From: Mel Gorman <mgorman@suse.de>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Michal Hocko <mhocko@suse.cz>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>
Subject: Re: mm: page_alloc: avoid marking zones full prematurely after zone_reclaim()
Date: Tue, 2 Apr 2013 11:37:13 +0100 [thread overview]
Message-ID: <20130402103713.GD32241@suse.de> (raw)
In-Reply-To: <20130401111324.GY18466@mwanda>
On Mon, Apr 01, 2013 at 02:13:24PM +0300, Dan Carpenter wrote:
> I still don't understand the code in gfp_to_alloc_flags().
>
> int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
>
> ORing with zero is odd.
>
Thanks Dan for the report and thanks Michal for fixing it. I was offline
for last week which lead to my tardy response.
The odditiy is that ALLOC_WMARK_MIN is not treated as a flag but as an
offset within the zone->wmark so it starts as 0. It could have been
written as
int alloc_flags = ALLOC_CPUSET;
but then it would be easy to forget that in this path we are using the
MIN watermark.
The "flag" is used as an offset because it eliminated a number of
branches in the page allocator and was a micro-optimisation at the time.
--
Mel Gorman
SUSE Labs
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prev parent reply other threads:[~2013-04-02 10:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-27 6:01 mm: page_alloc: avoid marking zones full prematurely after zone_reclaim() Dan Carpenter
2013-03-27 16:55 ` Michal Hocko
2013-03-27 17:13 ` Michal Hocko
2013-04-01 11:13 ` Dan Carpenter
2013-04-02 9:55 ` Michal Hocko
2013-04-02 10:37 ` Mel Gorman [this message]
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