linux-kernel - Re: [PATCH 14/14] mm: Account for WRITEBACK_TEMP in balance_dirty

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Date:	Thu, 22 Nov 2012 21:27:30 +0800
From:	Jaegeuk Hanse <jaegeuk.hanse@...il.com>
To:	Maxim Patlasov <mpatlasov@...allels.com>
CC:	miklos@...redi.hu, dev@...allels.com, xemul@...allels.com,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	jbottomley@...allels.com, linux-mm@...ck.org,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 14/14] mm: Account for WRITEBACK_TEMP in balance_dirty_pages

On 11/21/2012 08:01 PM, Maxim Patlasov wrote:
> Added linux-mm@ to cc:. The patch can stand on it's own.
>
>> Make balance_dirty_pages start the throttling when the WRITEBACK_TEMP
>> counter is high enough. This prevents us from having too many dirty
>> pages on fuse, thus giving the userspace part of it a chance to write
>> stuff properly.
>>
>> Note, that the existing balance logic is per-bdi, i.e. if the fuse
>> user task gets stuck in the function this means, that it either
>> writes to the mountpoint it serves (but it can deadlock even without
>> the writeback) or it is writing to some _other_ dirty bdi and in the
>> latter case someone else will free the memory for it.
> Signed-off-by: Maxim V. Patlasov <MPatlasov@...allels.com>
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
> ---
>   mm/page-writeback.c |    3 ++-
>   1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 830893b..499a606 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1220,7 +1220,8 @@ static void balance_dirty_pages(struct address_space *mapping,
>   		 */
>   		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
>   					global_page_state(NR_UNSTABLE_NFS);
> -		nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
> +		nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK) +
> +			global_page_state(NR_WRITEBACK_TEMP);
>   

Could you explain NR_WRITEBACK_TEMP is used for accounting what? And 
when it will increase?

>   		global_dirty_limits(&background_thresh, &dirty_thresh);
>   
>
> --
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