Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
To:     "liwei (CM)" <liwei213@huawei.com>,
        "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
        "rppt@linux.ibm.com" <rppt@linux.ibm.com>,
        "will@kernel.org" <will@kernel.org>
CC:     fengbaopeng <fengbaopeng2@hisilicon.com>,
        "nsaenzjulienne@suse.de" <nsaenzjulienne@suse.de>,
        "steve.capper@arm.com" <steve.capper@arm.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        butao <butao@hisilicon.com>
Subject: RE: [PATCH] arm64: mm: decrease the section size to reduce the memory
 reserved for the page map
Thread-Topic: [PATCH] arm64: mm: decrease the section size to reduce the
 memory reserved for the page map
Thread-Index: AQHWyd8Pm9rJc08RmUuZbQcVlySHKKnmKYSA
Date:   Fri, 4 Dec 2020 01:50:40 +0000
Message-ID: <731f9389df474a968b2799fa698821da@hisilicon.com>
References: <20201204014443.43329-1-liwei213@huawei.com>
In-Reply-To: <20201204014443.43329-1-liwei213@huawei.com>
Accept-Language: en-GB, en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Precedence: bulk


> -----Original Message-----
> From: liwei (CM)
> Sent: Friday, December 4, 2020 2:45 PM
> To: catalin.marinas@arm.com; rppt@linux.ibm.com; will@kernel.org; liwei (CM)
> <liwei213@huawei.com>
> Cc: fengbaopeng <fengbaopeng2@hisilicon.com>; nsaenzjulienne@suse.de;
> steve.capper@arm.com; Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; butao
> <butao@hisilicon.com>
> Subject: [PATCH] arm64: mm: decrease the section size to reduce the memory
> reserved for the page map
> 
> For the memory hole, sparse memory model that define SPARSEMEM_VMEMMAP
> do not free the reserved memory for the page map, decrease the section
> size can reduce the waste of reserved memory.
> 
> Signed-off-by: Wei Li <liwei213@huawei.com>
> Signed-off-by: Baopeng Feng <fengbaopeng2@hisilicon.com>
> Signed-off-by: Xia Qing <saberlily.xia@hisilicon.com>
> ---

Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>

When page size is 4K, for each 1GB memory, we need 16MB vmemmap;
For each 128MB memory, we need 2MB vmemmap.

So while we have memory hole like 928MB(1GB-64MB),if SECTION_SIZE_BITS
is 30, we waste 15MB; if SECTION_SIZE_BITS is 27, we waste 1MB only.

>  arch/arm64/include/asm/sparsemem.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/sparsemem.h
> b/arch/arm64/include/asm/sparsemem.h
> index 1f43fcc79738..8963bd3def28 100644
> --- a/arch/arm64/include/asm/sparsemem.h
> +++ b/arch/arm64/include/asm/sparsemem.h
> @@ -7,7 +7,7 @@
> 
>  #ifdef CONFIG_SPARSEMEM
>  #define MAX_PHYSMEM_BITS	CONFIG_ARM64_PA_BITS
> -#define SECTION_SIZE_BITS	30
> +#define SECTION_SIZE_BITS	27
>  #endif
> 
>  #endif
> --
> 2.15.0

Thanks
Barry