linux-kernel - Re: [RFC PATCH 3/4] xfs: map KM_MAYFAIL to __GFP_RETRY

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Message-ID: <20170307170519.GE5281@birch.djwong.org>
Date:   Tue, 7 Mar 2017 09:05:19 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 3/4] xfs: map KM_MAYFAIL to __GFP_RETRY_MAYFAIL

On Tue, Mar 07, 2017 at 04:48:42PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> KM_MAYFAIL didn't have any suitable GFP_FOO counterpart until recently
> so it relied on the default page allocator behavior for the given set
> of flags. This means that small allocations actually never failed.
> 
> Now that we have __GFP_RETRY_MAYFAIL flag which works independently on the
> allocation request size we can map KM_MAYFAIL to it. The allocator will
> try as hard as it can to fulfill the request but fails eventually if
> the progress cannot be made.
> 
> Cc: Darrick J. Wong <darrick.wong@...cle.com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  fs/xfs/kmem.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
> index ae08cfd9552a..ac80a4855c83 100644
> --- a/fs/xfs/kmem.h
> +++ b/fs/xfs/kmem.h
> @@ -54,6 +54,16 @@ kmem_flags_convert(xfs_km_flags_t flags)
>  			lflags &= ~__GFP_FS;
>  	}
>  
> +	/*
> +	 * Default page/slab allocator behavior is to retry for ever
> +	 * for small allocations. We can override this behavior by using
> +	 * __GFP_RETRY_MAYFAIL which will tell the allocator to retry as long
> +	 * as it is feasible but rather fail than retry for ever for all

s/for ever/forever/

> +	 * request sizes.
> +	 */
> +	if (flags & KM_MAYFAIL)
> +		lflags |= __GFP_RETRY_MAYFAIL;

But otherwise seems ok from a quick grep -B5 MAYFAIL through the XFS code.

(Has this been tested anywhere?)

--D

> +
>  	if (flags & KM_ZERO)
>  		lflags |= __GFP_ZERO;
>  
> -- 
> 2.11.0
>