linux-kernel - RE: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose is_mem_section

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Message-ID: <PS1P15301MB034764C1FFA3D2711DAED14C92360@PS1P15301MB0347.APCP153.PROD.OUTLOOK.COM>
Date:   Fri, 17 Jan 2020 16:35:03 +0000
From:   Tianyu Lan <Tianyu.Lan@...rosoft.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     David Hildenbrand <david@...hat.com>,
        "lantianyu1986@...il.com" <lantianyu1986@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        vkuznets <vkuznets@...hat.com>,
        "eric.devolder@...cle.com" <eric.devolder@...cle.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "osalvador@...e.de" <osalvador@...e.de>,
        Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>
Subject: RE: [EXTERNAL] Re: [RFC PATCH V2 2/10] mm: expose
 is_mem_section_removable() symbol

> From: Michal Hocko <mhocko@...nel.org>
> Sent: Tuesday, January 14, 2020 5:51 PM
> To: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> Cc: David Hildenbrand <david@...hat.com>; lantianyu1986@...il.com; KY
> Srinivasan <kys@...rosoft.com>; Haiyang Zhang <haiyangz@...rosoft.com>;
> Stephen Hemminger <sthemmin@...rosoft.com>; sashal@...nel.org;
> akpm@...ux-foundation.org; Michael Kelley <mikelley@...rosoft.com>; linux-
> hyperv@...r.kernel.org; linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> vkuznets <vkuznets@...hat.com>; eric.devolder@...cle.com; vbabka@...e.cz;
> osalvador@...e.de; Pasha Tatashin <Pavel.Tatashin@...rosoft.com>;
> rppt@...ux.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.