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    SubjectRe: [PATCH 2/2] memcg: add per cgroup dirty pages accounting
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    On Fri, Jun 15, 2012 at 11:32 PM, Greg Thelen <gthelen@google.com> wrote:
    > On Fri, Jun 15 2012, Sha Zhengju wrote:
    >
    >> This patch adds memcg routines to count dirty pages. I notice that
    >> the list has talked about per-cgroup dirty page limiting
    >> (http://lwn.net/Articles/455341/) before, but it did not get merged.
    >
    > Good timing, I was just about to make another effort to get some of
    > these patches upstream.  Like you, I was going to start with some basic
    > counters.
    >
    > Your approach is similar to what I have in mind.  While it is good to
    > use the existing PageDirty flag, rather than introducing a new
    > page_cgroup flag, there are locking complications (see below) to handle
    > races between moving pages between memcg and the pages being {un}marked
    > dirty.
    >
    >> I've no idea how is this going now, but maybe we can add per cgroup
    >> dirty pages accounting first. This allows the memory controller to
    >> maintain an accurate view of the amount of its memory that is dirty
    >> and can provide some infomation while group's direct reclaim is working.
    >>
    >> After commit 89c06bd5 (memcg: use new logic for page stat accounting),
    >> we do not need per page_cgroup flag anymore and can directly use
    >> struct page flag.
    >>
    >>
    >> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
    >> ---
    >>  include/linux/memcontrol.h |    1 +
    >>  mm/filemap.c               |    1 +
    >>  mm/memcontrol.c            |   32 +++++++++++++++++++++++++-------
    >>  mm/page-writeback.c        |    2 ++
    >>  mm/truncate.c              |    1 +
    >>  5 files changed, 30 insertions(+), 7 deletions(-)
    >>
    >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
    >> index a337c2e..8154ade 100644
    >> --- a/include/linux/memcontrol.h
    >> +++ b/include/linux/memcontrol.h
    >> @@ -39,6 +39,7 @@ enum mem_cgroup_stat_index {
    >>       MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
    >>       MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
    >>       MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
    >> +     MEM_CGROUP_STAT_FILE_DIRTY,  /* # of dirty pages in page cache */
    >>       MEM_CGROUP_STAT_NSTATS,
    >>  };
    >>
    >> diff --git a/mm/filemap.c b/mm/filemap.c
    >> index 79c4b2b..5b5c121 100644
    >> --- a/mm/filemap.c
    >> +++ b/mm/filemap.c
    >> @@ -141,6 +141,7 @@ void __delete_from_page_cache(struct page *page)
    >>        * having removed the page entirely.
    >>        */
    >>       if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
    >> +             mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
    >
    > You need to use mem_cgroup_{begin,end}_update_page_stat around critical
    > sections that:
    > 1) check PageDirty
    > 2) update MEM_CGROUP_STAT_FILE_DIRTY counter
    >
    > This protects against the page from being moved between memcg while
    > accounting.  Same comment applies to all of your new calls to
    > mem_cgroup_{dec,inc}_page_stat.  For usage pattern, see
    > page_add_file_rmap.


    It seems I should call mem_cgroup_{begin,end}_update_page_stat to prevent race
    while modifying struct page info.
    Thanks for patiently explaining!


