linux-kernel - Re: [PATCH 3/3] mm: fix return value in __alloc_contig_migrate

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Date:	Mon, 16 Jul 2012 19:40:56 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Marek Szyprowski <m.szyprowski@...sung.com>,
	Minchan Kim <minchan@...nel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 3/3] mm: fix return value in __alloc_contig_migrate_range()

Joonsoo Kim <js1304@...il.com> writes:

> migrate_pages() would return positive value in some failure case,
> so 'ret > 0 ? 0 : ret' may be wrong.
> This fix it and remove one dead statement.
>
> Signed-off-by: Joonsoo Kim <js1304@...il.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Christoph Lameter <cl@...ux.com>

Have you actually encountered this problem?  If migrate_pages() fails
with a positive value, the code that you are removing kicks in and
-EBUSY is assigned to ret (now that I look at it, I think that in the
current code the "return ret > 0 ? 0 : ret;" statement could be reduced
to "return ret;").  Your code seems to be cleaner, but the commit
message does not look accurate to me.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4403009..02d4519 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5673,7 +5673,6 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
>  			}
>  			tries = 0;
>  		} else if (++tries == 5) {
> -			ret = ret < 0 ? ret : -EBUSY;
>  			break;
>  		}
>  
> @@ -5683,7 +5682,7 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
>  	}
>  
>  	putback_lru_pages(&cc.migratepages);
> -	return ret > 0 ? 0 : ret;
> +	return ret <= 0 ? ret : -EBUSY;
>  }
>  
>  /*

-- 
Best regards,                                          _     _
 .o. | Liege of Serenly Enlightened Majesty of       o' \,=./ `o
 ..o | Computer Science,  Michal "mina86" Nazarewicz    (o o)
 ooo +-<mina86-mina86.com>-<jid:mina86-jabber.org>--ooO--(_)--Ooo--

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