Re: [PATCH v5 4/9] writeback: create dirty_info structure

[Greg Thelen <gthelen@google.com>]

On Sun, Feb 27, 2011 at 8:38 AM, Minchan Kim <minchan.kim@gmail.com> wrote:
> On Fri, Feb 25, 2011 at 01:35:55PM -0800, Greg Thelen wrote:
>> Bundle dirty limits and dirty memory usage metrics into a dirty_info
>> structure to simplify interfaces of routines that need all.
>>
>> Signed-off-by: Greg Thelen <gthelen@google.com>
>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
>
>> ---
>> Changelog since v4:
>> - Within new dirty_info structure, replaced nr_reclaimable with nr_file_dirty
>>   and nr_unstable_nfs to give callers finer grain dirty usage information.
>> - Added new dirty_info_reclaimable() function.
>> - Made more use of dirty_info structure in throttle_vm_writeout().
>>
>> Changelog since v3:
>> - This is a new patch in v4.
>>
>>  fs/fs-writeback.c         |    7 ++---
>>  include/linux/writeback.h |   15 ++++++++++++-
>>  mm/backing-dev.c          |   18 +++++++++------
>>  mm/page-writeback.c       |   50 ++++++++++++++++++++++----------------------
>>  mm/vmstat.c               |    6 +++-
>>  5 files changed, 57 insertions(+), 39 deletions(-)
>>
>> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> index 59c6e49..d75e4da 100644
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -595,12 +595,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
>>
>>  static inline bool over_bground_thresh(void)
>>  {
>> -     unsigned long background_thresh, dirty_thresh;
>> +     struct dirty_info info;
>>
>> -     global_dirty_limits(&background_thresh, &dirty_thresh);
>> +     global_dirty_info(&info);
>>
>> -     return (global_page_state(NR_FILE_DIRTY) +
>> -             global_page_state(NR_UNSTABLE_NFS) > background_thresh);
>> +     return dirty_info_reclaimable(&info) > info.background_thresh;
>>  }
>
> Get unnecessary nr_writeback.
>
>>
>>  /*
>> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
>> index 0ead399..a06fb38 100644
>> --- a/include/linux/writeback.h
>> +++ b/include/linux/writeback.h
>> @@ -84,6 +84,19 @@ static inline void inode_sync_wait(struct inode *inode)
>>  /*
>>   * mm/page-writeback.c
>>   */
>> +struct dirty_info {
>> +     unsigned long dirty_thresh;
>> +     unsigned long background_thresh;
>> +     unsigned long nr_file_dirty;
>> +     unsigned long nr_writeback;
>> +     unsigned long nr_unstable_nfs;
>> +};
>> +
>> +static inline unsigned long dirty_info_reclaimable(struct dirty_info *info)
>> +{
>> +     return info->nr_file_dirty + info->nr_unstable_nfs;
>> +}
>> +
>>  #ifdef CONFIG_BLOCK
>>  void laptop_io_completion(struct backing_dev_info *info);
>>  void laptop_sync_completion(void);
>> @@ -124,7 +137,7 @@ struct ctl_table;
>>  int dirty_writeback_centisecs_handler(struct ctl_table *, int,
>>                                     void __user *, size_t *, loff_t *);
>>
>> -void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
>> +void global_dirty_info(struct dirty_info *info);
>>  unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
>>                              unsigned long dirty);
>>
>> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
>> index 027100d..17a06ab 100644
>> --- a/mm/backing-dev.c
>> +++ b/mm/backing-dev.c
>> @@ -66,8 +66,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
>>  {
>>       struct backing_dev_info *bdi = m->private;
>>       struct bdi_writeback *wb = &bdi->wb;
>> -     unsigned long background_thresh;
>> -     unsigned long dirty_thresh;
>> +     struct dirty_info dirty_info;
>>       unsigned long bdi_thresh;
>>       unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
>>       struct inode *inode;
>> @@ -82,8 +81,8 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
>>               nr_more_io++;
>>       spin_unlock(&inode_lock);
>>
>> -     global_dirty_limits(&background_thresh, &dirty_thresh);
>> -     bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
>> +     global_dirty_info(&dirty_info);
>> +     bdi_thresh = bdi_dirty_limit(bdi, dirty_info.dirty_thresh);
>>
>>  #define K(x) ((x) << (PAGE_SHIFT - 10))
>>       seq_printf(m,
>> @@ -99,9 +98,14 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
>>                  "state:            %8lx\n",
>>                  (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
>>                  (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
>> -                K(bdi_thresh), K(dirty_thresh),
>> -                K(background_thresh), nr_dirty, nr_io, nr_more_io,
>> -                !list_empty(&bdi->bdi_list), bdi->state);
>> +                K(bdi_thresh),
>> +                K(dirty_info.dirty_thresh),
>> +                K(dirty_info.background_thresh),
>
> Get unnecessary nr_file_dirty, nr_writeback, nr_unstable_nfs.
