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Preserved-over-Kexec RAM To: Baoquan He Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, rppt@kernel.org, akpm@linux-foundation.org, ebiederm@xmission.com, keescook@chromium.org, graf@amazon.com, jason.zeng@intel.com, lei.l.li@intel.com, steven.sistare@oracle.com, fam.zheng@bytedance.com, mgalaxy@akamai.com, kexec@lists.infradead.org References: <1682554137-13938-1-git-send-email-anthony.yznaga@oracle.com> Content-Language: en-US From: Anthony Yznaga In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR04CA0005.namprd04.prod.outlook.com (2603:10b6:a03:1d0::15) To BYAPR10MB2438.namprd10.prod.outlook.com (2603:10b6:a02:aa::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB2438:EE_|IA1PR10MB6241:EE_ 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linux-kernel@vger.kernel.org On 5/31/23 7:15 PM, Baoquan He wrote: > On 04/26/23 at 05:08pm, Anthony Yznaga wrote: >> Sending out this RFC in part to guage community interest. >> This patchset implements preserved-over-kexec memory storage or PKRAM as a >> method for saving memory pages of the currently executing kernel so that >> they may be restored after kexec into a new kernel. The patches are adapted >> from an RFC patchset sent out in 2013 by Vladimir Davydov [1]. They >> introduce the PKRAM kernel API. >> >> One use case for PKRAM is preserving guest memory and/or auxillary >> supporting data (e.g. iommu data) across kexec to support reboot of the >> host with minimal disruption to the guest. PKRAM provides a flexible way >> for doing this without requiring that the amount of memory used by a fixed >> size created a priori. Another use case is for databases to preserve their >> block caches in shared memory across reboot. > If so, I have confusions, who can help clarify: > 1) Why kexec reboot was introduced, what do we expect kexec reboot to > do? > > 2) If we need keep these data and those data, can we not reboot? They > are definitely located there w/o any concern. > > 3) What if systems of AI, edge computing, HPC etc also want to carry > kinds of data from userspace or kernel, system status, registers > etc when kexec reboot is needed, while enligntened by this patch? Hi Baoquan, Avoiding a more significant disruption from having to halt or migrate VMs, failover services, etc. when a reboot is necessary to pick up security fixes is one motivation for exploring preserving memory across the reboot. Anthony > > Thanks > Baoquan >