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Date: Mon, 11 Jan 2010 10:20:22 +0800
From: "Zheng, Shaohui" <shaohui.zheng@...el.com>
To: "Wu, Fengguang" <fengguang.wu@...el.com>
CC: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"ak@...ux.intel.com" <ak@...ux.intel.com>,
"y-goto@...fujitsu.com" <y-goto@...fujitsu.com>,
Dave Hansen <haveblue@...ibm.com>,
"x86@...nel.org" <x86@...nel.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: RE: [PATCH - resend] Memory-Hotplug: Fix the bug on interface
/dev/mem for 64-bit kernel(v1)
Thanks Fengguang, see and comments in the email. Only a few different understanding on variable max_low_pfn.
Thanks & Regards,
Shaohui
-----Original Message-----
From: Wu, Fengguang
Sent: Friday, January 08, 2010 8:49 PM
To: Zheng, Shaohui
Cc: linux-mm@...ck.org; akpm@...ux-foundation.org; linux-kernel@...r.kernel.org; ak@...ux.intel.com; y-goto@...fujitsu.com; Dave Hansen; x86@...nel.org; KAMEZAWA Hiroyuki
Subject: Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel(v1)
On Fri, Jan 08, 2010 at 11:32:07AM +0800, Zheng, Shaohui wrote:
> Resend the patch to the mailing-list, the original patch URL is
> http://patchwork.kernel.org/patch/69075/, it is not accepted without comments,
> sent it again to review.
>
> Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel
>
> The new added memory can not be access by interface /dev/mem, because we do not
> update the variable high_memory. This patch add a new e820 entry in e820 table,
> and update max_pfn, max_low_pfn and high_memory.
>
> We add a function update_pfn in file arch/x86/mm/init.c to udpate these
> varibles. Memory hotplug does not make sense on 32-bit kernel, so we did not
> concern it in this function.
>
> Signed-off-by: Shaohui Zheng <shaohui.zheng@...el.com>
> CC: Andi Kleen <ak@...ux.intel.com>
> CC: Wu Fengguang <fengguang.wu@...el.com>
> CC: Li Haicheng <Haicheng.li@...el.com>
>
> ---
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index f50447d..b986246 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -110,8 +110,8 @@ int __init e820_all_mapped(u64 start, u64 end, unsigned type)
> /*
> * Add a memory region to the kernel e820 map.
> */
> -static void __init __e820_add_region(struct e820map *e820x, u64 start, u64 size,
> - int type)
> +static void __meminit __e820_add_region(struct e820map *e820x, u64 start,
> + u64 size, int type)
> {
> int x = e820x->nr_map;
>
> @@ -126,7 +126,7 @@ static void __init __e820_add_region(struct e820map *e820x, u64 start, u64 size,
> e820x->nr_map++;
> }
>
> -void __init e820_add_region(u64 start, u64 size, int type)
> +void __meminit e820_add_region(u64 start, u64 size, int type)
> {
> __e820_add_region(&e820, start, size, type);
> }
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index d406c52..0474459 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -1,6 +1,7 @@
> #include <linux/initrd.h>
> #include <linux/ioport.h>
> #include <linux/swap.h>
> +#include <linux/bootmem.h>
>
> #include <asm/cacheflush.h>
> #include <asm/e820.h>
> @@ -386,3 +387,30 @@ void free_initrd_mem(unsigned long start, unsigned long end)
> free_init_pages("initrd memory", start, end);
> }
> #endif
> +
> +/**
> + * After memory hotplug, the variable max_pfn, max_low_pfn and high_memory will
> + * be affected, it will be updated in this function. Memory hotplug does not
> + * make sense on 32-bit kernel, so we do did not concern it in this function.
> + */
> +void __meminit __attribute__((weak)) update_pfn(u64 start, u64 size)
> +{
> +#ifdef CONFIG_X86_64
> + unsigned long limit_low_pfn = 1UL<<(32 - PAGE_SHIFT);
> + unsigned long start_pfn = start >> PAGE_SHIFT;
> + unsigned long end_pfn = (start + size) >> PAGE_SHIFT;
Strictly speaking, should use "end_pfn = PFN_UP(start + size);".
[Zheng, Shaohui] I will use PFN_UP to replace it in new version.
> + if (end_pfn > max_pfn) {
> + max_pfn = end_pfn;
> + high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
> + }
> +
> + /* if add to low memory, update max_low_pfn */
> + if (unlikely(start_pfn < limit_low_pfn)) {
> + if (end_pfn <= limit_low_pfn)
> + max_low_pfn = end_pfn;
> + else
> + max_low_pfn = limit_low_pfn;
X86_64 actually always set max_low_pfn=max_pfn, in setup_arch():
[Zheng, Shaohui] there should be some misunderstanding, I read the code carefully, if the total memory is under 4G, it always max_low_pfn=max_pfn. If the total memory is larger than 4G, max_low_pfn means the end of low ram. It set max_low_pfn = e820_end_of_low_ram_pfn();.
899 #ifdef CONFIG_X86_64
900 if (max_pfn > max_low_pfn) {
901 max_pfn_mapped = init_memory_mapping(1UL<<32,
902 max_pfn<<PAGE_SHIFT);
903 /* can we preseve max_low_pfn ?*/
904 max_low_pfn = max_pfn;
905 }
906 #endif
max_low_pfn is used in
- e820_mark_nosave_regions(max_low_pfn);
- dump_pagetable()
- blk_queue_bounce_limit()
- increase_reservation()
and _seems_ to mean "end of direct addressable pfn".
> + }
> +#endif /* CONFIG_X86_64 */
> +}
> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> index b10ec49..6693414 100644
> --- a/include/linux/bootmem.h
> +++ b/include/linux/bootmem.h
> @@ -13,6 +13,7 @@
>
> extern unsigned long max_low_pfn;
> extern unsigned long min_low_pfn;
> +extern void update_pfn(u64 start, u64 size);
>
> /*
> * highest page
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 030ce8a..ee7b2d6 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -523,6 +523,14 @@ int __ref add_memory(int nid, u64 start, u64 size)
> BUG_ON(ret);
> }
>
> + /* update e820 table */
This comment can be eliminated - you already have the very readable printk :)
[Zheng, Shaohui] I will remove this comment
> + printk(KERN_INFO "Adding memory region to e820 table (start:%016Lx, size:%016Lx).\n",
> + (unsigned long long)start, (unsigned long long)size);
> + e820_add_region(start, size, E820_RAM);
> + /* update max_pfn, max_low_pfn and high_memory */
> + update_pfn(start, size);
How about renaming function to update_end_of_memory_vars()?
[Zheng, Shaohui] Agree.
Thanks,
Fengguang
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