Hi,
just a minor comment/suggestion. The patch would be much more easier to
review if you split it up into two parts. Preparatory with page->memcg
parameter change and the locking change you are proposing.
On Sat 26-01-13 19:12:36, Sha Zhengju wrote:
[...]
> So in order to make the lock simpler and clearer and also avoid the 'nesting'
> problem, a choice may be:
> (CPU-A does "page stat accounting" and CPU-B does "move")
>
> CPU-A CPU-B
>
> move_lock_mem_cgroup()
> memcg = pc->mem_cgroup
> TestSetPageDirty(page)
> move_unlock_mem_cgroup()
> move_lock_mem_cgroup()
> if (PageDirty) {
> old_memcg->nr_dirty --;
> new_memcg->nr_dirty ++;
> }
> pc->mem_cgroup = new_memcg
> move_unlock_mem_cgroup()
>
> memcg->nr_dirty ++
>
> For CPU-A, we save pc->mem_cgroup in a temporary variable just before
> TestSetPageDirty inside move_lock and then update stats if the page is set
> PG_dirty successfully.
Hmm, the description is a bit confising. You are talking about
TestSetPageDirty but dirty accounting is not directly handled in the
patch. It took me a bit to figure that it's actually set_page_dirty
called from page_remove_rmap which matters here. So it is more a
dependency between MEMCG_NR_FILE_MAPPED and your future (currently
non-existent) MEMCG_NR_FILE_DIRTY accounting that you are preparing.
set_page_dirty now can take mem_cgroup_{begin,end}_update_page_stat.
> But CPU-B may do "moving" in advance that
> "old_memcg->nr_dirty --" will make old_memcg->nr_dirty incorrect but
> soon CPU-A will do "memcg->nr_dirty ++" finally that amend the stats.
The counter is per-cpu so we are safe wrt. atomic increments and we can
probably tolerate off-by 1 temporal errors (mem_cgroup_read_stat would
need val = min(val, 0);).
I am not sure I like this very much though. It adds an additional memcg
reference counting into page_add_file which is a hot path already.
I think the accounting side should be as lightweight as possible and the
additional price should be payed by mover.
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 14 +++++------
> mm/memcontrol.c | 8 ++-----
> mm/rmap.c | 55 +++++++++++++++++++++++++++++++++-----------
> 3 files changed, 51 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0108a56..12de53b 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -164,20 +164,20 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
> rcu_read_unlock();
> }
>
> -void mem_cgroup_update_page_stat(struct page *page,
> +void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx,
> int val);
>
> -static inline void mem_cgroup_inc_page_stat(struct page *page,
> +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx)
> {
> - mem_cgroup_update_page_stat(page, idx, 1);
> + mem_cgroup_update_page_stat(memcg, idx, 1);
> }
>
> -static inline void mem_cgroup_dec_page_stat(struct page *page,
> +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx)
> {
> - mem_cgroup_update_page_stat(page, idx, -1);
> + mem_cgroup_update_page_stat(memcg, idx, -1);
> }
>
> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> @@ -354,12 +354,12 @@ static inline void mem_cgroup_end_update_page_stat(struct page *page,
> {
> }
>
> -static inline void mem_cgroup_inc_page_stat(struct page *page,
> +static inline void mem_cgroup_inc_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx)
> {
> }
>
> -static inline void mem_cgroup_dec_page_stat(struct page *page,
> +static inline void mem_cgroup_dec_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx)
> {
> }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3817460..1b13e43 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2259,18 +2259,14 @@ void __mem_cgroup_end_update_page_stat(struct page *page, unsigned long *flags)
