Re: [RFC][mmotm][PATCH] percpu mm struct counter cache

[Minchan Kim <minchan.kim@gmail.com>]

Hi, Kame.

KAMEZAWA Hiroyuki wrote:
> Christophs's mm_counter+percpu implemtation has scalability at updates but
> read-side had some problems. Inspired by that, I tried to write percpu-cache
> counter + synchronization method. My own tiny benchmark shows something good
> but this patch's hooks may summon other troubles...
> 
> Now, I start from sharing codes here. Any comments are welcome.
> (Especially, moving hooks to somewhere better is my concern.)
> My test proram will be posted in reply to this mail.
> 
> Regards,
> -Kame
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> This patch is for implemanting light-weight per-mm statistics.
> Now, when split-pagetable-lock is used, statistics per mm struct
> is maintainer by atomic_long_t value. This costs one atomic_inc()
> under page_table_lock and if multi-thread program runs and shares
> mm_struct, this tend to cause cache-miss+atomic_ops.

Both cases are (page_table_lock + atomic inc) cost?

AFAIK, 
If we don't use split lock, we get the just spinlock of page_table_lock. 
If we use split lock, we get the just atomic_op cost + page->ptl lock.
In case of split lock, ptl lock contention for rss accounting is little, I think.

If I am wrong, could you write down changelog more clearly?


> 
> This patch adds per-cpu mm statistics cache and sync it in periodically.
> Cached Information are synchronized into mm_struct at
>   - tick
>   - context_switch.
>   if there is difference.

Should we sync mm statistics periodically?
Couldn't we sync statistics when we need it?
ex) get_mm_counter.
I am not sure it's possible. :)

> 
> Tiny test progam on x86-64/4core/2socket machine shows (small) improvements.
> This test program measures # of page faults on cpu  0 and 4.
> (Using all 8cpus, most of time is used for spinlock and you can't see
>  benefits of this patch..)
> 
> [Before Patch]
> Performance counter stats for './multi-fault 2' (5 runs):
> 
>        44282223  page-faults                ( +-   0.912% )
>      1015540330  cache-references           ( +-   1.701% )
>       210497140  cache-misses               ( +-   0.731% )
>  29262804803383988  bus-cycles                 ( +-   0.003% )
> 
>    60.003401467  seconds time elapsed   ( +-   0.004% )
> 
>  4.75 miss/faults
>  660825108.1564714580837551899777 bus-cycles/faults
> 
> [After Patch]
> Performance counter stats for './multi-fault 2' (5 runs):
> 
>        45543398  page-faults                ( +-   0.499% )
>      1031865896  cache-references           ( +-   2.720% )
>       184901499  cache-misses               ( +-   0.626% )
>  29261889737265056  bus-cycles                 ( +-   0.002% )
> 
>    60.001218501  seconds time elapsed   ( +-   0.000% )
> 
>  4.05 miss/faults
>  642505632.5 bus-cycles/faults
> 
> Note: to enable split-pagetable-lock, you have to disable SPINLOCK_DEBUG.
> 
> This patch moves mm_counter definitions to mm.h+memory.c from sched.h.
> So, total patch size seems to be big.

What's your goal/benefit?
You cut down atomic operations with (cache and sync) method?

Please, write down the your goal/benefit. :)

> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  fs/proc/task_mmu.c       |    4 -
>  include/linux/mm.h       |   55 ++++++++++++++++++
>  include/linux/mm_types.h |   23 +++++--
>  include/linux/sched.h    |   54 ------------------
>  kernel/exit.c            |    4 +
>  kernel/fork.c            |    3 -
>  kernel/sched.c           |    1 
>  kernel/timer.c           |    2 
>  mm/filemap_xip.c         |    2 
>  mm/fremap.c              |    2 
>  mm/memory.c              |  139 ++++++++++++++++++++++++++++++++++++++++++-----
>  mm/oom_kill.c            |    4 -
>  mm/rmap.c                |   10 +--
>  mm/swapfile.c            |    2 
>  14 files changed, 217 insertions(+), 88 deletions(-)
> 
> Index: mmotm-2.6.32-Nov24/include/linux/mm_types.h
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/include/linux/mm_types.h
> +++ mmotm-2.6.32-Nov24/include/linux/mm_types.h
> @@ -24,11 +24,6 @@ struct address_space;
>  
>  #define USE_SPLIT_PTLOCKS	(NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS)
>  
> -#if USE_SPLIT_PTLOCKS
> -typedef atomic_long_t mm_counter_t;
> -#else  /* !USE_SPLIT_PTLOCKS */
> -typedef unsigned long mm_counter_t;
> -#endif /* !USE_SPLIT_PTLOCKS */
>  
>  /*
>   * Each physical page in the system has a struct page associated with
> @@ -199,6 +194,21 @@ struct core_state {
>  	struct completion startup;
>  };
>  
> +/*
> + * for per-mm accounting.
> + */
> +#if USE_SPLIT_PTLOCKS
> +typedef atomic_long_t mm_counter_t;
> +#else  /* !USE_SPLIT_PTLOCKS */
> +typedef unsigned long mm_counter_t;
> +#endif /* !USE_SPLIT_PTLOCKS */
> +
> +enum {
> +	MM_FILEPAGES,
> +	MM_ANONPAGES,
> +	NR_MM_STATS,
> +};
> +
>  struct mm_struct {
>  	struct vm_area_struct * mmap;		/* list of VMAs */
>  	struct rb_root mm_rb;
> @@ -226,8 +236,7 @@ struct mm_struct {
>  	/* Special counters, in some configurations protected by the
>  	 * page_table_lock, in other configurations by being atomic.
>  	 */
> -	mm_counter_t _file_rss;
> -	mm_counter_t _anon_rss;
> +	mm_counter_t counters[NR_MM_STATS];
>  
>  	unsigned long hiwater_rss;	/* High-watermark of RSS usage */
>  	unsigned long hiwater_vm;	/* High-water virtual memory usage */
> Index: mmotm-2.6.32-Nov24/include/linux/sched.h
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/include/linux/sched.h
> +++ mmotm-2.6.32-Nov24/include/linux/sched.h
> @@ -385,60 +385,6 @@ arch_get_unmapped_area_topdown(struct fi
>  extern void arch_unmap_area(struct mm_struct *, unsigned long);
>  extern void arch_unmap_area_topdown(struct mm_struct *, unsigned long);
>  
> -#if USE_SPLIT_PTLOCKS
> -/*
> - * The mm counters are not protected by its page_table_lock,
> - * so must be incremented atomically.
> - */
> -#define set_mm_counter(mm, member, value) atomic_long_set(&(mm)->_##member, value)
> -#define get_mm_counter(mm, member) ((unsigned long)atomic_long_read(&(mm)->_##member))
> -#define add_mm_counter(mm, member, value) atomic_long_add(value, &(mm)->_##member)
> -#define inc_mm_counter(mm, member) atomic_long_inc(&(mm)->_##member)
> -#define dec_mm_counter(mm, member) atomic_long_dec(&(mm)->_##member)
> -
> -#else  /* !USE_SPLIT_PTLOCKS */
> -/*
> - * The mm counters are protected by its page_table_lock,
> - * so can be incremented directly.
> - */
> -#define set_mm_counter(mm, member, value) (mm)->_##member = (value)
> -#define get_mm_counter(mm, member) ((mm)->_##member)
> -#define add_mm_counter(mm, member, value) (mm)->_##member += (value)
> -#define inc_mm_counter(mm, member) (mm)->_##member++
> -#define dec_mm_counter(mm, member) (mm)->_##member--
> -
> -#endif /* !USE_SPLIT_PTLOCKS */
> -
> -#define get_mm_rss(mm)					\
> -	(get_mm_counter(mm, file_rss) + get_mm_counter(mm, anon_rss))
> -#define update_hiwater_rss(mm)	do {			\
> -	unsigned long _rss = get_mm_rss(mm);		\
> -	if ((mm)->hiwater_rss < _rss)			\
> -		(mm)->hiwater_rss = _rss;		\
> -} while (0)
> -#define update_hiwater_vm(mm)	do {			\
> -	if ((mm)->hiwater_vm < (mm)->total_vm)		\
> -		(mm)->hiwater_vm = (mm)->total_vm;	\
> -} while (0)
> -
> -static inline unsigned long get_mm_hiwater_rss(struct mm_struct *mm)
> -{
> -	return max(mm->hiwater_rss, get_mm_rss(mm));
> -}
> -
> -static inline void setmax_mm_hiwater_rss(unsigned long *maxrss,
> -					 struct mm_struct *mm)
> -{
> -	unsigned long hiwater_rss = get_mm_hiwater_rss(mm);
> -
> -	if (*maxrss < hiwater_rss)
> -		*maxrss = hiwater_rss;
> -}
> -
> -static inline unsigned long get_mm_hiwater_vm(struct mm_struct *mm)
> -{
> -	return max(mm->hiwater_vm, mm->total_vm);
> -}
>  
>  extern void set_dumpable(struct mm_struct *mm, int value);
>  extern int get_dumpable(struct mm_struct *mm);
> Index: mmotm-2.6.32-Nov24/mm/memory.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/memory.c
> +++ mmotm-2.6.32-Nov24/mm/memory.c
> @@ -121,6 +121,115 @@ static int __init init_zero_pfn(void)
>  }
>  core_initcall(init_zero_pfn);
>  
> +
> +#ifdef USE_SPLIT_PTLOCKS
> +
> +struct pcp_mm_cache {
> +	struct mm_struct *mm;
> +	long counters[NR_MM_STATS];
> +};
> +static DEFINE_PER_CPU(struct pcp_mm_cache, curr_mmc);
> +/*
> + * The mm counters are not protected by its page_table_lock,
> + * so must be incremented atomically.
> + */
> +void set_mm_counter(struct mm_struct *mm, int member, long value)
> +{
> +	atomic_long_set(&mm->counters[member], value);
> +}
> +
> +unsigned long get_mm_counter(struct mm_struct *mm, int member)
> +{
> +	long ret = atomic_long_read(&mm->counters[member]);

