* Andrea Righi <ari...@develer.com> [2010-03-01 22:23:39]:

> Infrastructure to account dirty pages per cgroup and add dirty limit
> interfaces in the cgroupfs:
> 
>  - Direct write-out: memory.dirty_ratio, memory.dirty_bytes
> 
>  - Background write-out: memory.dirty_background_ratio, 
> memory.dirty_background_bytes
> 
> Signed-off-by: Andrea Righi <ari...@develer.com>

Look good, but yet to be tested from my side.


> ---
>  include/linux/memcontrol.h |   77 ++++++++++-
>  mm/memcontrol.c            |  336 
> ++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 384 insertions(+), 29 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 1f9b119..cc88b2e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -19,12 +19,50 @@
> 
>  #ifndef _LINUX_MEMCONTROL_H
>  #define _LINUX_MEMCONTROL_H
> +
> +#include <linux/writeback.h>
>  #include <linux/cgroup.h>
> +
>  struct mem_cgroup;
>  struct page_cgroup;
>  struct page;
>  struct mm_struct;
> 
> +/* Cgroup memory statistics items exported to the kernel */
> +enum mem_cgroup_page_stat_item {
> +     MEMCG_NR_DIRTYABLE_PAGES,
> +     MEMCG_NR_RECLAIM_PAGES,
> +     MEMCG_NR_WRITEBACK,
> +     MEMCG_NR_DIRTY_WRITEBACK_PAGES,
> +};
> +
> +/*
> + * Statistics for memory cgroup.
> + */
> +enum mem_cgroup_stat_index {
> +     /*
> +      * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
> +      */
> +     MEM_CGROUP_STAT_CACHE,     /* # of pages charged as cache */
> +     MEM_CGROUP_STAT_RSS,       /* # of pages charged as anon rss */
> +     MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
> +     MEM_CGROUP_STAT_PGPGIN_COUNT,   /* # of pages paged in */
> +     MEM_CGROUP_STAT_PGPGOUT_COUNT,  /* # of pages paged out */
> +     MEM_CGROUP_STAT_EVENTS, /* sum of pagein + pageout for internal use */
> +     MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
> +     MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
> +                                     used by soft limit implementation */
> +     MEM_CGROUP_STAT_THRESHOLDS, /* decrements on each page in/out.
> +                                     used by threshold implementation */
> +     MEM_CGROUP_STAT_FILE_DIRTY,   /* # of dirty pages in page cache */
> +     MEM_CGROUP_STAT_WRITEBACK,   /* # of pages under writeback */
> +     MEM_CGROUP_STAT_WRITEBACK_TEMP,   /* # of pages under writeback using
> +                                             temporary buffers */
> +     MEM_CGROUP_STAT_UNSTABLE_NFS,   /* # of NFS unstable pages */
> +
> +     MEM_CGROUP_STAT_NSTATS,
> +};
> +
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
>  /*
>   * All "charge" functions with gfp_mask should use GFP_KERNEL or
> @@ -117,6 +155,13 @@ extern void mem_cgroup_print_oom_info(struct mem_cgroup 
> *memcg,
>  extern int do_swap_account;
>  #endif
> 
> +extern long mem_cgroup_dirty_ratio(void);
> +extern unsigned long mem_cgroup_dirty_bytes(void);
> +extern long mem_cgroup_dirty_background_ratio(void);
> +extern unsigned long mem_cgroup_dirty_background_bytes(void);
> +
> +extern s64 mem_cgroup_page_stat(enum mem_cgroup_page_stat_item item);
> +

Docstyle comments for each function would be appreciated

>  static inline bool mem_cgroup_disabled(void)
>  {
>       if (mem_cgroup_subsys.disabled)
> @@ -125,7 +170,8 @@ static inline bool mem_cgroup_disabled(void)
>  }
> 
>  extern bool mem_cgroup_oom_called(struct task_struct *task);
> -void mem_cgroup_update_file_mapped(struct page *page, int val);

