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From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Pavel Tatashin <pasha.tatashin@soleen.com>,
	jmorris@namei.org, sashal@kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-nvdimm@lists.01.org, akpm@linux-foundation.org,
	mhocko@suse.com, dave.hansen@linux.intel.com,
	dan.j.williams@intel.com, keith.busch@intel.com,
	vishal.l.verma@intel.com, dave.jiang@intel.com,
	zwisler@kernel.org, thomas.lendacky@amd.com,
	ying.huang@intel.com, fengguang.wu@intel.com, bp@suse.de,
	bhelgaas@google.com, baiyaowei@cmss.chinamobile.com,
	tiwai@suse.de, jglisse@redhat.com, catalin.marinas@arm.com,
	will.deacon@arm.com, rppt@linux.vnet.ibm.com,
	ard.biesheuvel@linaro.org, andrew.murray@arm.com,
	james.morse@arm.com, marc.zyngier@arm.com, sboyd@kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: configurable sparsemem section size
Date: Wed, 24 Apr 2019 14:37:11 +0530	[thread overview]
Message-ID: <7f7499bd-8d48-945b-6d69-60685a02c8da@arm.com> (raw)
In-Reply-To: <20190423203843.2898-1-pasha.tatashin@soleen.com>



On 04/24/2019 02:08 AM, Pavel Tatashin wrote:
> sparsemem section size determines the maximum size and alignment that
> is allowed to offline/online memory block. The bigger the size the less
> the clutter in /sys/devices/system/memory/*. On the other hand, however,
> there is less flexability in what granules of memory can be added and
> removed.

Is there any scenario where less than a 1GB needs to be added on arm64 ?

> 
> Recently, it was enabled in Linux to hotadd persistent memory that
> can be either real NV device, or reserved from regular System RAM
> and has identity of devdax.

devdax (even ZONE_DEVICE) support has not been enabled on arm64 yet.

> 
> The problem is that because ARM64's section size is 1G, and devdax must
> have 2M label section, the first 1G is always missed when device is
> attached, because it is not 1G aligned.

devdax has to be 2M aligned ? Does Linux enforce that right now ?

> 
> Allow, better flexibility by making section size configurable.

Unless 2M is being enforced from Linux not sure why this is necessary at
the moment.

> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> ---
>  arch/arm64/Kconfig                 | 10 ++++++++++
>  arch/arm64/include/asm/sparsemem.h |  2 +-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b5d8cf57e220..a0c5b9d13a7f 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -801,6 +801,16 @@ config ARM64_PA_BITS
>  	default 48 if ARM64_PA_BITS_48
>  	default 52 if ARM64_PA_BITS_52
>  
> +config ARM64_SECTION_SIZE_BITS
> +	int "sparsemem section size shift"
> +	range 27 30

27 and 28 do not even compile for ARM64_64_PAGES because of MAX_ORDER and
SECTION_SIZE mismatch.

  reply	other threads:[~2019-04-24  9:07 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-23 20:38 [PATCH] arm64: configurable sparsemem section size Pavel Tatashin
2019-04-24  9:07 ` Anshuman Khandual [this message]
2019-04-24 19:48   ` Pavel Tatashin
2019-04-24 19:54     ` Pavel Tatashin
2019-04-24 20:24       ` Dan Williams
2019-04-24 20:33         ` Pavel Tatashin
2019-04-25  3:06     ` Anshuman Khandual
2019-04-25 15:25 ` Michal Hocko
2019-04-25 15:31   ` Will Deacon
2019-04-25 15:41     ` Michal Hocko
2019-04-25 17:57       ` Pavel Tatashin
2019-04-26  5:33         ` Michal Hocko

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