linux-kernel - Re: [PATCH 2/2] writeback: Adding pages_dirtied and pages_entered

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Date:	Thu, 5 Aug 2010 13:24:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michael Rubin <mrubin@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, jack@...e.cz, david@...morbit.com, hch@....de,
	axboe@...nel.dk
Subject: Re: [PATCH 2/2] writeback: Adding pages_dirtied and
 pages_entered_writeback

On Wed,  4 Aug 2010 17:43:24 -0700
Michael Rubin <mrubin@...gle.com> wrote:

> To help developers and applications gain visibility into writeback
> behaviour adding four read only sysctl files into /proc/sys/vm.
> These files allow user apps to understand writeback behaviour over time
> and learn how it is impacting their performance.
> 
>    # cat /proc/sys/vm/pages_dirtied
>    3747
>    # cat /proc/sys/vm/pages_entered_writeback
>    3618
> 
> Documentation/vm.txt has been updated.
> 
> In order to track the "cleaned" and "dirtied" counts we added two
> vm_stat_items.  Per memory node stats have been added also. So we can
> see per node granularity:
> 
>    # cat /sys/devices/system/node/node20/writebackstat
>    Node 20 pages_writeback: 0 times
>    Node 20 pages_dirtied: 0 times
> 
> ...
>
> @@ -1091,6 +1115,7 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
>  {
>  	if (mapping_cap_account_dirty(mapping)) {
>  		__inc_zone_page_state(page, NR_FILE_DIRTY);
> +		__inc_zone_page_state(page, NR_FILE_PAGES_DIRTIED);
>  		__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
>  		task_dirty_inc(current);
>  		task_io_account_write(PAGE_CACHE_SIZE);

I hope the utility of this change is worth the overhead :(

> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -740,6 +740,8 @@ static const char * const vmstat_text[] = {
>  	"numa_local",
>  	"numa_other",
>  #endif
> +	"nr_pages_entered_writeback",
> +	"nr_file_pages_dirtied",
>  

Wait.  These counters appear in /proc/vmstat.  So why create standalone
/proc/sys/vm files as well?

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