Good to see you make generic use of this function

> +void mem_cgroup_update_stat(struct page *page,
> +                     enum mem_cgroup_stat_index idx, int val);
>  unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>                                               gfp_t gfp_mask, int nid,
>                                               int zid);
> @@ -300,8 +346,8 @@ mem_cgroup_print_oom_info(struct mem_cgroup *memcg, 
> struct task_struct *p)
>  {
>  }
> 
> -static inline void mem_cgroup_update_file_mapped(struct page *page,
> -                                                     int val)
> +static inline void mem_cgroup_update_stat(struct page *page,
> +                     enum mem_cgroup_stat_index idx, int val)
>  {
>  }
> 
> @@ -312,6 +358,31 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone 
> *zone, int order,
>       return 0;
>  }
> 
> +static inline long mem_cgroup_dirty_ratio(void)
> +{
> +     return vm_dirty_ratio;
> +}
> +
> +static inline unsigned long mem_cgroup_dirty_bytes(void)
> +{
> +     return vm_dirty_bytes;
> +}
> +
> +static inline long mem_cgroup_dirty_background_ratio(void)
> +{
> +     return dirty_background_ratio;
> +}
> +
> +static inline unsigned long mem_cgroup_dirty_background_bytes(void)
> +{
> +     return dirty_background_bytes;
> +}
> +
> +static inline s64 mem_cgroup_page_stat(enum mem_cgroup_page_stat_item item)
> +{
> +     return -ENOMEM;
> +}
> +
>  #endif /* CONFIG_CGROUP_MEM_CONT */
> 
>  #endif /* _LINUX_MEMCONTROL_H */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a443c30..e74cf66 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -66,31 +66,16 @@ static int really_do_swap_account __initdata = 1; /* for 
> remember boot option*/
>  #define SOFTLIMIT_EVENTS_THRESH (1000)
>  #define THRESHOLDS_EVENTS_THRESH (100)
> 
> -/*
> - * Statistics for memory cgroup.
> - */
> -enum mem_cgroup_stat_index {
> -     /*
> -      * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
> -      */
> -     MEM_CGROUP_STAT_CACHE,     /* # of pages charged as cache */
> -     MEM_CGROUP_STAT_RSS,       /* # of pages charged as anon rss */
> -     MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
> -     MEM_CGROUP_STAT_PGPGIN_COUNT,   /* # of pages paged in */
> -     MEM_CGROUP_STAT_PGPGOUT_COUNT,  /* # of pages paged out */
> -     MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
> -     MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
> -                                     used by soft limit implementation */
> -     MEM_CGROUP_STAT_THRESHOLDS, /* decrements on each page in/out.
> -                                     used by threshold implementation */
> -
> -     MEM_CGROUP_STAT_NSTATS,
> -};
> -
>  struct mem_cgroup_stat_cpu {
>       s64 count[MEM_CGROUP_STAT_NSTATS];
>  };
> 
> +/* Per cgroup page statistics */
> +struct mem_cgroup_page_stat {
> +     enum mem_cgroup_page_stat_item item;
> +     s64 value;
> +};
> +
>  /*
>   * per-zone information in memory controller.
>   */
> @@ -157,6 +142,15 @@ struct mem_cgroup_threshold_ary {
>  static bool mem_cgroup_threshold_check(struct mem_cgroup *mem);
>  static void mem_cgroup_threshold(struct mem_cgroup *mem);
> 
> +enum mem_cgroup_dirty_param {
> +     MEM_CGROUP_DIRTY_RATIO,
> +     MEM_CGROUP_DIRTY_BYTES,
> +     MEM_CGROUP_DIRTY_BACKGROUND_RATIO,
> +     MEM_CGROUP_DIRTY_BACKGROUND_BYTES,
> +
> +     MEM_CGROUP_DIRTY_NPARAMS,
> +};
> +
>  /*
>   * The memory controller data structure. The memory controller controls both
>   * page cache and RSS per cgroup. We would eventually like to provide
> @@ -205,6 +199,9 @@ struct mem_cgroup {
> 
>       unsigned int    swappiness;
> 
> +     /* control memory cgroup dirty pages */
> +     unsigned long dirty_param[MEM_CGROUP_DIRTY_NPARAMS];
> +

Could you mention what protects this field, is it the reclaim_lock?
BTW, is unsigned long sufficient to represent dirty_param(s)?

