From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Ingo Korb <ingo@akana.de>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, mel@csn.ul.ie,
cl@linux-foundation.org, yinghai@kernel.org,
andi.kleen@intel.com, linux-kernel@vger.kernel.org
Subject: Re: PROBLEM: __offline_isolated_pages may offline too many pages
Date: Wed, 15 Dec 2010 09:21:34 +0900 [thread overview]
Message-ID: <20101215092134.e2c8849f.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <4D0786D3.7070007@akana.de>
On Tue, 14 Dec 2010 16:01:39 +0100
Ingo Korb <ingo@akana.de> wrote:
> Hi!
>
> [1.] One line summary of the problem:
> __offline_isolated_pages may isolate too many pages
>
> [2.] Full description of the problem/report:
> While experimenting with remove_memory/online_pages, removing as few
> pages as possible (pageblock_nr_pages, 512 on my box) I noticed that the
> number of pages marked "reserved" increased even though both functions
> did not indicate an error. Following the code it was clear that
> __offline_isolated_pages marked twice as many pages as it should:
>
It's designed for offline memory section > MAX_ORDER. pageblock_nr_pages
is tend to be smaller than that.
Do you see the problem with _exsisting_ user interface of memory hotplug ?
I think we have no control other than memory section.
> === start paste (from dmesg) ===
> Offlined Pages 512
> remove from free list c00 1024 e00
> === end paste ===
>
> The issue seems to be that __offline_isolated_pages blindly uses
> page_order() to determine how many pages it should mark as reserved in
> the current loop iteration, without checking if this would exceed the
> limit set by end_pfn.
>
It's because designed to work under memory section, it's aligned to MAX_ORDER.
Its blindness works correctly.
> I'm not sure what the correct way to fix this would be - is memory
> isolation supposed to touch the order of a page if it crosses the end
> (or beginning!) of the range of pages to be isolated?
>
Nothing to be fixed. If you _need_ another functionality, please add a new
feature. But, in theory, memory offline doesn't work in the range smaller
than MAX_ORDER because of buddy allocator.
Thanks,
-Kame
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next prev parent reply other threads:[~2010-12-15 0:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-14 15:01 Ingo Korb
2010-12-15 0:21 ` KAMEZAWA Hiroyuki [this message]
2010-12-15 9:25 ` Ingo Korb
2010-12-16 0:06 ` KAMEZAWA Hiroyuki
2010-12-16 10:26 ` Mel Gorman
2010-12-16 23:57 ` [PATCH] memory hotplug: fix alignment check (Was " KAMEZAWA Hiroyuki
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