From 61cd52d4e44d7d8c55dad939b1877fd39d7103a2 Mon Sep 17 00:00:00 2001 From: Matt Redfearn Date: Thu, 31 Mar 2016 10:05:38 +0100 Subject: [PATCH] MIPS: bootmem: When relocatable, free memory below kernel The kernel reserves all memory before the _end symbol as bootmem, however, once the kernel can be relocated elsewhere in memory this may result in a large amount of wasted memory. The assumption is that the memory between the link and relocated address of the kernel may be released back to the available memory pool. Memory statistics for a Malta with the kernel relocating by 16Mb, without the patch: Memory: 105952K/131072K available (4604K kernel code, 242K rwdata, 892K rodata, 1280K init, 183K bss, 25120K reserved, 0K cma-reserved) And with the patch: Memory: 122336K/131072K available (4604K kernel code, 242K rwdata, 892K rodata, 1280K init, 183K bss, 8736K reserved, 0K cma-reserved) The 16Mb offset is removed from the reserved region and added back to the available region. Signed-off-by: Matt Redfearn Cc: Aaro Koskinen Cc: Masahiro Yamada Cc: Alexander Sverdlin Cc: Jaedon Shin Cc: James Hogan Cc: Jonas Gorski Cc: Paul Burton Cc: linux-mips@linux-mips.org Cc: kernel-hardening@lists.openwall.com Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/12986/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/setup.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c index d20caacfdbd3..3378fdaf4dd3 100644 --- a/arch/mips/kernel/setup.c +++ b/arch/mips/kernel/setup.c @@ -469,6 +469,20 @@ static void __init bootmem_init(void) */ reserve_bootmem(PFN_PHYS(mapstart), bootmap_size, BOOTMEM_DEFAULT); +#ifdef CONFIG_RELOCATABLE + /* + * The kernel reserves all memory below its _end symbol as bootmem, + * but the kernel may now be at a much higher address. The memory + * between the original and new locations may be returned to the system. + */ + if (__pa_symbol(_text) > __pa_symbol(VMLINUX_LOAD_ADDRESS)) { + unsigned long offset; + + offset = __pa_symbol(_text) - __pa_symbol(VMLINUX_LOAD_ADDRESS); + free_bootmem(__pa_symbol(VMLINUX_LOAD_ADDRESS), offset); + } +#endif + /* * Reserve initrd memory if needed. */