linux-kernel - [RFC/RFT PATCH v2 0/1] arc: add sparsemem support

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Date:   Thu,  9 Jul 2020 16:44:11 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Vineet Gupta <vgupta@...opsys.com>
Cc:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        Mike Rapoport <rppt@...nel.org>,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: [RFC/RFT PATCH v2 0/1] arc: add sparsemem support

From: Mike Rapoport <rppt@...ux.ibm.com>

Hi,

It took me a while to get back to it, but better late than never :)

This patch adds SPARSEMEM support as an alternative to DISCONTIGMEM in
the case when there are two DRAM banks populated.

I've verified that it boots on nsim, but I could not find a way to make
nsim emulate two memory banks.

There is slight improvement in the resulting kernel size for
nsim_700_defconfig with CONFIG_HIGHMEM=y.

If sparse actually works on a system with 2 DRAM banks and does not
introduce performance regression, I suggest to update this patch to
replace DISCONTIGMEM with SPARSEMEM on arc.

$ size discontig/vmlinux  sparse/vmlinux 
   text	   data	    bss	    dec	    hex	filename
3894379	1093092	 244932	5232403	 4fd713	discontig/vmlinux
3879040	1093964	 244956	5217960	 4f9ea8	sparse/vmlinux

$ ./scripts/bloat-o-meter ~/tmp/arc/discontig/vmlinux  ~/tmp/arc/sparse/vmlinux 
add/remove: 35/23 grow/shrink: 35/384 up/down: 8110/-26438 (-18328)
...
Total: Before=4282217, After=4263889, chg -0.43%


Mike Rapoport (1):
  arc: add sparsemem support

 arch/arc/Kconfig                 | 10 ++++++++++
 arch/arc/include/asm/sparsemem.h | 13 +++++++++++++
 arch/arc/mm/init.c               |  7 ++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 arch/arc/include/asm/sparsemem.h

-- 
2.26.2