From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Oliver O'Halloran <oohall@gmail.com>,
linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC PATCH] mm/init: fix zone boundary creation
Date: Mon, 30 May 2016 10:15:04 +0100 [thread overview]
Message-ID: <20160530091504.GN2527@techsingularity.net> (raw)
In-Reply-To: <20160526142142.b16f7f3f18204faf0823ac65@linux-foundation.org>
On Thu, May 26, 2016 at 02:21:42PM -0700, Andrew Morton wrote:
> On Thu, 5 May 2016 17:57:13 +1000 "Oliver O'Halloran" <oohall@gmail.com> wrote:
>
> > As a part of memory initialisation the architecture passes an array to
> > free_area_init_nodes() which specifies the max PFN of each memory zone.
> > This array is not necessarily monotonic (due to unused zones) so this
> > array is parsed to build monotonic lists of the min and max PFN for
> > each zone. ZONE_MOVABLE is special cased here as its limits are managed by
> > the mm subsystem rather than the architecture. Unfortunately, this special
> > casing is broken when ZONE_MOVABLE is the not the last zone in the zone
> > list. The core of the issue is:
> >
> > if (i == ZONE_MOVABLE)
> > continue;
> > arch_zone_lowest_possible_pfn[i] =
> > arch_zone_highest_possible_pfn[i-1];
> >
> > As ZONE_MOVABLE is skipped the lowest_possible_pfn of the next zone
> > will be set to zero. This patch fixes this bug by adding explicitly
> > tracking where the next zone should start rather than relying on the
> > contents arch_zone_highest_possible_pfn[].
>
> hm, this is all ten year old Mel code.
>
ZONE_MOVABLE at the time always existed at the end of a node during
initialisation time. It was allowed because the memory was always "stolen"
from the end of the node where it could have the same limitations as
ZONE_HIGHMEM if necessary. It was also safe to assume that zones never
overlapped as zones were about addressing limitations. If ZONE_CMA or
ZONE_DEVICE can overlap with other zones during initialisation time then
there may be a few gremlins hiding in there. Unfortunately I have not
done an audit searching for problems with overlapping zones.
--
Mel Gorman
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-05-30 9:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-05 7:57 [RFC PATCH] mm/init: fix zone boundary creation Oliver O'Halloran
2016-05-26 21:21 ` Andrew Morton
2016-05-27 8:03 ` oliver
2016-05-30 9:15 ` Mel Gorman [this message]
2016-05-30 13:18 ` oliver
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160530091504.GN2527@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=akpm@linux-foundation.org \
--cc=linux-mm@kvack.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=oohall@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).