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Thu, 26 May 2022 13:16:23 +0000 Received: from CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::bd49:f0ab:b476:860c]) by CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::bd49:f0ab:b476:860c%8]) with mapi id 15.20.5293.013; Thu, 26 May 2022 13:16:23 +0000 Message-ID: Date: Thu, 26 May 2022 08:16:16 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.1 Subject: Re: [PATCH v8 0/7] crash: Kernel handling of CPU and memory hot un/plug Content-Language: en-US To: Sourabh Jain , linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com References: <20220505184603.1548-1-eric.devolder@oracle.com> <311b0834-c675-fd15-8184-82b122f4a9cc@linux.ibm.com> From: Eric DeVolder In-Reply-To: <311b0834-c675-fd15-8184-82b122f4a9cc@linux.ibm.com> Content-Type: text/plain; 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In previous posts I have >> outlined the significant performance problems related to offloading >> this activity to userspace. >> >> This patchset introduces a generic crash hot un/plug handler that >> registers with the CPU and memory notifiers. Upon CPU or memory >> changes, this generic handler is invoked and performs important >> housekeeping, for example obtaining the appropriate lock, and then >> invokes an architecture specific handler to do the appropriate >> updates. >> >> In the case of x86_64, the arch specific handler generates a new >> elfcorehdr, and overwrites the old one in memory. No involvement >> with userspace needed. >> >> To realize the benefits/test this patchset, one must make a couple >> of minor changes to userspace: >> >>   - Disable the udev rule for updating kdump on hot un/plug changes. >>     Add the following as the first two lines to the udev rule file >>     /usr/lib/udev/rules.d/98-kexec.rules: > > If we can have a sysfs attribute to advertise this feature then userspace > utilities (kexec tool/udev rules) can take action accordingly. In short, it will > help us maintain backward compatibility. > > kexec tool can use the new sysfs attribute and allocate additional buffer space > for elfcorehdr accordingly. Similarly, the checksum-related changes can come > under this check. > > Udev rule can use this sysfs file to decide kdump service reload is required or not. Great idea. I've been working on the corresponding udev and kexec-tools changes and your input/idea here is quite timely. I have boolean "crash_hotplug" as a core_param(), so it will show up as: # cat /sys/module/kernel/parameters/crash_hotplug N This will provide userspace the indication it needs. > > Thanks, > Sourabh Jain >