linux-kernel - Re: 答复: [PATCH] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP

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Message-ID: <20200722124910.GE27540@gaia>
Date:   Wed, 22 Jul 2020 13:49:10 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     "liwei (CM)" <liwei213@...wei.com>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>,
        "will@...nel.org" <will@...nel.org>,
        "Xiaqing (A)" <saberlily.xia@...ilicon.com>,
        "Chenfeng (puck)" <puck.chen@...ilicon.com>,
        butao <butao@...ilicon.com>,
        fengbaopeng <fengbaopeng2@...ilicon.com>,
        "nsaenzjulienne@...e.de" <nsaenzjulienne@...e.de>,
        "steve.capper@....com" <steve.capper@....com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        sujunfei <sujunfei2@...ilicon.com>,
        zhaojiapeng <zhaojiapeng@...wei.com>
Subject: Re: 答复: [PATCH] arm64: mm: free unused memmap for sparse memory model
 that define VMEMMAP

On Wed, Jul 22, 2020 at 08:41:17AM +0000, liwei (CM) wrote:
> Mike Rapoport wrote:
> > On Tue, Jul 21, 2020 at 03:32:03PM +0800, Wei Li wrote:
> > > For the memory hole, sparse memory model that define SPARSEMEM_VMEMMAP 
> > > do not free the reserved memory for the page map, this patch do it.
> > 
> > Are there numbers showing how much memory is actually freed?
> > 
> > The freeing of empty memmap would become rather complex with these
> > changes, do the memory savings justify it?
> 
> In the sparse memory model, the size of a section is 1 GB
> (SECTION_SIZE_BITS 30) by default.

Can we reduce SECTION_SIZE_BITS instead? Say 26?

-- 
Catalin