Re: [PATCH v6 4/9] memcg: add kernel calls for memcg dirty page stats

[Greg Thelen <gthelen@google.com>]

On Mon, Mar 14, 2011 at 8:10 AM, Minchan Kim <minchan.kim@gmail.com> wrote:
> On Fri, Mar 11, 2011 at 10:43:26AM -0800, Greg Thelen wrote:
>> Add calls into memcg dirty page accounting.  Notify memcg when pages
>> transition between clean, file dirty, writeback, and unstable nfs.
>> This allows the memory controller to maintain an accurate view of
>> the amount of its memory that is dirty.
>>
>> Signed-off-by: Greg Thelen <gthelen@google.com>
>> Signed-off-by: Andrea Righi <arighi@develer.com>
>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
>> ---
>> Changelog since v5:
>> - moved accounting site in test_clear_page_writeback() and
>>   test_set_page_writeback().
>>
>>  fs/nfs/write.c      |    4 ++++
>>  mm/filemap.c        |    1 +
>>  mm/page-writeback.c |   10 ++++++++--
>>  mm/truncate.c       |    1 +
>>  4 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
>> index 42b92d7..7863777 100644
>> --- a/fs/nfs/write.c
>> +++ b/fs/nfs/write.c
>> @@ -451,6 +451,7 @@ nfs_mark_request_commit(struct nfs_page *req)
>>                       NFS_PAGE_TAG_COMMIT);
>>       nfsi->ncommit++;
>>       spin_unlock(&inode->i_lock);
>> +     mem_cgroup_inc_page_stat(req->wb_page, MEMCG_NR_FILE_UNSTABLE_NFS);
>>       inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
>>       inc_bdi_stat(req->wb_page->mapping->backing_dev_info, BDI_RECLAIMABLE);
>>       __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
>> @@ -462,6 +463,7 @@ nfs_clear_request_commit(struct nfs_page *req)
>>       struct page *page = req->wb_page;
>>
>>       if (test_and_clear_bit(PG_CLEAN, &(req)->wb_flags)) {
>> +             mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_UNSTABLE_NFS);
>>               dec_zone_page_state(page, NR_UNSTABLE_NFS);
>>               dec_bdi_stat(page->mapping->backing_dev_info, BDI_RECLAIMABLE);
>>               return 1;
>> @@ -1319,6 +1321,8 @@ nfs_commit_list(struct inode *inode, struct list_head *head, int how)
>>               req = nfs_list_entry(head->next);
>>               nfs_list_remove_request(req);
>>               nfs_mark_request_commit(req);
>> +             mem_cgroup_dec_page_stat(req->wb_page,
>> +                                      MEMCG_NR_FILE_UNSTABLE_NFS);
>>               dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
>>               dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
>>                               BDI_RECLAIMABLE);
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index a6cfecf..7e751fe 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -143,6 +143,7 @@ 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, MEMCG_NR_FILE_DIRTY);
>>               dec_zone_page_state(page, NR_FILE_DIRTY);
>>               dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
>>       }
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index 632b464..d8005b0 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -1118,6 +1118,7 @@ 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, MEMCG_NR_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);
>> @@ -1317,6 +1318,7 @@ int clear_page_dirty_for_io(struct page *page)
>>                * for more comments.
>>                */
>>               if (TestClearPageDirty(page)) {
>> +                     mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_DIRTY);
>>                       dec_zone_page_state(page, NR_FILE_DIRTY);
>>                       dec_bdi_stat(mapping->backing_dev_info,
>>                                       BDI_RECLAIMABLE);
>> @@ -1352,8 +1354,10 @@ int test_clear_page_writeback(struct page *page)
>>       } else {
>>               ret = TestClearPageWriteback(page);
>>       }
>> -     if (ret)
>> +     if (ret) {
>> +             mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_WRITEBACK);
>>               dec_zone_page_state(page, NR_WRITEBACK);
>> +     }
>>       return ret;
>>  }
>>
>> @@ -1386,8 +1390,10 @@ int test_set_page_writeback(struct page *page)
>>       } else {
>>               ret = TestSetPageWriteback(page);
>>       }
>> -     if (!ret)
>> +     if (!ret) {
>> +             mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_WRITEBACK);
>>               account_page_writeback(page);
>> +     }
>>       return ret;
>>
>>  }
>
> At least in mainline, NR_WRITEBACK handling codes are following as.
>
> 1) increase
>
>  * account_page_writeback
>
> 2) decrease
>
>  * test_clear_page_writeback
>  * __nilfs_end_page_io
>
> I think account_page_writeback name is good to add your account function into that.
> The problem is decreasement. Normall we can handle decreasement in test_clear_page_writeback.
> But I am not sure it's okay in __nilfs_end_page_io.
> I think if __nilfs_end_page_io is right, __nilfs_end_page_io should call
> mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_WRITEBACK).
>
> What do you think about it?
>
>
>
> --
> Kind regards,
> Minchan Kim
>

I would like to not have any special cases that avoid certain memory.
So I think your suggestion is good.
However, nilfs memcg dirty page accounting was skipped in a previous
memcg dirty limit effort due to complexity.  See 'clone_page'
reference in:
  http://lkml.indiana.edu/hypermail/linux/kernel/1003.0/02997.html

I admit that I don't follow all of the nilfs code path, but it looks
like some of the nilfs pages are allocated but not charged to memcg.
There is code in mem_cgroup_update_page_stat() to gracefully handle
pages not associated with a memcg.  So perhaps nilfs clone pages dirty
[un]charge could be attempted.  I have not succeeded in testing in
exercising these code paths in nilfs.

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