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Message-ID: <20180422030130.GG14610@bombadil.infradead.org> Date: Sat, 21 Apr 2018 20:01:30 -0700 From: Matthew Wilcox <willy@...radead.org> To: Vlastimil Babka <vbabka@...e.cz> Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.com>, Huang Ying <ying.huang@...el.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Pavel Tatashin <pasha.tatashin@...cle.com>, Miles Chen <miles.chen@...iatek.com>, Mel Gorman <mgorman@...hsingularity.net>, Rik van Riel <riel@...hat.com>, James Hogan <jhogan@...nel.org>, "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>, open list <linux-kernel@...r.kernel.org> Subject: Re: [PATCH RFC 2/8] mm: introduce PG_offline On Sat, Apr 21, 2018 at 06:52:18PM +0200, Vlastimil Babka wrote: > On 04/13/2018 07:11 PM, Matthew Wilcox wrote: > > On Fri, Apr 13, 2018 at 03:16:26PM +0200, David Hildenbrand wrote: > >> online_pages()/offline_pages() theoretically allows us to work on > >> sub-section sizes. This is especially relevant in the context of > >> virtualization. It e.g. allows us to add/remove memory to Linux in a VM in > >> 4MB chunks. > >> > >> While the whole section is marked as online/offline, we have to know > >> the state of each page. E.g. to not read memory that is not online > >> during kexec() or to properly mark a section as offline as soon as all > >> contained pages are offline. > > > > Can you not use PG_reserved for this purpose? > > Sounds like your newly introduced "page types" could be useful here? I > don't suppose those offline pages would be using mapcount which is > aliased there? Oh, that's a good point! Yes, this is a perfect use for page_type. We have something like twenty bits available there. Now you've got me thinking that we can move PG_hwpoison and PG_reserved to be page_type flags too. That'll take us from 23 to 21 bits (on 32-bit, with PG_UNCACHED)
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