Which case do we get the minus 'ret'?

> +	if (ret < 0)
> +		return 0;
> +	return ret;
> +}
> +
> +void add_mm_counter(struct mm_struct *mm, int member, long value)
> +{
> +	atomic_long_add(value, &mm->counters[member]);
> +}
> +
> +/*
> + * Always called under pte_lock....irq off, mm != curr_mmc.mm if called
> + * by get_user_pages() etc.
> + */
> +static void
> +add_mm_counter_fast(struct mm_struct *mm, int member, long val)
> +{
> +	if (likely(percpu_read(curr_mmc.mm) == mm))
> +		percpu_add(curr_mmc.counters[member], val);
> +	else
> +		add_mm_counter(mm, member, val);
> +}
> +
> +/* Called by not-preemptable context */
        	non-preemptible
> +void sync_tsk_mm_counters(void)
> +{
> +	struct pcp_mm_cache *cache = &per_cpu(curr_mmc, smp_processor_id());
> +	int i;
> +
> +	if (!cache->mm)
> +		return;
> +
> +	for (i = 0; i < NR_MM_STATS; i++) {
> +		if (!cache->counters[i])
> +			continue;
> +		add_mm_counter(cache->mm, i, cache->counters[i]);
> +		cache->counters[i] = 0;
> +	}
> +}
> +
> +void prepare_mm_switch(struct task_struct *prev, struct task_struct *next)
> +{
> +	if (prev->mm == next->mm)
> +		return;
> +	/* If task is exited, sync is already done and prev->mm is NULL */
> +	if (prev->mm)
> +		sync_tsk_mm_counters();
> +	percpu_write(curr_mmc.mm, next->mm);
> +}

Further optimization.
In case of (A-> kernel thread -> A), we don't need sync only if
we update statistics when we need it as i suggested.

