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    SubjectRe: [PATCH v5 2/6] memcg: stop vmscan when enough done.
    On Thu 18-08-11 15:42:59, KAMEZAWA Hiroyuki wrote:
    > On Thu, 18 Aug 2011 08:27:22 +0200
    > Michal Hocko <mhocko@suse.cz> wrote:
    >
    > > On Thu 18-08-11 08:52:33, KAMEZAWA Hiroyuki wrote:
    > > > On Wed, 17 Aug 2011 13:35:50 +0200
    > > > Michal Hocko <mhocko@suse.cz> wrote:
    > > >
    > > > > On Wed 17-08-11 09:54:05, KAMEZAWA Hiroyuki wrote:
    > > > > > On Thu, 11 Aug 2011 16:50:55 +0200
    > > > > > > - mem_cgroup_force_empty asks for reclaiming all pages. I guess it should be
    > > > > > > OK but will have to think about it some more.
    > > > > >
    > > > > > force_empty/rmdir() is allowed to be stopped by Ctrl-C. I think passing res->usage
    > > > > > is overkilling.
    > > > >
    > > > > So, how many pages should be reclaimed then?
    > > > >
    > > >
    > > > How about (1 << (MAX_ORDER-1))/loop ?
    > >
    > > Hmm, I am not sure I see any benefit. We want to reclaim all those
    > > pages why shouldn't we do it in one batch? If we use a value based on
    > > MAX_ORDER then we make a bigger chance that force_empty fails for big
    > > cgroups (e.g. with a lot of page cache).
    >
    > Why bigger chance to fail ? retry counter is decreased only when we cannot
    > make any reclaim. The number passed here is not problem against the faiulre.

    Yes, you are right. I have overlooked that.


    > I don't like very long vmscan which cannot be stopped by Ctrl-C.

    Sure, now I see your point. Thanks for clarification.

    > > Anyway, if we want to mimic the previous behavior then we should use
    > > something like nr_nodes * SWAP_CLUSTER_MAX (the above value would be
    > > sufficient for up to 32 nodes).
    > >
    >
    > agreed.

    Updated patch:
    Changes since v1:
    - reclaim nr_nodes * SWAP_CLUSTER_MAX in mem_cgroup_force_empty
    ---
    From: Michal Hocko <mhocko@suse.cz>
    Subject: memcg: add nr_pages argument for hierarchical reclaim

    Now that we are doing memcg direct reclaim limited to nr_to_reclaim
    pages (introduced by "memcg: stop vmscan when enough done.") we have to
    be more careful. Currently we are using SWAP_CLUSTER_MAX which is OK for
    most callers but it might cause failures for limit resize or force_empty
    code paths on big NUMA machines.

    Previously we might have reclaimed up to nr_nodes * SWAP_CLUSTER_MAX
    while now we have it at SWAP_CLUSTER_MAX. Both resize and force_empty rely
    on reclaiming a certain amount of pages and retrying if their condition is
    still not met.

    Let's add nr_pages argument to mem_cgroup_hierarchical_reclaim which will
    push it further to try_to_free_mem_cgroup_pages. We still fall back to
    SWAP_CLUSTER_MAX for small requests so the standard code (hot) paths are not
    affected by this.

    We have to be careful in mem_cgroup_do_charge and do not provide the
    given nr_pages because we would reclaim too much for THP which can
    safely fall back to single page allocations.

    mem_cgroup_force_empty could try to reclaim all pages at once but it is much
    better to limit the nr_pages to something reasonable so that we are able to
    terminate it by a signal. Let's mimic previous behavior by asking for
    MAX_NUMNODES * SWAP_CLUSTER_MAX.

    Signed-off-by: Michal Hocko <mhocko@suse.cz>

    Index: linus_tree/include/linux/memcontrol.h
    ===================================================================
    --- linus_tree.orig/include/linux/memcontrol.h 2011-08-18 09:30:24.000000000 +0200
    +++ linus_tree/include/linux/memcontrol.h 2011-08-18 09:30:36.000000000 +0200
    @@ -130,7 +130,8 @@ extern void mem_cgroup_print_oom_info(st

    extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
    gfp_t gfp_mask, bool noswap,
    - struct memcg_scanrecord *rec);
    + struct memcg_scanrecord *rec,
    + unsigned long nr_pages);
    extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
    gfp_t gfp_mask, bool noswap,
    struct zone *zone,
    Index: linus_tree/mm/memcontrol.c
    ===================================================================
    --- linus_tree.orig/mm/memcontrol.c 2011-08-18 09:30:34.000000000 +0200
    +++ linus_tree/mm/memcontrol.c 2011-08-18 09:36:41.000000000 +0200
    @@ -1729,12 +1729,15 @@ static void mem_cgroup_record_scanstat(s
    * (other groups can be removed while we're walking....)
    *
    * If shrink==true, for avoiding to free too much, this returns immedieately.
    + * Given nr_pages tells how many pages are we over the soft limit or how many
    + * pages do we want to reclaim in the direct reclaim mode.
    */
    static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
    struct zone *zone,
    gfp_t gfp_mask,
    unsigned long reclaim_options,
    - unsigned long *total_scanned)
    + unsigned long *total_scanned,
    + unsigned long nr_pages)
    {
    struct mem_cgroup *victim;
    int ret, total = 0;
    @@ -1743,11 +1746,8 @@ static int mem_cgroup_hierarchical_recla
    bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
    bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
    struct memcg_scanrecord rec;
    - unsigned long excess;
    unsigned long scanned;

    - excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
    -
    /* If memsw_is_minimum==1, swap-out is of-no-use. */
    if (!check_soft && !shrink && root_mem->memsw_is_minimum)
    noswap = true;
    @@ -1785,11 +1785,11 @@ static int mem_cgroup_hierarchical_recla
    }
    /*
    * We want to do more targeted reclaim.
    - * excess >> 2 is not to excessive so as to
    + * nr_pages >> 2 is not to excessive so as to
    * reclaim too much, nor too less that we keep
    * coming back to reclaim from this cgroup
    */
    - if (total >= (excess >> 2) ||
    + if (total >= (nr_pages >> 2) ||
    (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
    css_put(&victim->css);
    break;
    @@ -1816,7 +1816,7 @@ static int mem_cgroup_hierarchical_recla
    *total_scanned += scanned;
    } else
    ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
    - noswap, &rec);
    + noswap, &rec, nr_pages);
    mem_cgroup_record_scanstat(&rec);
    css_put(&victim->css);
    /*
    @@ -2331,8 +2331,14 @@ static int mem_cgroup_do_charge(struct m
    if (!(gfp_mask & __GFP_WAIT))
    return CHARGE_WOULDBLOCK;

    + /*
    + * We are lying about nr_pages because we do not want to
    + * reclaim too much for THP pages which should rather fallback
    + * to small pages.
    + */
    ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
    - gfp_mask, flags, NULL);
    + gfp_mask, flags, NULL,
    + 1);
    if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
    return CHARGE_RETRY;
    /*
    @@ -3567,7 +3573,8 @@ static int mem_cgroup_resize_limit(struc

    mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
    MEM_CGROUP_RECLAIM_SHRINK,
    - NULL);
    + NULL,
    + (val-memlimit) >> PAGE_SHIFT);
    curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
    /* Usage is reduced ? */
    if (curusage >= oldusage)
    @@ -3628,7 +3635,8 @@ static int mem_cgroup_resize_memsw_limit
    mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
    MEM_CGROUP_RECLAIM_NOSWAP |
    MEM_CGROUP_RECLAIM_SHRINK,
    - NULL);
    + NULL,
    + (val-memswlimit) >> PAGE_SHIFT);
    curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
    /* Usage is reduced ? */
    if (curusage >= oldusage)
    @@ -3671,10 +3679,12 @@ unsigned long mem_cgroup_soft_limit_recl
    break;

    nr_scanned = 0;
    + excess = res_counter_soft_limit_excess(&mz->mem->res);
    reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
    gfp_mask,
    MEM_CGROUP_RECLAIM_SOFT,
    - &nr_scanned);
    + &nr_scanned,
    + excess >> PAGE_SHIFT);
    nr_reclaimed += reclaimed;
    *total_scanned += nr_scanned;
    spin_lock(&mctz->lock);
    @@ -3870,8 +3880,10 @@ try_to_free:
    rec.context = SCAN_BY_SHRINK;
    rec.mem = mem;
    rec.root = mem;
    + /* reclaim from every node at least something */
    progress = try_to_free_mem_cgroup_pages(mem, GFP_KERNEL,
    - false, &rec);
    + false, &rec,
    + MAX_NUMNODES * SWAP_CLUSTER_MAX);
    if (!progress) {
    nr_retries--;
    /* maybe some writeback is necessary */
    Index: linus_tree/mm/vmscan.c
    ===================================================================
    --- linus_tree.orig/mm/vmscan.c 2011-08-18 09:30:24.000000000 +0200
    +++ linus_tree/mm/vmscan.c 2011-08-18 09:30:36.000000000 +0200
    @@ -2340,7 +2340,8 @@ unsigned long mem_cgroup_shrink_node_zon
    unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    gfp_t gfp_mask,
    bool noswap,
    - struct memcg_scanrecord *rec)
    + struct memcg_scanrecord *rec,
    + unsigned long nr_pages)
    {
    struct zonelist *zonelist;
    unsigned long nr_reclaimed;
    @@ -2350,7 +2351,7 @@ unsigned long try_to_free_mem_cgroup_pag
    .may_writepage = !laptop_mode,
    .may_unmap = 1,
    .may_swap = !noswap,
    - .nr_to_reclaim = SWAP_CLUSTER_MAX,
    + .nr_to_reclaim = max_t(unsigned long, nr_pages, SWAP_CLUSTER_MAX),
    .order = 0,
    .mem_cgroup = mem_cont,
    .memcg_record = rec,
    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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