Re: [PATCH V6 06/10] Per-memcg background reclaim.

[Ying Han <yinghan@google.com>]

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On Tue, Apr 19, 2011 at 6:03 PM, KAMEZAWA Hiroyuki <
kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Mon, 18 Apr 2011 20:57:42 -0700
> Ying Han <yinghan@google.com> wrote:
>
> > This is the main loop of per-memcg background reclaim which is
> implemented in
> > function balance_mem_cgroup_pgdat().
> >
> > The function performs a priority loop similar to global reclaim. During
> each
> > iteration it invokes balance_pgdat_node() for all nodes on the system,
> which
> > is another new function performs background reclaim per node. After
> reclaiming
> > each node, it checks mem_cgroup_watermark_ok() and breaks the priority
> loop if
> > it returns true.
> >
>
> Seems getting better. But some comments, below.
>

thank you for reviewing.

>
>
> > changelog v6..v5:
> > 1. add mem_cgroup_zone_reclaimable_pages()
> > 2. fix some comment style.
> >
> > changelog v5..v4:
> > 1. remove duplicate check on nodes_empty()
> > 2. add logic to check if the per-memcg lru is empty on the zone.
> >
> > changelog v4..v3:
> > 1. split the select_victim_node and zone_unreclaimable to a seperate
> patches
> > 2. remove the logic tries to do zone balancing.
> >
> > changelog v3..v2:
> > 1. change mz->all_unreclaimable to be boolean.
> > 2. define ZONE_RECLAIMABLE_RATE macro shared by zone and per-memcg
> reclaim.
> > 3. some more clean-up.
> >
> > changelog v2..v1:
> > 1. move the per-memcg per-zone clear_unreclaimable into uncharge stage.
> > 2. shared the kswapd_run/kswapd_stop for per-memcg and global background
> > reclaim.
> > 3. name the per-memcg memcg as "memcg-id" (css->id). And the global
> kswapd
> > keeps the same name.
> > 4. fix a race on kswapd_stop while the per-memcg-per-zone info could be
> accessed
> > after freeing.
> > 5. add the fairness in zonelist where memcg remember the last zone
> reclaimed
> > from.
> >
> > Signed-off-by: Ying Han <yinghan@google.com>
> > ---
> >  include/linux/memcontrol.h |    9 +++
> >  mm/memcontrol.c            |   18 +++++
> >  mm/vmscan.c                |  151
> ++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 178 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index d4ff7f2..a4747b0 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -115,6 +115,8 @@ extern void mem_cgroup_end_migration(struct
> mem_cgroup *mem,
> >   */
> >  int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg);
> >  int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg);
> > +unsigned long mem_cgroup_zone_reclaimable_pages(struct mem_cgroup
> *memcg,
> > +                                               struct zone *zone);
> >  unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
> >                                      struct zone *zone,
> >                                      enum lru_list lru);
> > @@ -311,6 +313,13 @@ mem_cgroup_inactive_file_is_low(struct mem_cgroup
> *memcg)
> >  }
> >
> >  static inline unsigned long
> > +mem_cgroup_zone_reclaimable_pages(struct mem_cgroup *memcg,
> > +                                 struct zone *zone)
> > +{
> > +     return 0;
> > +}
> > +
> > +static inline unsigned long
> >  mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg, struct zone *zone,
> >                        enum lru_list lru)
> >  {
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 06fddd2..7490147 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1097,6 +1097,24 @@ int mem_cgroup_inactive_file_is_low(struct
> mem_cgroup *memcg)
> >       return (active > inactive);
> >  }
> >
> > +unsigned long mem_cgroup_zone_reclaimable_pages(struct mem_cgroup
> *memcg,
> > +                                             struct zone *zone)
> > +{
> > +     int nr;
> > +     int nid = zone_to_nid(zone);
> > +     int zid = zone_idx(zone);
> > +     struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid,
> zid);
> > +
> > +     nr = MEM_CGROUP_ZSTAT(mz, NR_ACTIVE_FILE) +
> > +          MEM_CGROUP_ZSTAT(mz, NR_INACTIVE_FILE);
> > +
> > +     if (nr_swap_pages > 0)
> > +             nr += MEM_CGROUP_ZSTAT(mz, NR_ACTIVE_ANON) +
> > +                   MEM_CGROUP_ZSTAT(mz, NR_INACTIVE_ANON);
> > +
> > +     return nr;
> > +}
> > +
> >  unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
> >                                      struct zone *zone,
> >                                      enum lru_list lru)
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 0060d1e..2a5c734 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -47,6 +47,8 @@
> >
> >  #include <linux/swapops.h>
> >
> > +#include <linux/res_counter.h>
> > +
> >  #include "internal.h"
> >
> >  #define CREATE_TRACE_POINTS
> > @@ -111,6 +113,8 @@ struct scan_control {
> >        * are scanned.
> >        */
> >       nodemask_t      *nodemask;
> > +
> > +     int priority;
> >  };
> >
> >  #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
> > @@ -2625,11 +2629,158 @@ out:
> >       finish_wait(wait_h, &wait);
> >  }
> >
> > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > +/*
> > + * The function is used for per-memcg LRU. It scanns all the zones of
> the
> > + * node and returns the nr_scanned and nr_reclaimed.
> > + */
> > +static void balance_pgdat_node(pg_data_t *pgdat, int order,
> > +                                     struct scan_control *sc)
> > +{
>
>
> shrink_memcg_node() instead of balance_pgdat_node() ?
>
> I guess the name is misleading.
>

