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    SubjectRe: [PATCH -mmotm 2/3] memcg: dirty pages accounting and limiting infrastructure
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    On Mon, Mar 1, 2010 at 11:23 PM, Andrea Righi <arighi@develer.com> wrote:
    > 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 <arighi@develer.com>
    > ---
    >  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);
    > +
    >  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);
    > +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;

    Why ENOMEM? Probably, EINVAL or ENOSYS?

    > +}
    > +
    >  #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];
    > +
    >        /* 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);
    > +
    > +       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) :
    > +                       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);

    I think it's a bug, not warning.

    > +       }
    > +       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;

    EINVAL/ENOSYS?

    > +       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;

    ditto.

    > +       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)

    EXPORT_SYMBOL_GPL(mem_cgroup_update_stat) is needed, since
    it uses by filesystems.

    >  {
    >        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))

    Too many unnecessary brackets

    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.
    > +                */
    > +               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
    >
    >
    --
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