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    SubjectRe: [PATCH] memory cgroup: update root memory cgroup when node is onlined
    At 09/14/2012 09:36 AM, Hugh Dickins Wrote:
    > On Thu, 13 Sep 2012, Johannes Weiner wrote:
    >> On Thu, Sep 13, 2012 at 03:14:28PM +0800, Wen Congyang wrote:
    >>> root_mem_cgroup->info.nodeinfo is initialized when the system boots.
    >>> But NODE_DATA(nid) is null if the node is not onlined, so
    >>> root_mem_cgroup->info.nodeinfo[nid]->zoneinfo[zone].lruvec.zone contains
    >>> an invalid pointer. If we use numactl to bind a program to the node
    >>> after onlining the node and its memory, it will cause the kernel
    >>> panicked:
    >>
    >> Is there any chance we could get rid of the zone backpointer in lruvec
    >> again instead?
    >
    > It could be done, but it would make me sad :(
    >
    >> Adding new nodes is a rare event and so updating every
    >> single memcg in the system might be just borderline crazy.
    >
    > Not horribly crazy, but rather ugly, yes.
    >
    >> But can't
    >> we just go back to passing the zone along with the lruvec down
    >> vmscan.c paths? I agree it's ugly to pass both, given their
    >> relationship. But I don't think the backpointer is any cleaner but in
    >> addition less robust.
    >
    > It's like how we use vma->mm: we could change everywhere to pass mm with
    > vma, but it looks cleaner and cuts down on long arglists to have mm in vma.
    >>From past experience, one of the things I worried about was adding extra
    > args to the reclaim stack.
    >
    >>
    >> That being said, the crashing code in particular makes me wonder:
    >>
    >> static __always_inline void add_page_to_lru_list(struct page *page,
    >> struct lruvec *lruvec, enum lru_list lru)
    >> {
    >> int nr_pages = hpage_nr_pages(page);
    >> mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
    >> list_add(&page->lru, &lruvec->lists[lru]);
    >> __mod_zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru, nr_pages);
    >> }
    >>
    >> Why did we ever pass zone in here and then felt the need to replace it
    >> with lruvec->zone in fa9add6 "mm/memcg: apply add/del_page to lruvec"?
    >> A page does not roam between zones, its zone is a static property that
    >> can be retrieved with page_zone().
    >
    > Just as in vmscan.c, we have the lruvec to hand, and that's what we
    > mainly want to operate upon, but there is also some need for zone.
    >
    > (Both Konstantin and I were looking towards the day when we move the
    > lru_lock into the lruvec, removing more dependence on "zone". Pretty
    > much the only reason that hasn't happened yet, is that we have not found
    > time to make a performance case convincingly - but that's another topic.)
    >
    > Yes, page_zone(page) is a static property of the page, but it's not
    > necessarily cheap to evaluate: depends on how complex the memory model
    > and the spare page flags space, doesn't it? We both preferred to
    > derive zone from lruvec where convenient.
    >
    > How do you feel about this patch, and does it work for you guys?
    >
    > You'd be right if you guessed that I started out without the
    > mem_cgroup_zone_lruvec part of it, but oops in get_scan_count
    > told me that's needed too.
    >
    > Description to be filled in later: would it be needed for -stable,
    > or is onlining already broken in other ways that you're now fixing up?

    We will test your patch, please wait some time.

