOqApE05oh=2Wr-GejbHtOd4o7sqcGdQFH6cxWPpQ@mail.gmail.com>
Date:	Fri, 7 Dec 2012 11:37:30 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 0/8] remove vm_struct list management

Hi Joonsoo,

On Fri, Dec 7, 2012 at 12:09 AM, Joonsoo Kim <js1304@...il.com> wrote:
> This patchset remove vm_struct list management after initializing vmalloc.
> Adding and removing an entry to vmlist is linear time complexity, so
> it is inefficient. If we maintain this list, overall time complexity of
> adding and removing area to vmalloc space is O(N), although we use
> rbtree for finding vacant place and it's time complexity is just O(logN).
>
> And vmlist and vmlist_lock is used many places of outside of vmalloc.c.
> It is preferable that we hide this raw data structure and provide
> well-defined function for supporting them, because it makes that they
> cannot mistake when manipulating theses structure and it makes us easily
> maintain vmalloc layer.
>
> I'm not sure that "7/8: makes vmlist only for kexec" is fine.
> Because it is related to userspace program.
> As far as I know, makedumpfile use kexec's output information and it only
> need first address of vmalloc layer. So my implementation reflect this
> fact, but I'm not sure. And now, I don't fully test this patchset.
> Basic operation work well, but I don't test kexec. So I send this
> patchset with 'RFC'.
>
> Please let me know what I am missing.
>

Nice work!
I also thought about this several weeks ago but I think the efficiency
may be a problem.

As you know two locks(vmap_area_lock and vmlist_lock) are used
currently so that some
work may be done in parallel(not proved).
If removed vmlist, i'm afraid vmap_area_lock will become a bottleneck
which will reduce the efficiency.

> This series based on v3.7-rc7 and on top of submitted patchset for ARM.
> 'introduce static_vm for ARM-specific static mapped area'
> https://lkml.org/lkml/2012/11/27/356
> But, running properly on x86 without ARM patchset.
>
> Joonsoo Kim (8):
>   mm, vmalloc: change iterating a vmlist to find_vm_area()
>   mm, vmalloc: move get_vmalloc_info() to vmalloc.c
>   mm, vmalloc: protect va->vm by vmap_area_lock
>   mm, vmalloc: iterate vmap_area_list, instead of vmlist in
>     vread/vwrite()
>   mm, vmalloc: iterate vmap_area_list in get_vmalloc_info()
>   mm, vmalloc: iterate vmap_area_list, instead of vmlist, in
>     vmallocinfo()
>   mm, vmalloc: makes vmlist only for kexec
>   mm, vmalloc: remove list management operation after initializing
>     vmalloc
>
>  arch/tile/mm/pgtable.c      |    7 +-
>  arch/unicore32/mm/ioremap.c |   17 +--
>  arch/x86/mm/ioremap.c       |    7 +-
>  fs/proc/Makefile            |    2 +-
>  fs/proc/internal.h          |   18 ---
>  fs/proc/meminfo.c           |    1 +
>  fs/proc/mmu.c               |   60 ----------
>  include/linux/vmalloc.h     |   19 +++-
>  mm/vmalloc.c                |  258 +++++++++++++++++++++++++++++--------------
>  9 files changed, 204 insertions(+), 185 deletions(-)
>  delete mode 100644 fs/proc/mmu.c
>
> --
> 1.7.9.5
>

-- 
Regards,
--Bob
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