ok. will make the change

>
> > +     int i;
> > +     unsigned long total_scanned = 0;
> > +     struct mem_cgroup *mem_cont = sc->mem_cgroup;
> > +     int priority = sc->priority;
> > +
> > +     /*
> > +      * This dma->highmem order is consistant with global reclaim.
> > +      * We do this because the page allocator works in the opposite
> > +      * direction although memcg user pages are mostly allocated at
> > +      * highmem.
> > +      */
> > +     for (i = 0; i < pgdat->nr_zones; i++) {
> > +             struct zone *zone = pgdat->node_zones + i;
> > +             unsigned long scan = 0;
> > +
> > +             scan = mem_cgroup_zone_reclaimable_pages(mem_cont, zone);
> > +             if (!scan)
> > +                     continue;
> > +
> > +             sc->nr_scanned = 0;
> > +             shrink_zone(priority, zone, sc);
> > +             total_scanned += sc->nr_scanned;
> > +
> > +             /*
> > +              * If we've done a decent amount of scanning and
> > +              * the reclaim ratio is low, start doing writepage
> > +              * even in laptop mode
> > +              */
> > +             if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
> > +                 total_scanned > sc->nr_reclaimed + sc->nr_reclaimed /
> 2) {
> > +                     sc->may_writepage = 1;
> > +             }
> > +     }
> > +
> > +     sc->nr_scanned = total_scanned;
> > +}
> > +
> > +/*
> > + * Per cgroup background reclaim.
> > + * TODO: Take off the order since memcg always do order 0
> > + */
> > +static unsigned long balance_mem_cgroup_pgdat(struct mem_cgroup
> *mem_cont,
> > +                                           int order)
>
> Here, too. shrink_mem_cgroup() may be straightforward.
>

will make the change.

>
>
> > +{
> > +     int i, nid;
> > +     int start_node;
> > +     int priority;
> > +     bool wmark_ok;
> > +     int loop;
> > +     pg_data_t *pgdat;
> > +     nodemask_t do_nodes;
> > +     unsigned long total_scanned;
> > +     struct scan_control sc = {
> > +             .gfp_mask = GFP_KERNEL,
> > +             .may_unmap = 1,
> > +             .may_swap = 1,
> > +             .nr_to_reclaim = SWAP_CLUSTER_MAX,
> > +             .swappiness = vm_swappiness,
> > +             .order = order,
> > +             .mem_cgroup = mem_cont,
> > +     };
> > +
> > +loop_again:
> > +     do_nodes = NODE_MASK_NONE;
> > +     sc.may_writepage = !laptop_mode;
>
> Even with !laptop_mode, "write_page since the 1st scan" should be avoided.
> How about sc.may_writepage = 1 when we do "goto loop_again;" ?
>
> sounds a safe change to make. will add it.
>


