Re: [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag

[Dave Hansen <dave.hansen@intel.com>]

On 10/17/2014 07:09 AM, Dominik Dingel wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cd33ae2..8f09c91 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -113,7 +113,7 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_GROWSDOWN	0x00000100	/* general info on the segment */
>  #define VM_PFNMAP	0x00000400	/* Page-ranges managed without "struct page", just pure PFN */
>  #define VM_DENYWRITE	0x00000800	/* ETXTBSY on write attempts.. */
> -
> +#define VM_NOZEROPAGE	0x00001000	/* forbid new zero page mappings */
>  #define VM_LOCKED	0x00002000
>  #define VM_IO           0x00004000	/* Memory mapped I/O or similar */

This seems like an awfully obscure use for a very constrained resource
(VM_ flags).

Is there ever a time where the VMAs under an mm have mixed VM_NOZEROPAGE
status?  Reading the patches, it _looks_ like it might be an all or
nothing thing.

Full disclosure: I've got an x86-specific feature I want to steal a flag
for.  Maybe we should just define another VM_ARCH bit.

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