    >
    >>               dec_zone_page_state(page, NR_FILE_DIRTY);
    >>               dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
    >>       }
    >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    >> index 9102b8c..d200ad1 100644
    >> --- a/mm/memcontrol.c
    >> +++ b/mm/memcontrol.c
    >> @@ -2548,6 +2548,18 @@ 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,
    >> +                                     enum mem_cgroup_stat_index idx)
    >> +{
    >> +     /* Update stat data for mem_cgroup */
    >> +     preempt_disable();
    >> +     __this_cpu_dec(from->stat->count[idx]);
    >> +     __this_cpu_inc(to->stat->count[idx]);
    >> +     preempt_enable();
    >> +}
    >> +
    >>  /**
    >>   * mem_cgroup_move_account - move account of the page
    >>   * @page: the page
    >> @@ -2597,13 +2609,14 @@ 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,
    >> +                                     MEM_CGROUP_STAT_FILE_MAPPED);
    >> +
    >> +     if (PageDirty(page))
    >> +             mem_cgroup_move_account_page_stat(from, to,
    >> +                                     MEM_CGROUP_STAT_FILE_DIRTY);
    >> +
    >>       mem_cgroup_charge_statistics(from, anon, -nr_pages);
    >>       if (uncharge)
    >>               /* This is not "cancel", but cancel_charge does all we need. */
    >> @@ -4023,6 +4036,7 @@ enum {
    >>       MCS_SWAP,
    >>       MCS_PGFAULT,
    >>       MCS_PGMAJFAULT,
    >> +     MCS_FILE_DIRTY,
    >>       MCS_INACTIVE_ANON,
    >>       MCS_ACTIVE_ANON,
    >>       MCS_INACTIVE_FILE,
    >> @@ -4047,6 +4061,7 @@ struct {
    >>       {"swap", "total_swap"},
    >>       {"pgfault", "total_pgfault"},
    >>       {"pgmajfault", "total_pgmajfault"},
    >> +     {"dirty", "total_dirty"},
    >
    > Please add something to Documentation/cgroups/memory.txt describing this
    > new user visible data.  See my previous patch
    > http://thread.gmane.org/gmane.linux.kernel.mm/67114 for example text.
    >


    Got it. I'll add it in next version.

    Thanks,
    Sha


    >>       {"inactive_anon", "total_inactive_anon"},
    >>       {"active_anon", "total_active_anon"},
    >>       {"inactive_file", "total_inactive_file"},
    >> @@ -4080,6 +4095,9 @@ mem_cgroup_get_local_stat(struct mem_cgroup *memcg, struct mcs_total_stat *s)
    >>       val = mem_cgroup_read_events(memcg, MEM_CGROUP_EVENTS_PGMAJFAULT);
    >>       s->stat[MCS_PGMAJFAULT] += val;
    >>
    >> +     val = mem_cgroup_read_stat(memcg, MEM_CGROUP_STAT_FILE_DIRTY);
    >> +     s->stat[MCS_FILE_DIRTY] += val * PAGE_SIZE;
    >> +
    >>       /* per zone stat */
    >>       val = mem_cgroup_nr_lru_pages(memcg, BIT(LRU_INACTIVE_ANON));
    >>       s->stat[MCS_INACTIVE_ANON] += val * PAGE_SIZE;
    >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    >> index 26adea8..b17c692 100644
    >> --- a/mm/page-writeback.c
    >> +++ b/mm/page-writeback.c
    >> @@ -1936,6 +1936,7 @@ int __set_page_dirty_no_writeback(struct page *page)
    >>  void account_page_dirtied(struct page *page, struct address_space *mapping)
    >>  {
    >>       if (mapping_cap_account_dirty(mapping)) {
    >> +             mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
    >>               __inc_zone_page_state(page, NR_FILE_DIRTY);
    >>               __inc_zone_page_state(page, NR_DIRTIED);
    >>               __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
    >> @@ -2155,6 +2156,7 @@ int clear_page_dirty_for_io(struct page *page)
    >>                * for more comments.
    >>                */
    >>               if (TestClearPageDirty(page)) {
    >> +                     mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
    >>                       dec_zone_page_state(page, NR_FILE_DIRTY);
    >>                       dec_bdi_stat(mapping->backing_dev_info,
    >>                                       BDI_RECLAIMABLE);
    >> diff --git a/mm/truncate.c b/mm/truncate.c
    >> index 61a183b..fe8363e 100644
    >> --- a/mm/truncate.c
    >> +++ b/mm/truncate.c
    >> @@ -76,6 +76,7 @@ void cancel_dirty_page(struct page *page, unsigned int account_size)
    >>       if (TestClearPageDirty(page)) {
    >>               struct address_space *mapping = page->mapping;
    >>               if (mapping && mapping_cap_account_dirty(mapping)) {
    >> +                     mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_DIRTY);
    >>                       dec_zone_page_state(page, NR_FILE_DIRTY);
    >>                       dec_bdi_stat(mapping->backing_dev_info,
    >>                                       BDI_RECLAIMABLE);
    --
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