> > +     sc.nr_reclaimed = 0;
> > +     total_scanned = 0;
> > +
> > +     for (priority = DEF_PRIORITY; priority >= 0; priority--) {
> > +             sc.priority = priority;
> > +             wmark_ok = false;
> > +             loop = 0;
> > +
> > +             /* The swap token gets in the way of swapout... */
> > +             if (!priority)
> > +                     disable_swap_token();
> > +
> > +             if (priority == DEF_PRIORITY)
> > +                     do_nodes = node_states[N_ONLINE];
>
> This can be moved out from the loop.
>
> ok. changed.

> > +
> > +             while (1) {
> > +                     nid = mem_cgroup_select_victim_node(mem_cont,
> > +                                                     &do_nodes);
> > +
> > +                     /*
> > +                      * Indicate we have cycled the nodelist once
> > +                      * TODO: we might add MAX_RECLAIM_LOOP for
> preventing
> > +                      * kswapd burning cpu cycles.
> > +                      */
> > +                     if (loop == 0) {
> > +                             start_node = nid;
> > +                             loop++;
> > +                     } else if (nid == start_node)
> > +                             break;
> > +
>
> Hmm...let me try a different style.
> ==
>        start_node = mem_cgroup_select_victim_node(mem_cont, &do_nodes);
>        for (nid = start_node;
>             nid != start_node && !node_empty(do_nodes);
>             nid = mem_cgroup_select_victim_node(mem_cont, &do_nodes)) {
>
>                shrink_memcg_node(NODE_DATA(nid), order, &sc);
>                 total_scanned += sc.nr_scanned;
>                 for (i = 0; i < NODE_DATA(nid)->nr_zones; i++) {
>                        if (populated_zone(NODE_DATA(nid)->node_zones + i))
>                                break;
>                }
>                if (i == NODE_DATA(nid)->nr_zones)
>                         node_clear(nid, do_nodes);
>                if (mem_cgroup_watermark_ok(mem_cont, CHARGE_WMARK_HIGH))
>                         break;
>        }
> ==
>
> In short, I like for() loop rather than while(1) because next calculation
> and
> end condition are clear.
>

Ok. I should be able to make that change.

>
>
>
> > +                     pgdat = NODE_DATA(nid);
> > +                     balance_pgdat_node(pgdat, order, &sc);
> > +                     total_scanned += sc.nr_scanned;
> > +
> > +                     for (i = pgdat->nr_zones - 1; i >= 0; i--) {
> > +                             struct zone *zone = pgdat->node_zones + i;
> > +
> > +                             if (!populated_zone(zone))
> > +                                     continue;
> > +                     }
> > +                     if (i < 0)
> > +                             node_clear(nid, do_nodes);
> Isn't this wrong ? I guess
>                if (populated_zone(zone))
>                        break;
> is what you want to do.
>
> hmm. you are right.

--Ying

--Ying

> Thanks,
> -Kame
> > +
> > +                     if (mem_cgroup_watermark_ok(mem_cont,
> > +                                                     CHARGE_WMARK_HIGH))
> {
> > +                             wmark_ok = true;
> > +                             goto out;
> > +                     }
> > +
> > +                     if (nodes_empty(do_nodes)) {
> > +                             wmark_ok = true;
> > +                             goto out;
> > +                     }
> > +             }
> > +
> > +             if (total_scanned && priority < DEF_PRIORITY - 2)
> > +                     congestion_wait(WRITE, HZ/10);
> > +
> > +             if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
> > +                     break;
> > +     }
> > +out:
> > +     if (!wmark_ok) {
> > +             cond_resched();
> > +
> > +             try_to_freeze();
> > +
> > +             goto loop_again;
> > +     }
> > +
> > +     return sc.nr_reclaimed;
> > +}
> > +#else
> >  static unsigned long balance_mem_cgroup_pgdat(struct mem_cgroup
> *mem_cont,
> >                                                       int order)
> >  {
> >       return 0;
> >  }
> > +#endif
> >
> >  /*
> >   * The background pageout daemon, started as a kernel thread
> > --
> > 1.7.3.1
> >
> > --
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