> +
> +#else  /* !USE_SPLIT_PTLOCKS */
> +/*
> + * The mm counters are protected by its page_table_lock,
> + * so can be incremented directly.
> + */
> +void set_mm_counter(struct mm_struct *mm, int member, long value)
> +{
> +	mm->counters[member] = value;
> +}
> +
> +unsigned long get_mm_counter(struct mm_struct *mm, int member)
> +{
> +	return mm->counters[member];
> +}
> +
> +void add_mm_counter(struct mm_struct *mm, int member, long val)
> +{
> +	mm->counters[member] += val;
> +}
> +
> +void sync_tsk_mm_counters(struct task_struct *tsk)
> +{
> +}
> +
> +#define add_mm_counter_fast(mm, member, val) add_mm_counter(mm, member, val)
> +
> +#endif /* !USE_SPLIT_PTLOCKS */
> +/* Special asynchronous routine for page fault path */
> +#define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, 1)
> +#define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, -1)
> +
> +void init_mm_counters(struct mm_struct *mm)
> +{
> +	int i;
> +
> +	for (i = 0; i < NR_MM_STATS; i++)
> +		set_mm_counter(mm, i, 0);
> +}
> +
>  /*
>   * If a p?d_bad entry is found while walking page tables, report
>   * the error, before resetting entry to p?d_none.  Usually (but
> @@ -378,10 +487,11 @@ int __pte_alloc_kernel(pmd_t *pmd, unsig
>  
>  static inline void add_mm_rss(struct mm_struct *mm, int file_rss, int anon_rss)
>  {
> +	/* use synchronous updates here */
>  	if (file_rss)
> -		add_mm_counter(mm, file_rss, file_rss);
> +		add_mm_counter(mm, MM_FILEPAGES, file_rss);

We can divide MM_[FILEP|ANON]AGES on another patches. 
Things like rss[0] and rss[1] were not good. 


