On Tue, 8 Nov 2005, Michael S. Tsirkin wrote:
>
> Hugh, did you have something like the following in mind
> (this is only boot-tested and only on x86-64)?
Yes, that looks pretty good to me, a few comments below.
Only another twenty or so architectures to go ;)
(I had been imagining VM_DONTCOPY plus another flag to say set by the
user: better your way, we would like to merge these vmas, and VM_DONTCOPY
is in that peculiar list of special flags that prevent merging.)
> Hmm, maybe MADV_INHERIT and MADV_DONT_INHERIT would be better names,
You're right, and it would be a good choice, except that MAP_INHERIT on
some OSes has a particular meaning (about inheriting across an exec),
so I think avoid confusion with that. MADV_DONTFORK and MADV_DOFORK?
Accompanied by VM_DONTFORK?
> since the copy is only dont one write ...
"only done on write"?
> Index: linux-2.6.14-dontcopy/include/linux/mm.h
> ===================================================================
> --- linux-2.6.14-dontcopy.orig/include/linux/mm.h 2005-11-08 23:24:58.000000000 +0200
> +++ linux-2.6.14-dontcopy/include/linux/mm.h 2005-11-08 23:25:09.000000000 +0200
> @@ -154,6 +154,7 @@ extern unsigned int kobjsize(const void
> /* Used by sys_madvise() */
> #define VM_SEQ_READ 0x00008000 /* App will access data sequentially */
> #define VM_RAND_READ 0x00010000 /* App will not benefit from clustered reads */
> +#define VM_UDONTCOPY 0x02000000 /* App wants to set VM_DONTCOPY */
Please place it where you'd expect to find it by value.
> #define VM_DONTCOPY 0x00020000 /* Do not copy this vma on fork */
> #define VM_DONTEXPAND 0x00040000 /* Cannot expand with mremap() */
> Index: linux-2.6.14-dontcopy/include/asm-x86_64/mman.h
> ===================================================================
> --- linux-2.6.14-dontcopy.orig/include/asm-x86_64/mman.h 2005-11-08 23:19:35.000000000 +0200
> +++ linux-2.6.14-dontcopy/include/asm-x86_64/mman.h 2005-11-08 23:19:46.000000000 +0200
> @@ -36,6 +36,8 @@
> #define MADV_SEQUENTIAL 0x2 /* read-ahead aggressively */
> #define MADV_WILLNEED 0x3 /* pre-fault pages */
> #define MADV_DONTNEED 0x4 /* discard these pages */
> +#define MADV_DONTCOPY 0x30 /* dont inherit across fork */
> +#define MADV_DOCOPY 0x31 /* do inherit across fork */
>
> /* compatibility flags */
> #define MAP_ANON MAP_ANONYMOUS
I think that's probably a good idea, to choose a range away from the rest.
But I'm not quite sure: anyone familiar with adding APIs listening?
Hugh
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