Re: [MM] Make mm counters per cpu instead of atomic

Zhang, Yanmin
2009-11-17T06:46:16Z

On Wed, 2009-11-04 at 14:14 -0500, Christoph Lameter wrote:
> From: Christoph Lameter <cl@linux-foundation.org>
> Subject: Make mm counters per cpu
>
> Changing the mm counters to per cpu counters is possible after the introduction
> of the generic per cpu operations (currently in percpu and -next).
>
> With that the contention on the counters in mm_struct can be avoided. The
> USE_SPLIT_PTLOCKS case distinction can go away. Larger SMP systems do not
> need to perform atomic updates to mm counters anymore. Various code paths
> can be simplified since per cpu counter updates are fast and batching
> of counter updates is no longer needed.
>
> One price to pay for these improvements is the need to scan over all percpu
> counters when the actual count values are needed.
>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
>
> ---
> fs/proc/task_mmu.c | 14 +++++++++-
> include/linux/mm_types.h | 16 ++++--------
> include/linux/sched.h | 61 ++++++++++++++++++++---------------------------
> kernel/fork.c | 25 ++++++++++++++-----
> mm/filemap_xip.c | 2 -
> mm/fremap.c | 2 -
> mm/init-mm.c | 3 ++
> mm/memory.c | 20 +++++++--------
> mm/rmap.c | 10 +++----
> mm/swapfile.c | 2 -
> 10 files changed, 84 insertions(+), 71 deletions(-)
>
> Index: linux-2.6/include/linux/mm_types.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm_types.h 2009-11-04 13:08:33.000000000 -0600
> +++ linux-2.6/include/linux/mm_types.h 2009-11-04 13:13:42.000000000 -0600
> @@ -24,11 +24,10 @@ struct address_space;

> Index: linux-2.6/kernel/fork.c
> ===================================================================
> --- linux-2.6.orig/kernel/fork.c 2009-11-04 13:08:33.000000000 -0600
> +++ linux-2.6/kernel/fork.c 2009-11-04 13:14:19.000000000 -0600
> @@ -444,6 +444,8 @@ static void mm_init_aio(struct mm_struct
>
> static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
> {
> + int cpu;
> +
> atomic_set(&mm->mm_users, 1);
> atomic_set(&mm->mm_count, 1);
> init_rwsem(&mm->mmap_sem);
> @@ -452,8 +454,11 @@ static struct mm_struct * mm_init(struct
> (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
> mm->core_state = NULL;
> mm->nr_ptes = 0;
> - set_mm_counter(mm, file_rss, 0);
> - set_mm_counter(mm, anon_rss, 0);
> + for_each_possible_cpu(cpu) {
> + struct mm_counter *m;
> +
> + memset(m, sizeof(struct mm_counter), 0);
Above memset is wrong.
1) m isn't initiated;
2) It seems the 2nd and the 3rd parameters should be interchanged.