linux-kernel - Re: [PATCH 3/4] mm: vmscan: Evaluate the watermarks against the correct classzone

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Date:	Mon, 27 Jun 2011 15:53:04 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pádraig Brady <P@...igbrady.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Colin King <colin.king@...onical.com>,
	Andrew Lutomirski <luto@....edu>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] mm: vmscan: Evaluate the watermarks against the
 correct classzone

On Fri, Jun 24, 2011 at 11:44 PM, Mel Gorman <mgorman@...e.de> wrote:
> When deciding if kswapd is sleeping prematurely, the classzone is
> taken into account but this is different to what balance_pgdat() and
> the allocator are doing. Specifically, the DMA zone will be checked
> based on the classzone used when waking kswapd which could be for a
> GFP_KERNEL or GFP_HIGHMEM request. The lowmem reserve limit kicks in,
> the watermark is not met and kswapd thinks its sleeping prematurely
> keeping kswapd awake in error.


I thought it was intentional when you submitted a patch firstly.
"Kswapd makes sure zones include enough free pages(ie, include reserve
limit of above zones).
But you seem to see DMA zone can't meet above requirement forever in
some situation so that kswapd doesn't sleep.
Right?

>
> Reported-and-tested-by: Pádraig Brady <P@...igBrady.com>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  mm/vmscan.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9cebed1..a76b6cc2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2341,7 +2341,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>                }
>
>                if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
> -                                                       classzone_idx, 0))
> +                                                       i, 0))

Isn't it  better to use 0 instead of i?

-- 
Kind regards,
Minchan Kim
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