>       /* set when res.limit == memsw.limit */
>       bool            memsw_is_minimum;
> 
> @@ -1021,6 +1018,164 @@ static unsigned int get_swappiness(struct mem_cgroup 
> *memcg)
>       return swappiness;
>  }
> 
> +static unsigned long get_dirty_param(struct mem_cgroup *memcg,
> +                     enum mem_cgroup_dirty_param idx)
> +{
> +     unsigned long ret;
> +
> +     VM_BUG_ON(idx >= MEM_CGROUP_DIRTY_NPARAMS);
> +     spin_lock(&memcg->reclaim_param_lock);
> +     ret = memcg->dirty_param[idx];
> +     spin_unlock(&memcg->reclaim_param_lock);

Do we need a spinlock if we protect it using RCU? Is precise data very
important?

> +
> +     return ret;
> +}
> +
> +long mem_cgroup_dirty_ratio(void)
> +{
> +     struct mem_cgroup *memcg;
> +     long ret = vm_dirty_ratio;
> +
> +     if (mem_cgroup_disabled())
> +             return ret;
> +     /*
> +      * It's possible that "current" may be moved to other cgroup while we
> +      * access cgroup. But precise check is meaningless because the task can
> +      * be moved after our access and writeback tends to take long time.
> +      * At least, "memcg" will not be freed under rcu_read_lock().
> +      */
> +     rcu_read_lock();
> +     memcg = mem_cgroup_from_task(current);
> +     if (likely(memcg))
> +             ret = get_dirty_param(memcg, MEM_CGROUP_DIRTY_RATIO);
> +     rcu_read_unlock();
> +
> +     return ret;
> +}
> +
> +unsigned long mem_cgroup_dirty_bytes(void)
> +{
> +     struct mem_cgroup *memcg;
> +     unsigned long ret = vm_dirty_bytes;
> +
> +     if (mem_cgroup_disabled())
> +             return ret;
> +     rcu_read_lock();
> +     memcg = mem_cgroup_from_task(current);
> +     if (likely(memcg))
> +             ret = get_dirty_param(memcg, MEM_CGROUP_DIRTY_BYTES);
> +     rcu_read_unlock();
> +
> +     return ret;
> +}
> +
> +long mem_cgroup_dirty_background_ratio(void)
> +{
> +     struct mem_cgroup *memcg;
> +     long ret = dirty_background_ratio;
> +
> +     if (mem_cgroup_disabled())
> +             return ret;
> +     rcu_read_lock();
> +     memcg = mem_cgroup_from_task(current);
> +     if (likely(memcg))
> +             ret = get_dirty_param(memcg, MEM_CGROUP_DIRTY_BACKGROUND_RATIO);
> +     rcu_read_unlock();
> +
> +     return ret;
> +}
> +
> +unsigned long mem_cgroup_dirty_background_bytes(void)
> +{
> +     struct mem_cgroup *memcg;
> +     unsigned long ret = dirty_background_bytes;
> +
> +     if (mem_cgroup_disabled())
> +             return ret;
> +     rcu_read_lock();
> +     memcg = mem_cgroup_from_task(current);
> +     if (likely(memcg))
> +             ret = get_dirty_param(memcg, MEM_CGROUP_DIRTY_BACKGROUND_BYTES);
> +     rcu_read_unlock();
> +
> +     return ret;
> +}
> +
> +static inline bool mem_cgroup_can_swap(struct mem_cgroup *memcg)
> +{
> +     return do_swap_account ?
> +                     res_counter_read_u64(&memcg->memsw, RES_LIMIT) :

Shouldn't you do a res_counter_read_u64(...) > 0 for readability?
What happens if memcg->res, RES_LIMIT == memcg->memsw, RES_LIMIT?