>  	if (anon_rss)
> -		add_mm_counter(mm, anon_rss, anon_rss);
> +		add_mm_counter(mm, MM_ANONPAGES, anon_rss);
>  }
>  
>  /*
> @@ -632,7 +742,10 @@ copy_one_pte(struct mm_struct *dst_mm, s
>  	if (page) {
>  		get_page(page);
>  		page_dup_rmap(page);
> -		rss[PageAnon(page)]++;
> +		if (PageAnon(page))
> +			rss[MM_ANONPAGES]++;
> +		else
> +			rss[MM_FILEPAGES]++;
>  	}
>  
>  out_set_pte:
> @@ -648,7 +761,7 @@ static int copy_pte_range(struct mm_stru
>  	pte_t *src_pte, *dst_pte;
>  	spinlock_t *src_ptl, *dst_ptl;
>  	int progress = 0;
> -	int rss[2];
> +	int rss[NR_MM_STATS];
>  	swp_entry_t entry = (swp_entry_t){0};
>  
>  again:
> @@ -688,7 +801,7 @@ again:
>  	arch_leave_lazy_mmu_mode();
>  	spin_unlock(src_ptl);
>  	pte_unmap_nested(orig_src_pte);
> -	add_mm_rss(dst_mm, rss[0], rss[1]);
> +	add_mm_rss(dst_mm, rss[MM_FILEPAGES], rss[MM_ANONPAGES]);
>  	pte_unmap_unlock(orig_dst_pte, dst_ptl);
>  	cond_resched();
>  
> @@ -1527,7 +1640,7 @@ static int insert_page(struct vm_area_st
>  
>  	/* Ok, finally just insert the thing.. */
>  	get_page(page);
> -	inc_mm_counter(mm, file_rss);
> +	inc_mm_counter_fast(mm, MM_FILEPAGES);
>  	page_add_file_rmap(page);
>  	set_pte_at(mm, addr, pte, mk_pte(page, prot));
>  
> @@ -2163,11 +2276,11 @@ gotten:
>  	if (likely(pte_same(*page_table, orig_pte))) {
>  		if (old_page) {
>  			if (!PageAnon(old_page)) {
> -				dec_mm_counter(mm, file_rss);
> -				inc_mm_counter(mm, anon_rss);
> +				dec_mm_counter_fast(mm, MM_FILEPAGES);
> +				inc_mm_counter_fast(mm, MM_ANONPAGES);
>  			}
>  		} else
> -			inc_mm_counter(mm, anon_rss);
> +			inc_mm_counter_fast(mm, MM_ANONPAGES);
>  		flush_cache_page(vma, address, pte_pfn(orig_pte));
>  		entry = mk_pte(new_page, vma->vm_page_prot);
>  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> @@ -2600,7 +2713,7 @@ static int do_swap_page(struct mm_struct
>  	 * discarded at swap_free().
>  	 */
>  
> -	inc_mm_counter(mm, anon_rss);
> +	inc_mm_counter_fast(mm, MM_ANONPAGES);
>  	pte = mk_pte(page, vma->vm_page_prot);
>  	if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
>  		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
> @@ -2684,7 +2797,7 @@ static int do_anonymous_page(struct mm_s
>  	if (!pte_none(*page_table))
>  		goto release;
>  
> -	inc_mm_counter(mm, anon_rss);
> +	inc_mm_counter_fast(mm, MM_ANONPAGES);
>  	page_add_new_anon_rmap(page, vma, address);
>  setpte:
>  	set_pte_at(mm, address, page_table, entry);
> @@ -2838,10 +2951,10 @@ static int __do_fault(struct mm_struct *
>  		if (flags & FAULT_FLAG_WRITE)
>  			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>  		if (anon) {
> -			inc_mm_counter(mm, anon_rss);
> +			inc_mm_counter_fast(mm, MM_ANONPAGES);
>  			page_add_new_anon_rmap(page, vma, address);
>  		} else {
