linux-kernel - Re: [PATCH] VM: kswapd should not do blocking memory allocations

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Message-ID: <20100820054016.GA11847@localhost>
Date:	Fri, 20 Aug 2010 13:40:16 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org
Subject: Re: [PATCH] VM: kswapd should not do blocking memory allocations

On Wed, Aug 18, 2010 at 03:04:01PM -0400, Trond Myklebust wrote:
> From: Trond Myklebust <Trond.Myklebust@...app.com>
> 
> Allowing kswapd to do GFP_KERNEL memory allocations (or any blocking memory
> allocations) is wrong and can cause deadlocks in try_to_release_page(), as
> the filesystem believes it is safe to allocate new memory and block,
> whereas kswapd is there specifically to clear a low-memory situation...
> 
> Set the gfp_mask to GFP_IOFS instead.

It would be more descriptive to say "remove the __GFP_WAIT bit".

The change looks reasonable _in itself_, since we always prefer to
avoid unnecessary waits for kswapd. So

Acked-by: Wu Fengguang <fengguang.wu@...el.com>

> Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
> ---
> 
>  mm/vmscan.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ec5ddcc..716dd16 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2095,7 +2095,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
>  	unsigned long total_scanned;
>  	struct reclaim_state *reclaim_state = current->reclaim_state;
>  	struct scan_control sc = {
> -		.gfp_mask = GFP_KERNEL,
> +		.gfp_mask = GFP_IOFS,
>  		.may_unmap = 1,
>  		.may_swap = 1,
>  		/*
> 
> --
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