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

[Tianyu Lan]

> From: Michal Hocko <mhocko@xxxxxxxxxx>
> Sent: Tuesday, January 14, 2020 5:51 PM
> To: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>; lantianyu1986@xxxxxxxxx; KY
> Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>;
> Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>; sashal@xxxxxxxxxx;
> akpm@xxxxxxxxxxxxxxxxxxxx; Michael Kelley <mikelley@xxxxxxxxxxxxx>; linux-
> hyperv@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx;
> vkuznets <vkuznets@xxxxxxxxxx>; eric.devolder@xxxxxxxxxx; vbabka@xxxxxxx;
> osalvador@xxxxxxx; Pasha Tatashin <Pavel.Tatashin@xxxxxxxxxxxxx>;
> rppt@xxxxxxxxxxxxx
> 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.