RE: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose is_mem_section_removable() symbol

From: Tianyu Lan <Tianyu.Lan@microsoft.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
	"lantianyu1986@gmail.com" <lantianyu1986@gmail.com>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"sashal@kernel.org" <sashal@kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	Michael Kelley <mikelley@microsoft.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	vkuznets <vkuznets@redhat.com>,
	"eric.devolder@oracle.com" <eric.devolder@oracle.com>,
	"vbabka@suse.cz" <vbabka@suse.cz>,
	"osalvador@suse.de" <osalvador@suse.de>,
	Pasha Tatashin <Pavel.Tatashin@microsoft.com>,
	"rppt@linux.ibm.com" <rppt@linux.ibm.com>
Subject: RE: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose is_mem_section_removable() symbol
Date: Fri, 17 Jan 2020 16:35:03 +0000	[thread overview]
Message-ID: <PS1P15301MB034764C1FFA3D2711DAED14C92360@PS1P15301MB0347.APCP153.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20200114095057.GK19428@dhcp22.suse.cz>

> From: Michal Hocko <mhocko@kernel.org>
> Sent: Tuesday, January 14, 2020 5:51 PM
> To: Tianyu Lan <Tianyu.Lan@microsoft.com>
> Cc: David Hildenbrand <david@redhat.com>; lantianyu1986@gmail.com; KY
> Srinivasan <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>;
> Stephen Hemminger <sthemmin@microsoft.com>; sashal@kernel.org;
> akpm@linux-foundation.org; Michael Kelley <mikelley@microsoft.com>; linux-
> hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> vkuznets <vkuznets@redhat.com>; eric.devolder@oracle.com; vbabka@suse.cz;
> osalvador@suse.de; Pasha Tatashin <Pavel.Tatashin@microsoft.com>;
> rppt@linux.ibm.com
> Subject: Re: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose
> is_mem_section_removable() symbol
> 
> On Mon 13-01-20 14:49:38, Tianyu Lan wrote:
> > Hi David & Michal:
> > 	Thanks for your review. Some memory blocks are not suitable for hot-
> plug.
> > If not check memory block's removable, offline_pages() will report
> > some failure error e.g, "failed due to memory holes" and  "failure to
> > isolate range". I think the check maybe added into
> > offline_and_remove_memory()? This may help to not create/expose a new
> interface to do such check in module.
> 
> Why is a log message a problem in the first place. The operation has failed
> afterall. Does the driver try to offline an arbitrary memory?

Yes.

> Could you describe your usecase in more details please?

Hyper-V sends hot-remove request message which just contains requested
page number but not provide detail range. So Hyper-V driver needs to search
suitable memory block in system memory to return back to host if there is no
memory hot-add before. So I used the is_mem_section_removable() do such check.