>
>> +                nr_dirty,
>> +                nr_io,
>> +                nr_more_io,
>> +                !list_empty(&bdi->bdi_list),
>> +                bdi->state);
>>  #undef K
>>
>>       return 0;
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index 4408e54..00424b9 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -398,7 +398,7 @@ unsigned long determine_dirtyable_memory(void)
>>  }
>>
>>  /*
>> - * global_dirty_limits - background-writeback and dirty-throttling thresholds
>> + * global_dirty_info - return dirty thresholds and usage metrics
>>   *
>>   * Calculate the dirty thresholds based on sysctl parameters
>>   * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
>> @@ -406,7 +406,7 @@ unsigned long determine_dirtyable_memory(void)
>>   * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
>>   * real-time tasks.
>>   */
>> -void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>> +void global_dirty_info(struct dirty_info *info)
>>  {
>>       unsigned long background;
>>       unsigned long dirty;
>> @@ -426,6 +426,10 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>>       else
>>               background = (dirty_background_ratio * available_memory) / 100;
>>
>> +     info->nr_file_dirty = global_page_state(NR_FILE_DIRTY);
>> +     info->nr_writeback = global_page_state(NR_WRITEBACK);
>> +     info->nr_unstable_nfs = global_page_state(NR_UNSTABLE_NFS);
>> +
>>       if (background >= dirty)
>>               background = dirty / 2;
>>       tsk = current;
>> @@ -433,8 +437,8 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>>               background += background / 4;
>>               dirty += dirty / 4;
>>       }
>> -     *pbackground = background;
>> -     *pdirty = dirty;
>> +     info->background_thresh = background;
>> +     info->dirty_thresh = dirty;
>>  }
>>
>>  /*
>> @@ -478,12 +482,9 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
>>  static void balance_dirty_pages(struct address_space *mapping,
>>                               unsigned long write_chunk)
>>  {
>> -     unsigned long nr_reclaimable;
>> +     struct dirty_info sys_info;
>>       long bdi_nr_reclaimable;
>> -     unsigned long nr_writeback;
>>       long bdi_nr_writeback;
>> -     unsigned long background_thresh;
>> -     unsigned long dirty_thresh;
>>       unsigned long bdi_thresh;
>>       unsigned long pages_written = 0;
>>       unsigned long pause = 1;
>> @@ -498,22 +499,19 @@ static void balance_dirty_pages(struct address_space *mapping,
>>                       .range_cyclic   = 1,
>>               };
>>
>> -             nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
>> -                                     global_page_state(NR_UNSTABLE_NFS);
>> -             nr_writeback = global_page_state(NR_WRITEBACK);
>> -
>> -             global_dirty_limits(&background_thresh, &dirty_thresh);
>> +             global_dirty_info(&sys_info);
>>
>>               /*
>>                * Throttle it only when the background writeback cannot
>>                * catch-up. This avoids (excessively) small writeouts
>>                * when the bdi limits are ramping up.
