Subject: Re: [PATCH 0/2] ARM: Allow either FLATMEM or SPARSEMEM on the multiplatform build

From: Russell King - ARM Linux admin <[email-masked]>
Date: Thu, 21 May 2020 13:03:08 +0100

On Thu, May 21, 2020 at 11:18:23AM +0300, Mike Rapoport wrote:
> (resendig for the correct address and with mailing list cc'ed, sorry for
> the noise)
> 
> Hi,
> 
> Following the discussion at [1], I'm resending the patches that enable
> memory model selection in menuconfig and such.
> 
> These patches do not change the way the configuration is generated from the
> defconfigs and they do not change explicit selection of SPARSEMEM for
> platforms that have "select ARCH_ENABLE_SPARSEMEM".
> 
> The mere change is that when a user runs an interactive configuration they
> will be allowed to select between FLATMEM and SPARSMEM, which is not the
> case today.
> 
> There is indeed some awkwardness in, e.g. removal of
> ARCH_SPARSEMEM_DEFAULT, but this is what memory model selection logic in
> mm/Kconfig imposes.
> 
> For example, below is the diffs of the configurations generated with
> 'make rpc_defconfig' and 'make defconfig':
> 
> $ diff -s old/rpc_defconfig new/rpc_defconfig
> Files old/rpc_defconfig and new/rpc_defconfig are identical
> 
> $ diff -u old/defconfig new/defconfig
> --- old/defconfig	2020-05-20 17:51:01.832649705 +0300
> +++ new/defconfig	2020-05-20 18:15:21.084385880 +0300
> @@ -674,6 +674,9 @@
>  CONFIG_AEABI=y
>  # CONFIG_OABI_COMPAT is not set
>  CONFIG_ARCH_HAS_HOLES_MEMORYMODEL=y
> +CONFIG_ARCH_SELECT_MEMORY_MODEL=y
> +CONFIG_ARCH_FLATMEM_ENABLE=y
> +CONFIG_ARCH_SPARSEMEM_ENABLE=y
>  CONFIG_HAVE_ARCH_PFN_VALID=y
>  CONFIG_HIGHMEM=y
>  CONFIG_HIGHPTE=y
> @@ -1061,6 +1064,9 @@
>  #
>  # Memory Management options
>  #
> +CONFIG_SELECT_MEMORY_MODEL=y
> +CONFIG_FLATMEM_MANUAL=y
> +# CONFIG_SPARSEMEM_MANUAL is not set
>  CONFIG_FLATMEM=y
>  CONFIG_FLAT_NODE_MEM_MAP=y
>  CONFIG_ARCH_KEEP_MEMBLOCK=y

Right, but the question is whether we want to offer flatmem for rpc.
It isn't allowed today, and so far no one has said why it's a
desirable change to make.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up

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