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Message-ID: <AANLkTi=bo1H1+DxrgPjTRH7+kk9T6=BMO3mAC78=-1uG@mail.gmail.com>
Date: Tue, 1 Mar 2011 13:13:58 -0800
From: Greg Thelen <gthelen@...gle.com>
To: Minchan Kim <minchan.kim@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Wu Fengguang <fengguang.wu@...el.com>,
Chad Talbott <ctalbott@...gle.com>,
Justin TerAvest <teravest@...gle.com>,
Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v5 4/9] writeback: create dirty_info structure
On Sun, Feb 27, 2011 at 8:38 AM, Minchan Kim <minchan.kim@...il.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@...gle.com>
>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Reviewed-by: Minchan Kim <minchan.kim@...il.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
>
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