[PATCH] free e820 reserved memory in bootargs memmap

[PATCH] free e820 reserved memory in bootargs memmap

[zoucao]

add a new chareater "-" in bootargs memmap, you can use this chareater to free
e820 reserved memory, for example:

reserved iomem:
	cat /proc/iomem:
	......
	00100000-6aefefff : System RAM
	  01000000-0165537a : Kernel code
	  0165537b-01a8873f : Kernel data
	  01c31000-01f4efff : Kernel bss
	  28000000-320fffff : Crash kernel
	6aeff000-6effffff : reserved       --> it is e820 reserved memory
	6f000000-78240fff : System RAM
	......


add bootargs memmap=0x4101000-0x6aeff000, to free memory region: 6aeff000-6effffff
then 6aeff000-6effffff will be merged into 00100000-78240fff.

new iomem:  
	cat /proc/iomem:
	......
	00100000-78240fff : System RAM
	  01000000-0165537a : Kernel code
	  0165537b-01a8873f : Kernel data
	  01c31000-01f4efff : Kernel bss
	......

[PATCH] x86/boot/e820: add new chareater "-" to free BIOS memory in memmap bootargs

[zoucao]

From: zoucao <zoucao@linux.alibaba.com>

Normally every BIOS reserved memory is used for some features, we can
not use them, but in some conditions,  users can ensure some BIOS memorys
are not used and reserved memory is well to free, they have not a good
way to free these memroys, here add a new chareater "-" in memmap to free
reserved memory.

Signed-off-by: zou cao <zoucao@linux.alibaba.com>
---
 7u/Documentation/kernel-parameters.txt | 6 ++++++
 7u/arch/x86/kernel/e820.c              | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/7u/Documentation/kernel-parameters.txt b/7u/Documentation/kernel-parameters.txt
index 9a1abb99a..dbea75e12 100644
--- a/7u/Documentation/kernel-parameters.txt
+++ b/7u/Documentation/kernel-parameters.txt
@@ -1677,6 +1677,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			         or
 			         memmap=0x10000$0x18690000
 
+	memmap=nn[KMG]-ss[KMG]
+			Free E820 reserved memory, as specified by the user.
+			Region of reserved memory to be free, from ss to ss+nn.
+			Example: free reserved memory from 0x18690000-0x186a0000
+					memmap=0x4101000-0x6aeff000
+
 	memory_corruption_check=0/1 [X86]
 			Some BIOSes seem to corrupt the first 64k of
 			memory when doing things like suspend/resume.
diff --git a/7u/arch/x86/kernel/e820.c b/7u/arch/x86/kernel/e820.c
index 174da5fc5..b8a042981 100644
--- a/7u/arch/x86/kernel/e820.c
+++ b/7u/arch/x86/kernel/e820.c
@@ -875,6 +875,9 @@ static int __init parse_memmap_one(char *p)
 	} else if (*p == '$') {
 		start_at = memparse(p+1, &p);
 		e820_add_region(start_at, mem_size, E820_RESERVED);
+	} else if (*p == '-') {
+		start_at = memparse(p+1, &p);
+		e820_remove_range(start_at, mem_size, E820_RESERVED, E820_RAM);
 	} else
 		e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
 
-- 
2.14.1.40.g8e62ba1

Re: [PATCH] free e820 reserved memory in bootargs memmap

[zoucao-ipc]

I found commit characters errors, please ignore this path, V2 will be 
sent soon

On 2018/4/8 下午2:41, zoucao@linux.alibaba.com wrote:
> add a new chareater "-" in bootargs memmap, you can use this chareater to free
> e820 reserved memory, for example:
>
> reserved iomem:
> 	cat /proc/iomem:
> 	......
> 	00100000-6aefefff : System RAM
> 	  01000000-0165537a : Kernel code
> 	  0165537b-01a8873f : Kernel data
> 	  01c31000-01f4efff : Kernel bss
> 	  28000000-320fffff : Crash kernel
> 	6aeff000-6effffff : reserved       --> it is e820 reserved memory
> 	6f000000-78240fff : System RAM
> 	......
>
>
> add bootargs memmap=0x4101000-0x6aeff000, to free memory region: 6aeff000-6effffff
> then 6aeff000-6effffff will be merged into 00100000-78240fff.
>
> new iomem:
> 	cat /proc/iomem:
> 	......
> 	00100000-78240fff : System RAM
> 	  01000000-0165537a : Kernel code
> 	  0165537b-01a8873f : Kernel data
> 	  01c31000-01f4efff : Kernel bss
> 	......