>>                */
>> -             if (nr_reclaimable + nr_writeback <=
>> -                             (background_thresh + dirty_thresh) / 2)
>> +             if (dirty_info_reclaimable(&sys_info) + sys_info.nr_writeback <=
>> +                             (sys_info.background_thresh +
>> +                              sys_info.dirty_thresh) / 2)
>>                       break;
>>
>> -             bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
>> +             bdi_thresh = bdi_dirty_limit(bdi, sys_info.dirty_thresh);
>>               bdi_thresh = task_dirty_limit(current, bdi_thresh);
>>
>>               /*
>> @@ -542,7 +540,8 @@ static void balance_dirty_pages(struct address_space *mapping,
>>                */
>>               dirty_exceeded =
>>                       (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
>> -                     || (nr_reclaimable + nr_writeback > dirty_thresh);
>> +                     || (dirty_info_reclaimable(&sys_info) +
>> +                          sys_info.nr_writeback > sys_info.dirty_thresh);
>>
>>               if (!dirty_exceeded)
>>                       break;
>> @@ -595,7 +594,8 @@ static void balance_dirty_pages(struct address_space *mapping,
>>        * background_thresh, to keep the amount of dirty memory low.
>>        */
>>       if ((laptop_mode && pages_written) ||
>> -         (!laptop_mode && (nr_reclaimable > background_thresh)))
>> +         (!laptop_mode && (dirty_info_reclaimable(&sys_info) >
>> +                           sys_info.background_thresh)))
>>               bdi_start_background_writeback(bdi);
>>  }
>>
>> @@ -655,21 +655,21 @@ EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
>>
>>  void throttle_vm_writeout(gfp_t gfp_mask)
>>  {
>> -     unsigned long background_thresh;
>> -     unsigned long dirty_thresh;
>> +     struct dirty_info sys_info;
>>
>>          for ( ; ; ) {
>> -             global_dirty_limits(&background_thresh, &dirty_thresh);
>> +             global_dirty_info(&sys_info);
>
> Get unnecessary nr_file_dirty.
>
>>
>>                  /*
>>                   * Boost the allowable dirty threshold a bit for page
>>                   * allocators so they don't get DoS'ed by heavy writers
>>                   */
>> -                dirty_thresh += dirty_thresh / 10;      /* wheeee... */
>> +             sys_info.dirty_thresh +=
>> +                     sys_info.dirty_thresh / 10;      /* wheeee... */
>>
>> -                if (global_page_state(NR_UNSTABLE_NFS) +
>> -                     global_page_state(NR_WRITEBACK) <= dirty_thresh)
>> -                             break;
>> +             if (sys_info.nr_unstable_nfs +
>> +                 sys_info.nr_writeback <= sys_info.dirty_thresh)
>> +                     break;
>>                  congestion_wait(BLK_RW_ASYNC, HZ/10);
>>
>>               /*
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 0c3b504..ec95924 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -1044,6 +1044,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
>>  {
>>       unsigned long *v;
>>       int i, stat_items_size;
>> +     struct dirty_info dirty_info;
>>
>>       if (*pos >= ARRAY_SIZE(vmstat_text))
>>               return NULL;
>> @@ -1062,8 +1063,9 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
>>               v[i] = global_page_state(i);
>>       v += NR_VM_ZONE_STAT_ITEMS;
>>
>> -     global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD,
>> -                         v + NR_DIRTY_THRESHOLD);
>> +     global_dirty_info(&dirty_info);
>> +     v[NR_DIRTY_BG_THRESHOLD] = dirty_info.background_thresh;
>> +     v[NR_DIRTY_THRESHOLD] = dirty_info.dirty_thresh;
>>       v += NR_VM_WRITEBACK_STAT_ITEMS;
>
> Get unnecessary nr_file_dirty, nr_writeback, nr_unstable_nfs.
>
> The code itself doesn't have a problem. but although it makes code simple,
> sometime it get unnecessary information in that context. The global_page_state never
> cheap operation and we have been tried to reduce overhead in page-writeback.
> (16c4042f, e50e3720).
>
> Fortunately this patch doesn't increase balance_dirty_pages's overhead and
> things affected by this patch are not fast-path.
> So I think it doesn't have a problem.

I am doing a small restructure to address this feedback.  The plan is
to only use the new dirty_info structure for memcg limits and usage.
The global limits and usage variables and logic will not be changed.

> --
> Kind regards,
> Minchan Kim
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>