> -			inc_mm_counter(mm, file_rss);
> +			inc_mm_counter_fast(mm, MM_FILEPAGES);
>  			page_add_file_rmap(page);
>  			if (flags & FAULT_FLAG_WRITE) {
>  				dirty_page = page;
> Index: mmotm-2.6.32-Nov24/kernel/fork.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/kernel/fork.c
> +++ mmotm-2.6.32-Nov24/kernel/fork.c
> @@ -452,8 +452,7 @@ 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);
> +	init_mm_counters(mm);
>  	spin_lock_init(&mm->page_table_lock);
>  	mm->free_area_cache = TASK_UNMAPPED_BASE;
>  	mm->cached_hole_size = ~0UL;
> Index: mmotm-2.6.32-Nov24/mm/fremap.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/fremap.c
> +++ mmotm-2.6.32-Nov24/mm/fremap.c
> @@ -40,7 +40,7 @@ static void zap_pte(struct mm_struct *mm
>  			page_remove_rmap(page);
>  			page_cache_release(page);
>  			update_hiwater_rss(mm);
> -			dec_mm_counter(mm, file_rss);
> +			dec_mm_counter(mm, MM_FILEPAGES);
>  		}
>  	} else {
>  		if (!pte_file(pte))
> Index: mmotm-2.6.32-Nov24/mm/rmap.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/rmap.c
> +++ mmotm-2.6.32-Nov24/mm/rmap.c
> @@ -815,9 +815,9 @@ int try_to_unmap_one(struct page *page, 
>  
>  	if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
>  		if (PageAnon(page))
> -			dec_mm_counter(mm, anon_rss);
> +			dec_mm_counter(mm, MM_ANONPAGES);
>  		else
> -			dec_mm_counter(mm, file_rss);
> +			dec_mm_counter(mm, MM_FILEPAGES);
>  		set_pte_at(mm, address, pte,
>  				swp_entry_to_pte(make_hwpoison_entry(page)));
>  	} else if (PageAnon(page)) {
> @@ -839,7 +839,7 @@ int try_to_unmap_one(struct page *page, 
>  					list_add(&mm->mmlist, &init_mm.mmlist);
>  				spin_unlock(&mmlist_lock);
>  			}
> -			dec_mm_counter(mm, anon_rss);
> +			dec_mm_counter(mm, MM_ANONPAGES);
>  		} else if (PAGE_MIGRATION) {
>  			/*
>  			 * Store the pfn of the page in a special migration
> @@ -857,7 +857,7 @@ int try_to_unmap_one(struct page *page, 
>  		entry = make_migration_entry(page, pte_write(pteval));
>  		set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
>  	} else
> -		dec_mm_counter(mm, file_rss);
> +		dec_mm_counter(mm, MM_FILEPAGES);
>  
>  	page_remove_rmap(page);
>  	page_cache_release(page);
> @@ -995,7 +995,7 @@ static int try_to_unmap_cluster(unsigned
>  
>  		page_remove_rmap(page);
>  		page_cache_release(page);
> -		dec_mm_counter(mm, file_rss);
> +		dec_mm_counter(mm, MM_FILEPAGES);
>  		(*mapcount)--;
>  	}
>  	pte_unmap_unlock(pte - 1, ptl);
> Index: mmotm-2.6.32-Nov24/mm/swapfile.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/swapfile.c
> +++ mmotm-2.6.32-Nov24/mm/swapfile.c
> @@ -839,7 +839,7 @@ static int unuse_pte(struct vm_area_stru
>  		goto out;
>  	}
>  
> -	inc_mm_counter(vma->vm_mm, anon_rss);
> +	add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);