> +                     nr_swap_pages > 0;
> +}
> +
> +static s64 mem_cgroup_get_local_page_stat(struct mem_cgroup *memcg,
> +                             enum mem_cgroup_page_stat_item item)
> +{
> +     s64 ret;
> +
> +     switch (item) {
> +     case MEMCG_NR_DIRTYABLE_PAGES:
> +             ret = res_counter_read_u64(&memcg->res, RES_LIMIT) -
> +                     res_counter_read_u64(&memcg->res, RES_USAGE);
> +             /* Translate free memory in pages */
> +             ret >>= PAGE_SHIFT;
> +             ret += mem_cgroup_read_stat(memcg, LRU_ACTIVE_FILE) +
> +                     mem_cgroup_read_stat(memcg, LRU_INACTIVE_FILE);
> +             if (mem_cgroup_can_swap(memcg))
> +                     ret += mem_cgroup_read_stat(memcg, LRU_ACTIVE_ANON) +
> +                             mem_cgroup_read_stat(memcg, LRU_INACTIVE_ANON);
> +             break;
> +     case MEMCG_NR_RECLAIM_PAGES:
> +             ret = mem_cgroup_read_stat(memcg, MEM_CGROUP_STAT_FILE_DIRTY) +
> +                     mem_cgroup_read_stat(memcg,
> +                                     MEM_CGROUP_STAT_UNSTABLE_NFS);
> +             break;
> +     case MEMCG_NR_WRITEBACK:
> +             ret = mem_cgroup_read_stat(memcg, MEM_CGROUP_STAT_WRITEBACK);
> +             break;
> +     case MEMCG_NR_DIRTY_WRITEBACK_PAGES:
> +             ret = mem_cgroup_read_stat(memcg, MEM_CGROUP_STAT_WRITEBACK) +
> +                     mem_cgroup_read_stat(memcg,
> +                             MEM_CGROUP_STAT_UNSTABLE_NFS);
> +             break;
> +     default:
> +             ret = 0;
> +             WARN_ON_ONCE(1);
> +     }
> +     return ret;
> +}
> +
> +static int mem_cgroup_page_stat_cb(struct mem_cgroup *mem, void *data)
> +{
> +     struct mem_cgroup_page_stat *stat = (struct mem_cgroup_page_stat *)data;
> +
> +     stat->value += mem_cgroup_get_local_page_stat(mem, stat->item);
> +     return 0;
> +}
> +
> +s64 mem_cgroup_page_stat(enum mem_cgroup_page_stat_item item)
> +{
> +     struct mem_cgroup_page_stat stat = {};
> +     struct mem_cgroup *memcg;
> +
> +     if (mem_cgroup_disabled())
> +             return -ENOMEM;
> +     rcu_read_lock();
> +     memcg = mem_cgroup_from_task(current);
> +     if (memcg) {
> +             /*
> +              * Recursively evaulate page statistics against all cgroup
> +              * under hierarchy tree
> +              */
> +             stat.item = item;
> +             mem_cgroup_walk_tree(memcg, &stat, mem_cgroup_page_stat_cb);
> +     } else
> +             stat.value = -ENOMEM;
> +     rcu_read_unlock();
> +
> +     return stat.value;
> +}
> +
>  static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
>  {
>       int *val = data;
> @@ -1263,14 +1418,16 @@ static void record_last_oom(struct mem_cgroup *mem)
>  }
> 
>  /*
> - * Currently used to update mapped file statistics, but the routine can be
> - * generalized to update other statistics as well.
> + * Generalized routine to update memory cgroup statistics.
>   */
> -void mem_cgroup_update_file_mapped(struct page *page, int val)
> +void mem_cgroup_update_stat(struct page *page,
> +                     enum mem_cgroup_stat_index idx, int val)
>  {
>       struct mem_cgroup *mem;
>       struct page_cgroup *pc;
> 
> +     if (mem_cgroup_disabled())
> +             return;
>       pc = lookup_page_cgroup(page);
>       if (unlikely(!pc))
>               return;
> @@ -1286,7 +1443,8 @@ void mem_cgroup_update_file_mapped(struct page *page, 
> int val)
>       /*
>        * Preemption is already disabled. We can use __this_cpu_xxx
>        */
> -     __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED], val);
> +     VM_BUG_ON(idx >= MEM_CGROUP_STAT_NSTATS);
