On Wed, Nov 20, 2013 at 05:42:11PM +0000, Al Viro wrote:
> [Apologies for delay; I'd spent the last day hunting down something that
> turned out to be a VM leak completely unrelated to this stuff - it's
> present in mainline, for starters. Unreliable reproducers make for fun
> bisects ;-/ Anyway, by now I'm absolutely sure that this is a VM bug and
> not something I had somehow managed to break, so...]
BTW, something odd happened to mm/memory.c - either a mangled patch
or a lost followup. Take a look at the last commit in there:
commit ea1e7ed33708c7a760419ff9ded0a6cb90586a50
Author: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Thu Nov 14 14:31:53 2013 -0800
mm: create a separate slab for page->ptl allocation
If DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC are enabled spinlock_t on x86_64
is 72 bytes. For page->ptl they will be allocated from kmalloc-96 slab,
so we loose 24 on each. An average system can easily allocate few tens
thousands of page->ptl and overhead is significant.
Let's create a separate slab for page->ptl allocation to solve this.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Fair enough, and yes, it does create that separate slab. The problem is,
it's still using kmalloc/kfree for those beasts - page_ptl_cachep isn't
used at all...
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