Re: [PATCH v2] smaps should deal with huge zero page exactly same as normal zero page.

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 27 Oct 2014 23:02:13 +0800 Fengwei Yin <yfw.kernel@gmail.com> wrote:

> We could see following memory info in /proc/xxxx/smaps with THP enabled.
>   7bea458b3000-7fea458b3000 r--p 00000000 00:13 39989  /dev/zero
>   Size:           4294967296 kB
>   Rss:            10612736 kB
>   Pss:            10612736 kB
>   Shared_Clean:          0 kB
>   Shared_Dirty:          0 kB
>   Private_Clean:  10612736 kB
>   Private_Dirty:         0 kB
>   Referenced:     10612736 kB
>   Anonymous:             0 kB
>   AnonHugePages:  10612736 kB
>   Swap:                  0 kB
>   KernelPageSize:        4 kB
>   MMUPageSize:           4 kB
>   Locked:                0 kB
>   VmFlags: rd mr mw me
> which is wrong becuase just huge_zero_page/normal_zero_page is used for
> /dev/zero. Most of the value should be 0.
> 
> This patch detects huge_zero_page (original implementation just detect
> normal_zero_page) and avoids to update the wrong value for huge_zero_page.
> 
> ...
>
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -41,6 +41,7 @@
>  #include <linux/kernel_stat.h>
>  #include <linux/mm.h>
>  #include <linux/hugetlb.h>
> +#include <linux/huge_mm.h>
>  #include <linux/mman.h>
>  #include <linux/swap.h>
>  #include <linux/highmem.h>
> @@ -787,6 +788,9 @@ check_pfn:
>  		return NULL;
>  	}
>  
> +	if (is_huge_zero_pfn(pfn))
> +		return NULL;
> +

Why this change?

What effect does it have upon vm_normal_page()'s many existing callers?

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>