> move_unlock_mem_cgroup(pc->mem_cgroup, flags);
> }
>
> -void mem_cgroup_update_page_stat(struct page *page,
> +void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
> enum mem_cgroup_page_stat_item idx, int val)
> {
> - struct mem_cgroup *memcg;
> - struct page_cgroup *pc = lookup_page_cgroup(page);
> - unsigned long uninitialized_var(flags);
>
> if (mem_cgroup_disabled())
> return;
>
> - memcg = pc->mem_cgroup;
> - if (unlikely(!memcg || !PageCgroupUsed(pc)))
> + if (unlikely(!memcg))
> return;
>
> switch (idx) {
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 59b0dca..0d74c48 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1112,13 +1112,25 @@ void page_add_file_rmap(struct page *page)
> {
> bool locked;
> unsigned long flags;
> + bool ret;
> + struct mem_cgroup *memcg = NULL;
> + struct cgroup_subsys_state *css = NULL;
>
> mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> - if (atomic_inc_and_test(&page->_mapcount)) {
> + memcg = try_get_mem_cgroup_from_page(page);
> + ret = atomic_inc_and_test(&page->_mapcount);
> + mem_cgroup_end_update_page_stat(page, &locked, &flags);
> +
> + if (ret) {
> __inc_zone_page_state(page, NR_FILE_MAPPED);
> - mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
> + if (memcg)
> + mem_cgroup_inc_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
> + }
> +
> + if (memcg) {
> + css = mem_cgroup_css(memcg);
> + css_put(css);
> }
> - mem_cgroup_end_update_page_stat(page, &locked, &flags);
> }
>
> /**
> @@ -1133,18 +1145,32 @@ void page_remove_rmap(struct page *page)
> bool anon = PageAnon(page);
> bool locked;
> unsigned long flags;
> + struct mem_cgroup *memcg = NULL;
> + struct cgroup_subsys_state *css = NULL;
> + bool ret;
>
> /*
> * The anon case has no mem_cgroup page_stat to update; but may
> * uncharge_page() below, where the lock ordering can deadlock if
> * we hold the lock against page_stat move: so avoid it on anon.
> */
> - if (!anon)
> + if (!anon) {
> mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> + memcg = try_get_mem_cgroup_from_page(page);
> + if (memcg)
> + css = mem_cgroup_css(memcg);
> + }
> +
> + ret = atomic_add_negative(-1, &page->_mapcount);
> + if (!anon)
> + mem_cgroup_end_update_page_stat(page, &locked, &flags);
>
> /* page still mapped by someone else? */
> - if (!atomic_add_negative(-1, &page->_mapcount))
> - goto out;
> + if (!ret) {
> + if (!anon && memcg)
> + css_put(css);
> + return;
> + }
>
> /*
> * Now that the last pte has gone, s390 must transfer dirty
> @@ -1173,8 +1199,12 @@ void page_remove_rmap(struct page *page)
> * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
> * and not charged by memcg for now.
> */
> - if (unlikely(PageHuge(page)))
> - goto out;
> + if (unlikely(PageHuge(page))) {
> + if (!anon && memcg)
> + css_put(css);
> + return;
> + }
> +
> if (anon) {
> mem_cgroup_uncharge_page(page);
> if (!PageTransHuge(page))
> @@ -1184,8 +1214,10 @@ void page_remove_rmap(struct page *page)
> NR_ANON_TRANSPARENT_HUGEPAGES);
> } else {
> __dec_zone_page_state(page, NR_FILE_MAPPED);
> - mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
> - mem_cgroup_end_update_page_stat(page, &locked, &flags);
> + if (memcg) {
> + mem_cgroup_dec_page_stat(memcg, MEMCG_NR_FILE_MAPPED);
> + css_put(css);
> + }
> }
> if (unlikely(PageMlocked(page)))
> clear_page_mlock(page);
> @@ -1199,9 +1231,6 @@ void page_remove_rmap(struct page *page)
> * faster for those pages still in swapcache.
> */
> return;
> -out:
> - if (!anon)
> - mem_cgroup_end_update_page_stat(page, &locked, &flags);
> }
>
> /*
> --
> 1.7.9.5
>
> --
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--
Michal Hocko
SUSE Labs
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