From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH RFC 2/6] mm: convert PG_balloon to PG_offline Date: Wed, 14 Nov 2018 23:49:15 +0100 Message-ID: References: <20181114211704.6381-1-david@redhat.com> <20181114211704.6381-3-david@redhat.com> <20181114222321.GB1784@bombadil.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181114222321.GB1784@bombadil.infradead.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, devel@linuxdriverproject.org, linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org, xen-devel@lists.xenproject.org, Jonathan Corbet , Alexey Dobriyan , Mike Rapoport , Andrew Morton , Christian Hansen , Vlastimil Babka , "Kirill A. Shutemov" , Stephen Rothwell , "Michael S. Tsirkin" , Michal Hocko , Pavel Tatashin , Alexander Duyck , Naoya Horiguchi , Miles Chen List-Id: linux-pm@vger.kernel.org On 14.11.18 23:23, Matthew Wilcox wrote: > On Wed, Nov 14, 2018 at 10:17:00PM +0100, David Hildenbrand wrote: >> Rename PG_balloon to PG_offline. This is an indicator that the page is >> logically offline, the content stale and that it should not be touched >> (e.g. a hypervisor would have to allocate backing storage in order for the >> guest to dump an unused page). We can then e.g. exclude such pages from >> dumps. >> >> In following patches, we will make use of this bit also in other balloon >> drivers. While at it, document PGTABLE. > > Thank you for documenting PGTABLE. I didn't realise I also had this > document to update when I added PGTABLE. Thank you for looking into this :) > >> +++ b/Documentation/admin-guide/mm/pagemap.rst >> @@ -78,6 +78,8 @@ number of times a page is mapped. >> 23. BALLOON >> 24. ZERO_PAGE >> 25. IDLE >> + 26. PGTABLE >> + 27. OFFLINE > > So the offline *user* bit is new ... even though the *kernel* bit > just renames the balloon bit. I'm not sure how I feel about this. > I'm going to think about it some more. Could you share your decision > process with us? BALLOON was/is documented as "23 - BALLOON balloon compaction page " and only includes all virtio-ballon pages after the non-lru migration feature has been implemented for ballooned pages. Since then, this flag does basically no longer stands for what it actually was supposed to do. To not break uapi I decided to not rename it but instead to add a new flag. > > I have no objection to renaming the balloon bit inside the kernel; I > think that's a wise idea. I'm just not sure whether we should rename > the user balloon bit rather than adding a new bit. > Can we rename without breaking uapi? -- Thanks, David / dhildenb