Why can't we use inc_mm_counter_fast in here?

>  	get_page(page);
>  	set_pte_at(vma->vm_mm, addr, pte,
>  		   pte_mkold(mk_pte(page, vma->vm_page_prot)));
> Index: mmotm-2.6.32-Nov24/kernel/timer.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/kernel/timer.c
> +++ mmotm-2.6.32-Nov24/kernel/timer.c
> @@ -1200,6 +1200,8 @@ void update_process_times(int user_tick)
>  	account_process_tick(p, user_tick);
>  	run_local_timers();
>  	rcu_check_callbacks(cpu, user_tick);
> +	/* sync cached mm stat information */
> +	sync_tsk_mm_counters();
>  	printk_tick();
>  	scheduler_tick();
>  	run_posix_cpu_timers(p);
> Index: mmotm-2.6.32-Nov24/mm/filemap_xip.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/filemap_xip.c
> +++ mmotm-2.6.32-Nov24/mm/filemap_xip.c
> @@ -194,7 +194,7 @@ retry:
>  			flush_cache_page(vma, address, pte_pfn(*pte));
>  			pteval = ptep_clear_flush_notify(vma, address, pte);
>  			page_remove_rmap(page);
> -			dec_mm_counter(mm, file_rss);
> +			dec_mm_counter(mm, MM_FILEPAGES);
>  			BUG_ON(pte_dirty(pteval));
>  			pte_unmap_unlock(pte, ptl);
>  			page_cache_release(page);
> Index: mmotm-2.6.32-Nov24/include/linux/mm.h
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/include/linux/mm.h
> +++ mmotm-2.6.32-Nov24/include/linux/mm.h
> @@ -863,6 +863,61 @@ extern int mprotect_fixup(struct vm_area
>  			  struct vm_area_struct **pprev, unsigned long start,
>  			  unsigned long end, unsigned long newflags);
>  
> +/* For per-mm stat accounting */
> +extern void set_mm_counter(struct mm_struct *mm, int member, long value);
> +extern unsigned long get_mm_counter(struct mm_struct *mm, int member);
> +extern void add_mm_counter(struct mm_struct *mm, int member, long value);
> +extern void sync_tsk_mm_counters(void);
> +extern void init_mm_counters(struct mm_struct *mm);
> +
> +#ifdef USE_SPLIT_PTLOCKS
> +extern void prepare_mm_switch(struct task_struct *prev,
> +				 struct task_struct *next);
> +#else
> +static inline prepare_mm_switch(struct task_struct *prev,
> +				struct task_struct *next)
> +{
> +}
> +#endif
> +
> +#define inc_mm_counter(mm, member) add_mm_counter((mm), (member), 1)
> +#define dec_mm_counter(mm, member) add_mm_counter((mm), (member), -1)
> +
> +#define get_mm_rss(mm)			\
> +	(get_mm_counter(mm, MM_FILEPAGES) +\
> +	 get_mm_counter(mm, MM_ANONPAGES))
> +
> +#define update_hiwater_rss(mm)	do {			\
> +	unsigned long _rss = get_mm_rss(mm);		\
> +	if ((mm)->hiwater_rss < _rss)			\
> +		(mm)->hiwater_rss = _rss;		\
> +} while (0)
> +
> +#define update_hiwater_vm(mm)	do {			\
> +	if ((mm)->hiwater_vm < (mm)->total_vm)		\
> +		(mm)->hiwater_vm = (mm)->total_vm;	\
> +} while (0)
> +
> +static inline unsigned long get_mm_hiwater_rss(struct mm_struct *mm)
> +{
> +	return max(mm->hiwater_rss, get_mm_rss(mm));
> +}
> +
> +static inline void setmax_mm_hiwater_rss(unsigned long *maxrss,
> +					 struct mm_struct *mm)
> +{
> +	unsigned long hiwater_rss = get_mm_hiwater_rss(mm);
> +
> +	if (*maxrss < hiwater_rss)
> +		*maxrss = hiwater_rss;
> +}
> +
> +static inline unsigned long get_mm_hiwater_vm(struct mm_struct *mm)
> +{
> +	return max(mm->hiwater_vm, mm->total_vm);
> +}
> +
> +
>  /*
>   * doesn't attempt to fault and will return short.
>   */
> Index: mmotm-2.6.32-Nov24/fs/proc/task_mmu.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/fs/proc/task_mmu.c
> +++ mmotm-2.6.32-Nov24/fs/proc/task_mmu.c
> @@ -65,11 +65,11 @@ unsigned long task_vsize(struct mm_struc
>  int task_statm(struct mm_struct *mm, int *shared, int *text,
>  	       int *data, int *resident)
>  {
> -	*shared = get_mm_counter(mm, file_rss);
> +	*shared = get_mm_counter(mm, MM_FILEPAGES);
>  	*text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK))
>  								>> PAGE_SHIFT;
>  	*data = mm->total_vm - mm->shared_vm;
> -	*resident = *shared + get_mm_counter(mm, anon_rss);
> +	*resident = *shared + get_mm_counter(mm, MM_ANONPAGES);
>  	return mm->total_vm;
>  }
>  
> Index: mmotm-2.6.32-Nov24/mm/oom_kill.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/mm/oom_kill.c
> +++ mmotm-2.6.32-Nov24/mm/oom_kill.c
> @@ -400,8 +400,8 @@ static void __oom_kill_task(struct task_
>  		       "vsz:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
>  		       task_pid_nr(p), p->comm,
>  		       K(p->mm->total_vm),
> -		       K(get_mm_counter(p->mm, anon_rss)),
> -		       K(get_mm_counter(p->mm, file_rss)));
> +		       K(get_mm_counter(p->mm, MM_ANONPAGES)),
> +		       K(get_mm_counter(p->mm, MM_FILEPAGES)));
>  	task_unlock(p);
>  
>  	/*
> Index: mmotm-2.6.32-Nov24/kernel/exit.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/kernel/exit.c
> +++ mmotm-2.6.32-Nov24/kernel/exit.c
> @@ -681,6 +681,10 @@ static void exit_mm(struct task_struct *
>  	}
>  	atomic_inc(&mm->mm_count);
>  	BUG_ON(mm != tsk->active_mm);
> +	/* drop cached information */
> +	preempt_disable();
> +	sync_tsk_mm_counters();
> +	preempt_enable();

How about (get|put)_cpu in sync_tsk_mm_counters?
It disable and enable preemption.

>  	/* more a memory barrier than a real lock */
>  	task_lock(tsk);
>  	tsk->mm = NULL;
> Index: mmotm-2.6.32-Nov24/kernel/sched.c
> ===================================================================
> --- mmotm-2.6.32-Nov24.orig/kernel/sched.c
> +++ mmotm-2.6.32-Nov24/kernel/sched.c
> @@ -2858,6 +2858,7 @@ context_switch(struct rq *rq, struct tas
>  	trace_sched_switch(rq, prev, next);
>  	mm = next->mm;
>  	oldmm = prev->active_mm;
> +	prepare_mm_switch(prev, next);
>  	/*
>  	 * For paravirt, this is coupled with an exit in switch_to to
>  	 * combine the page table reload and the switch backend into
> 

I think code is not bad but I don't know how effective this patch is in practice.
Thanks for good effort. Kame. :)