linux-kernel - Re: [PATCH 5/8] mm/page_alloc: Remove the throttling logic from the page allocator

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Date:   Thu, 14 Oct 2021 17:36:22 +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 5/8] mm/page_alloc: Remove the throttling logic from the
 page allocator

On 10/8/21 15:53, Mel Gorman wrote:
> The page allocator stalls based on the number of pages that are
> waiting for writeback to start but this should now be redundant.
> shrink_inactive_list() will wake flusher threads if the LRU tail are
> unqueued dirty pages so the flusher should be active. If it fails to make
> progress due to pages under writeback not being completed quickly then
> it should stall on VMSCAN_THROTTLE_WRITEBACK.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

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

> ---
>  mm/page_alloc.c | 21 +--------------------
>  1 file changed, 1 insertion(+), 20 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 78e538067651..8fa0109ff417 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4795,30 +4795,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
>  		trace_reclaim_retry_zone(z, order, reclaimable,
>  				available, min_wmark, *no_progress_loops, wmark);
>  		if (wmark) {
> -			/*
> -			 * If we didn't make any progress and have a lot of
> -			 * dirty + writeback pages then we should wait for
> -			 * an IO to complete to slow down the reclaim and
> -			 * prevent from pre mature OOM
> -			 */
> -			if (!did_some_progress) {
> -				unsigned long write_pending;
> -
> -				write_pending = zone_page_state_snapshot(zone,
> -							NR_ZONE_WRITE_PENDING);
> -
> -				if (2 * write_pending > reclaimable) {
> -					congestion_wait(BLK_RW_ASYNC, HZ/10);
> -					return true;
> -				}
> -			}
> -
>  			ret = true;
> -			goto out;
> +			break;
>  		}
>  	}
>  
> -out:
>  	/*
>  	 * Memory allocation/reclaim might be called from a WQ context and the
>  	 * current implementation of the WQ concurrency control doesn't
>