memcg: add per cgroup writeback pages accounting

Add memcg routines to count writeback pages, later dirty pages will also
be accounted.

After Kame's commit 89c06bd52fb9 ("memcg: use new logic for page stat
accounting"), we can use 'struct page' flag to test page state instead
of per page_cgroup flag.  But memcg has a feature to move a page from a
cgroup to another one and may have race between "move" and "page stat
accounting".  So in order to avoid the race we have designed a new lock:

         mem_cgroup_begin_update_page_stat()
         modify page information        -->(a)
         mem_cgroup_update_page_stat()  -->(b)
         mem_cgroup_end_update_page_stat()

It requires both (a) and (b)(writeback pages accounting) to be pretected
in mem_cgroup_{begin/end}_update_page_stat().  It's full no-op for
!CONFIG_MEMCG, almost no-op if memcg is disabled (but compiled in), rcu
read lock in the most cases (no task is moving), and spin_lock_irqsave
on top in the slow path.

There're two writeback interfaces to modify: test_{clear/set}_page_writeback().
And the lock order is:
	--> memcg->move_lock
	  --> mapping->tree_lock

Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Greg Thelen <gthelen@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f952a07..60e9587 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -42,6 +42,7 @@ enum mem_cgroup_stat_index {
        MEM_CGROUP_STAT_RSS,            /* # of pages charged as anon rss */
        MEM_CGROUP_STAT_RSS_HUGE,       /* # of pages charged as anon huge */
        MEM_CGROUP_STAT_FILE_MAPPED,    /* # of pages charged as file rss */
+       MEM_CGROUP_STAT_WRITEBACK,      /* # of pages under writeback */
        MEM_CGROUP_STAT_SWAP,           /* # of pages, swapped out */
        MEM_CGROUP_STAT_NSTATS,
 };

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0093bc3..d5ff3ce 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -89,6 +89,7 @@ static const char * const mem_cgroup_stat_names[] = {
        "rss",
        "rss_huge",
        "mapped_file",
+       "writeback",
        "swap",
 };
 
@@ -3654,6 +3655,20 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
+static inline
+void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
+                                       struct mem_cgroup *to,
+                                       unsigned int nr_pages,
+                                       enum mem_cgroup_stat_index idx)
+{
+       /* Update stat data for mem_cgroup */
+       preempt_disable();
+       WARN_ON_ONCE(from->stat->count[idx] < nr_pages);
+       __this_cpu_add(from->stat->count[idx], -nr_pages);
+       __this_cpu_add(to->stat->count[idx], nr_pages);
+       preempt_enable();
+}
+
 /**
  * mem_cgroup_move_account - move account of the page
  * @page: the page
@@ -3699,13 +3714,14 @@ static int mem_cgroup_move_account(struct page *page,
 
        move_lock_mem_cgroup(from, &flags);
 
-       if (!anon && page_mapped(page)) {
-               /* Update mapped_file data for mem_cgroup */
-               preempt_disable();
-               __this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
-               __this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
-               preempt_enable();
-       }
+       if (!anon && page_mapped(page))
+               mem_cgroup_move_account_page_stat(from, to, nr_pages,
+                       MEM_CGROUP_STAT_FILE_MAPPED);
+
+       if (PageWriteback(page))
+               mem_cgroup_move_account_page_stat(from, to, nr_pages,
+                       MEM_CGROUP_STAT_WRITEBACK);
+
        mem_cgroup_charge_statistics(from, page, anon, -nr_pages);
 
        /* caller should have done css_get */

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6c7b018..f5236f8 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2143,11 +2143,17 @@ EXPORT_SYMBOL(account_page_dirtied);
 
 /*
  * Helper function for set_page_writeback family.
+ *
+ * The caller must hold mem_cgroup_begin/end_update_page_stat() lock
+ * while calling this function.
+ * See test_set_page_writeback for example.
+ *
  * NOTE: Unlike account_page_dirtied this does not rely on being atomic
  * wrt interrupts.
  */
 void account_page_writeback(struct page *page)
 {
+       mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
        inc_zone_page_state(page, NR_WRITEBACK);
 }
 EXPORT_SYMBOL(account_page_writeback);
@@ -2364,7 +2370,10 @@ int test_clear_page_writeback(struct page *page)
 {
        struct address_space *mapping = page_mapping(page);
        int ret;
+       bool locked;
+       unsigned long memcg_flags;
 
+       mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
        if (mapping) {
                struct backing_dev_info *bdi = mapping->backing_dev_info;
                unsigned long flags;
@@ -2385,9 +2394,11 @@ int test_clear_page_writeback(struct page *page)
                ret = TestClearPageWriteback(page);
        }
        if (ret) {
+               mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
                dec_zone_page_state(page, NR_WRITEBACK);
                inc_zone_page_state(page, NR_WRITTEN);
        }
+       mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
        return ret;
 }
 
@@ -2395,7 +2406,10 @@ int test_set_page_writeback(struct page *page)
 {
        struct address_space *mapping = page_mapping(page);
        int ret;
+       bool locked;
+       unsigned long memcg_flags;
 
+       mem_cgroup_begin_update_page_stat(page, &locked, &memcg_flags);
        if (mapping) {
                struct backing_dev_info *bdi = mapping->backing_dev_info;
                unsigned long flags;
@@ -2422,6 +2436,7 @@ int test_set_page_writeback(struct page *page)
        }
        if (!ret)
                account_page_writeback(page);
+       mem_cgroup_end_update_page_stat(page, &locked, &memcg_flags);
        return ret;
 
 }