> +     __this_cpu_add(mem->stat->count[idx], val);
> 
>  done:
>       unlock_page_cgroup(pc);
> @@ -3033,6 +3191,10 @@ enum {
>       MCS_PGPGIN,
>       MCS_PGPGOUT,
>       MCS_SWAP,
> +     MCS_FILE_DIRTY,
> +     MCS_WRITEBACK,
> +     MCS_WRITEBACK_TEMP,
> +     MCS_UNSTABLE_NFS,
>       MCS_INACTIVE_ANON,
>       MCS_ACTIVE_ANON,
>       MCS_INACTIVE_FILE,
> @@ -3055,6 +3217,10 @@ struct {
>       {"pgpgin", "total_pgpgin"},
>       {"pgpgout", "total_pgpgout"},
>       {"swap", "total_swap"},
> +     {"filedirty", "dirty_pages"},
> +     {"writeback", "writeback_pages"},
> +     {"writeback_tmp", "writeback_temp_pages"},
> +     {"nfs", "nfs_unstable"},
>       {"inactive_anon", "total_inactive_anon"},
>       {"active_anon", "total_active_anon"},
>       {"inactive_file", "total_inactive_file"},
> @@ -3083,6 +3249,14 @@ static int mem_cgroup_get_local_stat(struct mem_cgroup 
> *mem, void *data)
>               val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_SWAPOUT);
>               s->stat[MCS_SWAP] += val * PAGE_SIZE;
>       }
> +     val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_FILE_DIRTY);
> +     s->stat[MCS_FILE_DIRTY] += val;
> +     val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_WRITEBACK);
> +     s->stat[MCS_WRITEBACK] += val;
> +     val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_WRITEBACK_TEMP);
> +     s->stat[MCS_WRITEBACK_TEMP] += val;
> +     val = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_UNSTABLE_NFS);
> +     s->stat[MCS_UNSTABLE_NFS] += val;
> 
>       /* per zone stat */
>       val = mem_cgroup_get_local_zonestat(mem, LRU_INACTIVE_ANON);
> @@ -3467,6 +3641,50 @@ unlock:
>       return ret;
>  }
> 
> +static u64 mem_cgroup_dirty_read(struct cgroup *cgrp, struct cftype *cft)
> +{
> +     struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +     int type = cft->private;
> +
> +     return get_dirty_param(memcg, type);
> +}
> +
> +static int
> +mem_cgroup_dirty_write(struct cgroup *cgrp, struct cftype *cft, u64 val)
> +{
> +     struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> +     int type = cft->private;
> +
> +     if (cgrp->parent == NULL)
> +             return -EINVAL;
> +     if (((type == MEM_CGROUP_DIRTY_RATIO) ||
> +             (type == MEM_CGROUP_DIRTY_BACKGROUND_RATIO)) && (val > 100))
> +             return -EINVAL;
> +
> +     spin_lock(&memcg->reclaim_param_lock);
> +     switch (type) {
> +     case MEM_CGROUP_DIRTY_RATIO:
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_RATIO] = val;
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BYTES] = 0;
> +             break;
> +     case MEM_CGROUP_DIRTY_BYTES:
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_RATIO] = 0;
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BYTES] = val;
> +             break;
> +     case MEM_CGROUP_DIRTY_BACKGROUND_RATIO:
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_RATIO] = val;
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_BYTES] = 0;
> +             break;
> +     case MEM_CGROUP_DIRTY_BACKGROUND_BYTES:
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_RATIO] = 0;
> +             memcg->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_BYTES] = val;
> +             break;
> +     }
> +     spin_unlock(&memcg->reclaim_param_lock);
> +
> +     return 0;
> +}
> +
>  static struct cftype mem_cgroup_files[] = {
>       {
>               .name = "usage_in_bytes",
> @@ -3518,6 +3736,30 @@ static struct cftype mem_cgroup_files[] = {
>               .write_u64 = mem_cgroup_swappiness_write,
>       },
>       {
> +             .name = "dirty_ratio",
> +             .read_u64 = mem_cgroup_dirty_read,
> +             .write_u64 = mem_cgroup_dirty_write,
