Re: [PATCH V7 7/9] Per-memcg background reclaim.

[Ying Han <yinghan@google.com>]

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On Thu, Apr 21, 2011 at 11:00 PM, KOSAKI Motohiro <
kosaki.motohiro@jp.fujitsu.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.
> >
> > changelog v7..v6:
> > 1. change based on KAMAZAWA's patchset. Each memcg reclaims now reclaims
> > SWAP_CLUSTER_MAX of pages and putback the memcg to the tail of list.
> > memcg-kswapd will visit memcgs in round-robin manner and reduce usages.
> >
> > 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>
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > ---
> >  include/linux/memcontrol.h |    9 +++
> >  mm/memcontrol.c            |   18 +++++++
> >  mm/vmscan.c                |  118
> ++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 145 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 7444738..39eade6 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 4696fd8..41eaa62 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1105,6 +1105,24 @@ 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 63c557e..ba03a10 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;
> >  };
>
> Bah!
> If you need sc.priority, you have to make cleanup patch at first. and
> all current reclaim path have to use sc.priority. Please don't increase
> unnecessary mess.
>
> hmm. so then I would change it by passing the priority
> as separate parameter.
>


>
> >
> >  #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
> > @@ -2620,10 +2624,124 @@ static void kswapd_try_to_sleep(struct kswapd
> *kswapd_p, int order,
> >       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 shrink_memcg_node(pg_data_t *pgdat, int order,
> > +                             struct scan_control *sc)
> > +{
> > +     int i;
> > +     unsigned long total_scanned = 0;
> > +     struct mem_cgroup *mem_cont = sc->mem_cgroup;
> > +     int priority = sc->priority;
>
> unnecessary local variables. we can keep smaller stack.
>
> ok.

>
> > +
> > +     /*
> > +      * 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;
>
> please make helper function for may_writepage. iow, don't cut-n-paste.
>
> hmm, can you help to clarify that?
>


> > +/*
> > + * Per cgroup background reclaim.
> > + * TODO: Take off the order since memcg always do order 0
> > + */
> > +static unsigned long shrink_mem_cgroup(struct mem_cgroup *mem_cont, int
> order)
> > +{
> > +     int i, nid, priority, 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,
>
> No. memcg has per-memcg swappiness. Please don't use global swappiness
> value.
>
> sounds reasonable, i will take a look at it.

>
> > +             .order = order,
> > +             .mem_cgroup = mem_cont,
> > +     };
> > +
> > +     do_nodes = NODE_MASK_NONE;
> > +     sc.may_writepage = !laptop_mode;
> > +     sc.nr_reclaimed = 0;
>
> this initialization move into sc static initializer. balance pgdat has
> loop_again label and this doesn't.
>

will change.


>
> > +     total_scanned = 0;
> > +
> > +     do_nodes = node_states[N_ONLINE];
>
> Why do we need care memoryless node? N_HIGH_MEMORY is wrong?
>
hmm, let me look into that.

>
> > +
> > +     for (priority = DEF_PRIORITY;
> > +             (priority >= 0) && (sc.nr_to_reclaim > sc.nr_reclaimed);
> > +             priority--) {
>
> bah. bad coding style...
>

ok. will change.

>
> > +
> > +             sc.priority = priority;
> > +             /* The swap token gets in the way of swapout... */
> > +             if (!priority)
> > +                     disable_swap_token();
>
> Why?
>
> disable swap token mean "Please devest swap preventation privilege from
> owner task. Instead we endure swap storm and performance hit".
> However I doublt memcg memory shortage is good situation to make swap
> storm.
>

I am not sure about that either way. we probably can leave as it is and make
corresponding change if real problem is observed?

>
>
> > +
> > +             for (loop = num_online_nodes();
> > +                     (loop > 0) && !nodes_empty(do_nodes);
> > +                     loop--) {
>
> Why don't you use for_each_online_node()?
> Maybe for_each_node_state(n, N_HIGH_MEMORY) is best option?
>
> At least, find_next_bit() is efficient than bare loop?
>



> > +
> > +                     nid = mem_cgroup_select_victim_node(mem_cont,
> > +                                                     &do_nodes);
> > +
> > +                     pgdat = NODE_DATA(nid);
> > +                     shrink_memcg_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))
> > +                                     break;
> > +                     }
>
> memory less node check is here. but we can check it before.
>

Not sure I understand this, can you help to clarify?

thank you for reviewing

--Ying

>
> > +                     if (i < 0)
> > +                             node_clear(nid, do_nodes);
> > +
> > +                     if (mem_cgroup_watermark_ok(mem_cont,
> > +                                             CHARGE_WMARK_HIGH))
> > +                             goto out;
> > +             }
> > +
> > +             if (total_scanned && priority < DEF_PRIORITY - 2)
> > +                     congestion_wait(WRITE, HZ/10);
> > +     }
> > +out:
> > +     return sc.nr_reclaimed;
> > +}
> > +#else
> >  static unsigned long shrink_mem_cgroup(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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