path: root/mm/Kconfig.debug
diff options
authorJoonsoo Kim <>2014-12-12 16:55:46 -0800
committerLinus Torvalds <>2014-12-13 12:42:48 -0800
commiteefa864b701d78dc9753c70a3540a2e9ae192595 (patch)
treeac638eef9f41b5857a11191f3e6e455c64778df2 /mm/Kconfig.debug
parent2d48366b3ff745729815c15077508f8d7722ec5f (diff)
mm/page_ext: resurrect struct page extending code for debugging
When we debug something, we'd like to insert some information to every page. For this purpose, we sometimes modify struct page itself. But, this has drawbacks. First, it requires re-compile. This makes us hesitate to use the powerful debug feature so development process is slowed down. And, second, sometimes it is impossible to rebuild the kernel due to third party module dependency. At third, system behaviour would be largely different after re-compile, because it changes size of struct page greatly and this structure is accessed by every part of kernel. Keeping this as it is would be better to reproduce errornous situation. This feature is intended to overcome above mentioned problems. This feature allocates memory for extended data per page in certain place rather than the struct page itself. This memory can be accessed by the accessor functions provided by this code. During the boot process, it checks whether allocation of huge chunk of memory is needed or not. If not, it avoids allocating memory at all. With this advantage, we can include this feature into the kernel in default and can avoid rebuild and solve related problems. Until now, memcg uses this technique. But, now, memcg decides to embed their variable to struct page itself and it's code to extend struct page has been removed. I'd like to use this code to develop debug feature, so this patch resurrect it. To help these things to work well, this patch introduces two callbacks for clients. One is the need callback which is mandatory if user wants to avoid useless memory allocation at boot-time. The other is optional, init callback, which is used to do proper initialization after memory is allocated. Detailed explanation about purpose of these functions is in code comment. Please refer it. Others are completely same with previous extension code in memcg. Signed-off-by: Joonsoo Kim <> Cc: Mel Gorman <> Cc: Johannes Weiner <> Cc: Minchan Kim <> Cc: Dave Hansen <> Cc: Michal Nazarewicz <> Cc: Jungsoo Son <> Cc: Ingo Molnar <> Cc: Joonsoo Kim <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/Kconfig.debug')
1 files changed, 9 insertions, 0 deletions
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 4b2443254de2..1ba81c7769f7 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -1,3 +1,12 @@
+ bool "Extend memmap on extra space for more information on page"
+ ---help---
+ Extend memmap on extra space for more information on page. This
+ could be used for debugging features that need to insert extra
+ field for every page. This extension enables us to save memory
+ by not allocating this extra memory according to boottime
+ configuration.
bool "Debug page memory allocations"
depends on DEBUG_KERNEL