linux-kernel - Re: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining memory blocks

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Message-ID: <51F13E51.7040808@sr71.net>
Date:	Thu, 25 Jul 2013 08:03:45 -0700
From:	Dave Hansen <dave@...1.net>
To:	KY Srinivasan <kys@...rosoft.com>
CC:	Michal Hocko <mhocko@...e.cz>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"kamezawa.hiroyuki@...il.com" <kamezawa.hiroyuki@...il.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"yinghan@...gle.com" <yinghan@...gle.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"kay@...y.org" <kay@...y.org>
Subject: Re: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining
 memory blocks

On 07/25/2013 04:14 AM, KY Srinivasan wrote:
> As promised, I have sent out the patches for (a) an implementation of an in-kernel API
> for onlining  and a consumer for this API. While I don't know the exact reason why the
> user mode code is delayed (under some low memory conditions), what is the harm in having
> a mechanism to online memory that has been hot added without involving user space code.

KY, your potential problem, not being able to online more memory because
of a shortage of memory, is a serious one.

However, this potential issue exists in long-standing code, and
potentially affects all users of memory hotplug.  The problem has not
been described in sufficient detail for the rest of the developers to
tell if you are facing a new problem, or whether *any* proposed solution
will help the problem you face.

Your propsed solution changes the semantics of existing user/kernel
interfaces, duplicates existing functionality, and adds code complexity
to the kernel.
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