Message-ID: <557E911F.5040602@jp.fujitsu.com>
Date: Mon, 15 Jun 2015 17:47:27 +0900
From: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: "Luck, Tony" <tony.luck@intel.com>, Xishi Qiu <qiuxishi@huawei.com>
CC: Andrew Morton <akpm@linux-foundation.org>,
        "nao.horiguchi@gmail.com" <nao.horiguchi@gmail.com>,
        Yinghai Lu <yinghai@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, "mingo@elte.hu" <mingo@elte.hu>,
        Xiexiuqi <xiexiuqi@huawei.com>, Hanjun Guo <guohanjun@huawei.com>,
        Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 10/12] mm: add the buddy system interface
References: <55704A7E.5030507@huawei.com> <55704CC4.8040707@huawei.com> <557691E0.5020203@jp.fujitsu.com> <5576BA2B.6060907@huawei.com> <5577A9A9.7010108@jp.fujitsu.com> <3908561D78D1C84285E8C5FCA982C28F32A8F209@ORSMSX114.amr.corp.intel.com>
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On 2015/06/11 5:40, Luck, Tony wrote:
>> I guess, mirrored memory should be allocated if !__GFP_HIGHMEM or !__GFP_MOVABLE
>
> HIGHMEM shouldn't matter - partial memory mirror only makes any sense on X86_64 systems ... 32-bit kernels
> don't even boot on systems with 64GB, and the minimum rational configuration for a machine that supports
> mirror is 128GB (4 cpu sockets * 2 memory controller per socket * 4 channels per controller * 4GB DIMM ...
> leaving any channels empty likely leaves you short of memory bandwidth for these high core count processors).
>
> MOVABLE is mostly the opposite of MIRROR - we never want to fill a kernel allocation from a MOVABLE page. I
> want all kernel allocations to be from MIRROR.
>

So, there are 3 ideas.

  (1) kernel only from MIRROR / user only from MOVABLE (Tony)
  (2) kernel only from MIRROR / user from MOVABLE + MIRROR(ASAP)  (AKPM suggested)
      This makes use of the fact MOVABLE memory is reclaimable but Tony pointed out
      the memory reclaim can be critical for GFP_ATOMIC.
  (3) kernel only from MIRROR / user from MOVABLE, special user from MIRROR (Xishi)

2 Implementation ideas.
   - creating ZONE
   - creating new alloation attribute

I don't convince whether we need some new structure in mm. Isn't it good to use
ZONE_MOVABLE for not-mirrored memory ?
Then, disable fallback from ZONE_MOVABLE -> ZONE_NORMAL for (1) and (3)

Thanks,
-Kame


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