From f822566165dd46ff5de9bf895cfa6c51f53bb0c4 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" <mst@mellanox.co.il> Date: Tue, 14 Feb 2006 13:53:08 -0800 Subject: [PATCH] madvise MADV_DONTFORK/MADV_DOFORK Currently, copy-on-write may change the physical address of a page even if the user requested that the page is pinned in memory (either by mlock or by get_user_pages). This happens if the process forks meanwhile, and the parent writes to that page. As a result, the page is orphaned: in case of get_user_pages, the application will never see any data hardware DMA's into this page after the COW. In case of mlock'd memory, the parent is not getting the realtime/security benefits of mlock. In particular, this affects the Infiniband modules which do DMA from and into user pages all the time. This patch adds madvise options to control whether memory range is inherited across fork. Useful e.g. for when hardware is doing DMA from/into these pages. Could also be useful to an application wanting to speed up its forks by cutting large areas out of consideration. Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il> Acked-by: Hugh Dickins <hugh@veritas.com> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> --- include/asm-x86_64/mman.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/asm-x86_64/mman.h') diff --git a/include/asm-x86_64/mman.h b/include/asm-x86_64/mman.h index d0e97b74f735..b699a38c1c3c 100644 --- a/include/asm-x86_64/mman.h +++ b/include/asm-x86_64/mman.h @@ -37,6 +37,8 @@ #define MADV_WILLNEED 0x3 /* pre-fault pages */ #define MADV_DONTNEED 0x4 /* discard these pages */ #define MADV_REMOVE 0x5 /* remove these pages & resources */ +#define MADV_DONTFORK 0x30 /* dont inherit across fork */ +#define MADV_DOFORK 0x31 /* do inherit across fork */ /* compatibility flags */ #define MAP_ANON MAP_ANONYMOUS -- cgit v1.2.3