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

Zhang, Yanmin
2009-11-17T07:29:25Z

On Tue, 2009-11-17 at 14:48 +0800, Zhang, Yanmin wrote:
> 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.
Changing it to below fixes the command hang issue.

for_each_possible_cpu(cpu) {
struct mm_counter *m = per_cpu(mm->rss->readers, cpu);

memset(m, 0, sizeof(struct mm_counter));
}