On 19/12/2019 08:52, Durrant, Paul wrote: >> -----Original Message----- >> From: Xen-devel <xen-devel-boun...@lists.xenproject.org> On Behalf Of >> Andrew Cooper >> Sent: 18 December 2019 19:45 >> To: Durrant, Paul <pdurr...@amazon.com>; xen-devel@lists.xenproject.org >> Cc: Wei Liu <w...@xen.org>; Jan Beulich <jbeul...@suse.com>; Roger Pau Monné >> <roger....@citrix.com> >> Subject: Re: [Xen-devel] [PATCH] x86/save: reserve HVM save record numbers >> that have been consumed... >> >> On 18/12/2019 16:09, Paul Durrant wrote: >>> ...for patches not (yet) upstream. >>> >>> This patch is simply reserving save record number space to avoid the >>> risk of clashes between existent downstream changes made by Amazon and >>> future upstream changes which may be incompatible. >>> >>> Signed-off-by: Paul Durrant <pdurr...@amazon.com> >> Is this "you've already used some of these", or you plan to? > Already used in code that has been deployed, although I have left some > headroom because I know there is code in development which is using new ones. > > Where records can be upstreamed in a way that is compatible with downstream > use, we will keep the existing number. If incompatible changes are necessary > to get the code upstream then we will have to use a new number and maintain > downstream compatibility patches.
Every bump to this number is more wasted memory in Xen. It is not fair or reasonable to include extra headroom in a "oh dear we screwed up - will the community be kind enough to help us work around our ABI problems" scenario. For now, I'd just leave it as a comment, and strictly only covering the ones you have used. There is no need to actually bump the structure sizes in xen for now - simply that the ones you have currently used don't get allocated for something different in the future. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