> +             .private = MEM_CGROUP_DIRTY_RATIO,
> +     },
> +     {
> +             .name = "dirty_bytes",
> +             .read_u64 = mem_cgroup_dirty_read,
> +             .write_u64 = mem_cgroup_dirty_write,
> +             .private = MEM_CGROUP_DIRTY_BYTES,
> +     },
> +     {
> +             .name = "dirty_background_ratio",
> +             .read_u64 = mem_cgroup_dirty_read,
> +             .write_u64 = mem_cgroup_dirty_write,
> +             .private = MEM_CGROUP_DIRTY_BACKGROUND_RATIO,
> +     },
> +     {
> +             .name = "dirty_background_bytes",
> +             .read_u64 = mem_cgroup_dirty_read,
> +             .write_u64 = mem_cgroup_dirty_write,
> +             .private = MEM_CGROUP_DIRTY_BACKGROUND_BYTES,
> +     },
> +     {
>               .name = "move_charge_at_immigrate",
>               .read_u64 = mem_cgroup_move_charge_read,
>               .write_u64 = mem_cgroup_move_charge_write,
> @@ -3725,6 +3967,19 @@ static int mem_cgroup_soft_limit_tree_init(void)
>       return 0;
>  }
> 
> +/*
> + * NOTE: called only with &src->reclaim_param_lock held from
> + * mem_cgroup_create().
> + */
> +static inline void
> +copy_dirty_params(struct mem_cgroup *dst, struct mem_cgroup *src)
> +{
> +     int i;
> +
> +     for (i = 0; i < MEM_CGROUP_DIRTY_NPARAMS; i++)
> +             dst->dirty_param[i] = src->dirty_param[i];
> +}
> +
>  static struct cgroup_subsys_state * __ref
>  mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>  {
> @@ -3776,8 +4031,37 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct 
> cgroup *cont)
>       mem->last_scanned_child = 0;
>       spin_lock_init(&mem->reclaim_param_lock);
> 
> -     if (parent)
> +     if (parent) {
>               mem->swappiness = get_swappiness(parent);
> +
> +             spin_lock(&parent->reclaim_param_lock);
> +             copy_dirty_params(mem, parent);
> +             spin_unlock(&parent->reclaim_param_lock);
> +     } else {
> +             /*
> +              * XXX: should we need a lock here? we could switch from
> +              * vm_dirty_ratio to vm_dirty_bytes or vice versa but we're not
> +              * reading them atomically. The same for dirty_background_ratio
> +              * and dirty_background_bytes.
> +              *
> +              * For now, try to read them speculatively and retry if a
> +              * "conflict" is detected.a

The do while loop is subtle, can we add a validate check,share it with
the write routine and retry if validation fails?

> +              */
> +             do {
> +                     mem->dirty_param[MEM_CGROUP_DIRTY_RATIO] =
> +                                             vm_dirty_ratio;
> +                     mem->dirty_param[MEM_CGROUP_DIRTY_BYTES] =
> +                                             vm_dirty_bytes;
> +             } while (mem->dirty_param[MEM_CGROUP_DIRTY_RATIO] &&
> +                      mem->dirty_param[MEM_CGROUP_DIRTY_BYTES]);
> +             do {
> +                     mem->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_RATIO] =
> +                                             dirty_background_ratio;
> +                     mem->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_BYTES] =
> +                                             dirty_background_bytes;
> +             } while (mem->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_RATIO] &&
> +                     mem->dirty_param[MEM_CGROUP_DIRTY_BACKGROUND_BYTES]);
> +     }
>       atomic_set(&mem->refcnt, 1);
>       mem->move_charge_at_immigrate = 0;
>       mutex_init(&mem->thresholds_lock);
> -- 
> 1.6.3.3
> 

-- 
        Three Cheers,
        Balbir
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