linux-kernel - Re: [PATCH] arm64: configurable sparsemem section size

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Date:   Thu, 25 Apr 2019 13:57:25 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Will Deacon <will.deacon@....com>,
        James Morris <jmorris@...ei.org>,
        Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Takashi Iwai <tiwai@...e.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        rppt@...ux.vnet.ibm.com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        andrew.murray@....com, james.morse@....com,
        Marc Zyngier <marc.zyngier@....com>, sboyd@...nel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: configurable sparsemem section size

> > I gave *vague* memories of running out of bits in the page flags if we
> > changed this, but that was a while back. If that's no longer the case,
> > then I'm open to changing the value, but I really don't want to expose
> > it as a Kconfig option as proposed in this patch. People won't have a
> > clue what to set and it doesn't help at all with the single-Image effort.
>
> Ohh, I absolutely agree about the config option part JFTR. 1GB section
> loos quite excessive. I am not really sure a standard arm64 memory
> layout looks though.

I am now looking to use Dan's patches "mm: Sub-section memory hotplug
support" to solve this problem. I think this patch can be ignored.

Pasha