linux-kernel - Re: [PATCH 4/8] mm/writeback: Throttle based on page writeback instead of congestion

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Date:   Thu, 14 Oct 2021 17:34:42 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux-MM <linux-mm@...ck.org>
Cc:     NeilBrown <neilb@...e.de>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] mm/writeback: Throttle based on page writeback
 instead of congestion

On 10/8/21 15:53, Mel Gorman wrote:
> do_writepages throttles on congestion if the writepages() fails due to a
> lack of memory but congestion_wait() is partially broken as the congestion
> state is not updated for all BDIs.
> 
> This patch stalls waiting for a number of pages to complete writeback
> that located on the local node. The main weakness is that there is no
> correlation between the location of the inode's pages and locality but
> that is still better than congestion_wait.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/page-writeback.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 4812a17b288c..f34f54fcd5b4 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2366,8 +2366,15 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
>  			ret = generic_writepages(mapping, wbc);
>  		if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
>  			break;
> -		cond_resched();
> -		congestion_wait(BLK_RW_ASYNC, HZ/50);
> +
> +		/*
> +		 * Lacking an allocation context or the locality or writeback
> +		 * state of any of the inode's pages, throttle based on
> +		 * writeback activity on the local node. It's as good a
> +		 * guess as any.
> +		 */
> +		reclaim_throttle(NODE_DATA(numa_node_id()),
> +			VMSCAN_THROTTLE_WRITEBACK, HZ/50);
>  	}
>  	/*
>  	 * Usually few pages are written by now from those we've just submitted
>