    >
    > Reported-by: Tang Chen <tangchen@cn.fujitsu.com>
    > Signed-off-by: Hugh Dickins <hughd@google.com>
    > ---
    >
    > include/linux/mmzone.h | 2 -
    > mm/memcontrol.c | 40 ++++++++++++++++++++++++++++++++-------
    > mm/mmzone.c | 6 -----
    > mm/page_alloc.c | 2 -
    > 4 files changed, 36 insertions(+), 14 deletions(-)
    >
    > --- 3.6-rc5/include/linux/mmzone.h 2012-08-03 08:31:26.892842267 -0700
    > +++ linux/include/linux/mmzone.h 2012-09-13 17:07:51.893772372 -0700
    > @@ -744,7 +744,7 @@ extern int init_currently_empty_zone(str
    > unsigned long size,
    > enum memmap_context context);
    >
    > -extern void lruvec_init(struct lruvec *lruvec, struct zone *zone);
    > +extern void lruvec_init(struct lruvec *lruvec);
    >
    > static inline struct zone *lruvec_zone(struct lruvec *lruvec)
    > {
    > --- 3.6-rc5/mm/memcontrol.c 2012-08-03 08:31:27.060842270 -0700
    > +++ linux/mm/memcontrol.c 2012-09-13 17:46:36.870804625 -0700
    > @@ -1061,12 +1061,25 @@ struct lruvec *mem_cgroup_zone_lruvec(st
    > struct mem_cgroup *memcg)
    > {
    > struct mem_cgroup_per_zone *mz;
    > + struct lruvec *lruvec;
    >
    > - if (mem_cgroup_disabled())
    > - return &zone->lruvec;
    > + if (mem_cgroup_disabled()) {
    > + lruvec = &zone->lruvec;
    > + goto out;
    > + }
    >
    > mz = mem_cgroup_zoneinfo(memcg, zone_to_nid(zone), zone_idx(zone));
    > - return &mz->lruvec;
    > + lruvec = &mz->lruvec;
    > +out:
    > + /*
    > + * Since a node can be onlined after the mem_cgroup was created,
    > + * we have to be prepared to initialize lruvec->zone here.
    > + */
    > + if (unlikely(lruvec->zone != zone)) {
    > + VM_BUG_ON(lruvec->zone);
    > + lruvec->zone = zone;
    > + }
    > + return lruvec;
    > }
    >
    > /*
    > @@ -1093,9 +1106,12 @@ struct lruvec *mem_cgroup_page_lruvec(st
    > struct mem_cgroup_per_zone *mz;
    > struct mem_cgroup *memcg;
    > struct page_cgroup *pc;
    > + struct lruvec *lruvec;
    >
    > - if (mem_cgroup_disabled())
    > - return &zone->lruvec;
    > + if (mem_cgroup_disabled()) {
    > + lruvec = &zone->lruvec;
    > + goto out;
    > + }
    >
    > pc = lookup_page_cgroup(page);
    > memcg = pc->mem_cgroup;
    > @@ -1113,7 +1129,17 @@ struct lruvec *mem_cgroup_page_lruvec(st
    > pc->mem_cgroup = memcg = root_mem_cgroup;
    >
    > mz = page_cgroup_zoneinfo(memcg, page);
    > - return &mz->lruvec;
    > + lruvec = &mz->lruvec;
    > +out:
    > + /*
    > + * Since a node can be onlined after the mem_cgroup was created,
    > + * we have to be prepared to initialize lruvec->zone here.
    > + */
    > + if (unlikely(lruvec->zone != zone)) {
    > + VM_BUG_ON(lruvec->zone);

    According your comment, lruver->zone != zone if a node is onlined. So
    it is not a bug, and VM_BUG_ON() should not be used here.

    Thanks
    Wen Congyang

    > + lruvec->zone = zone;
    > + }
    > + return lruvec;
    > }
    >
    > /**
    > @@ -4742,7 +4768,7 @@ static int alloc_mem_cgroup_per_zone_inf
    >
    > for (zone = 0; zone < MAX_NR_ZONES; zone++) {
    > mz = &pn->zoneinfo[zone];
    > - lruvec_init(&mz->lruvec, &NODE_DATA(node)->node_zones[zone]);
    > + lruvec_init(&mz->lruvec);
    > mz->usage_in_excess = 0;
    > mz->on_tree = false;
    > mz->memcg = memcg;
    > --- 3.6-rc5/mm/mmzone.c 2012-08-03 08:31:27.064842271 -0700
    > +++ linux/mm/mmzone.c 2012-09-13 17:06:28.921766001 -0700
    > @@ -87,7 +87,7 @@ int memmap_valid_within(unsigned long pf
    > }
    > #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
    >
    > -void lruvec_init(struct lruvec *lruvec, struct zone *zone)
    > +void lruvec_init(struct lruvec *lruvec)
    > {
    > enum lru_list lru;
    >
    > @@ -95,8 +95,4 @@ void lruvec_init(struct lruvec *lruvec,
    >
    > for_each_lru(lru)
    > INIT_LIST_HEAD(&lruvec->lists[lru]);
    > -
    > -#ifdef CONFIG_MEMCG
    > - lruvec->zone = zone;
    > -#endif
    > }
    > --- 3.6-rc5/mm/page_alloc.c 2012-08-22 14:25:39.508279046 -0700
    > +++ linux/mm/page_alloc.c 2012-09-13 17:06:08.265763526 -0700
    > @@ -4456,7 +4456,7 @@ static void __paginginit free_area_init_
    > zone->zone_pgdat = pgdat;
    >
    > zone_pcp_init(zone);
    > - lruvec_init(&zone->lruvec, zone);
    > + lruvec_init(&zone->lruvec);
    > if (!size)
    > continue;
    >
    >



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