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

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Date:	Thu, 25 Apr 2013 18:29:58 +0400
From:	"Maxim V. Patlasov" <mpatlasov@...allels.com>
To:	"miklos@...redi.hu" <miklos@...redi.hu>
CC:	<dev@...allels.com>, <xemul@...allels.com>,
	"fuse-devel@...ts.sourceforge.net" <fuse-devel@...ts.sourceforge.net>,
	<linux-kernel@...r.kernel.org>, <jbottomley@...allels.com>,
	<viro@...iv.linux.org.uk>, <linux-fsdevel@...r.kernel.org>,
	<devel@...nvz.org>, <akpm@...ux-foundation.org>,
	<fengguang.wu@...el.com>
Subject: Re: [fuse-devel] [PATCH 14/14] mm: Account for WRITEBACK_TEMP in
 balance_dirty_pages

Hi Miklos,

04/01/2013 02:42 PM, Maxim V. Patlasov пишет:
> 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 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 0713bfb..c47bcd4 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1235,7 +1235,8 @@ 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);
>   
>   		global_dirty_limits(&background_thresh, &dirty_thresh);

Please drop this patch. As we discussed in LSF/MM, the fix above is 
correct, but it's not enough: we also need to ensure disregard of 
NR_WRITEBACK_TEMP when balance_dirty_pages() is called from fuse daemon. 
I'll send a separate patch-set soon.

Thanks,
Maxim
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