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Tue, 16 Sep 2025 13:11:17 -0700 (PDT) Message-ID: Date: Tue, 16 Sep 2025 23:11:15 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Invitation] Linux MM Alignment Session on kmemdump on Wednesday To: Shakeel Butt Cc: Matthew Wilcox , Amit Shah , Andrew Morton , Aneesh Kumar , Christoph Lameter , Dave Hansen , David Hildenbrand , Davidlohr Bueso , Hugh Dickins , Johannes Weiner , John Hubbard , Kirill Shutemov , Mel Gorman , Michal Hocko , Mike Rapoport , Peter Xu , Raghavendra K T , "Rao, Bharata Bhasker" , Rik van Riel , Roman Gushchin , Shivank Garg , Sterling Alexander , Suren Baghdasaryan , Tejun Heo , Vlastimil Babka , Yang Shi , Zi Yan , linux-mm@kvack.org, rdunlap@infradead.org, David Rientjes References: <426751f4-428b-ed01-509b-d13e719a2006@google.com> <50b566d6-aeda-48cc-bd67-362cb29b214a@linaro.org> Content-Language: en-US From: Eugen Hristev In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: AC313140008 X-Stat-Signature: o49k3uekswg134jqo448mfzb3bahx569 X-Rspam-User: X-HE-Tag: 1758053479-842827 X-HE-Meta: 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 ids9/OGM 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/16/25 18:36, Shakeel Butt wrote: > On Tue, Sep 16, 2025 at 03:14:48PM +0300, Eugen Hristev wrote: >> >> >> On 9/16/25 15:07, Matthew Wilcox wrote: >>> On Tue, Sep 16, 2025 at 11:49:35AM +0300, Eugen Hristev wrote: >>>> On 9/15/25 21:53, Matthew Wilcox wrote: >>>>> On Mon, Sep 15, 2025 at 08:58:35AM -0700, David Rientjes wrote: >>>>>> This week's topic will be kmemdump led by Eugen Hristev. See the latest >>>>>> proposal at https://lwn.net/Articles/1031319/. >>>>> >>>>> I don't understand what this has to do with mm, to be honest. >>>>> It looks like a debugging aid. >>>> >>>> It was suggested to move it to mm/ : >>>> >>>> https://lore.kernel.org/all/0fa9e4e7-1247-4c82-8c0b-fa65b7fbb56d@infradead.org/ >>> >>> I feel like you should be able to explain this rather better than >>> "somebody else told me to move it". As of this moment, I still don't >>> know what kmemdump even is. >>> >>>>> >>>>> https://lore.kernel.org/lkml/20250422113156.575971-2-eugen.hristev@linaro.org/ >>>>> >>>>> is a great example of how to write a lot of documentation that doesn't >>>>> actually tell the reader what anything is. >>>>> >>>>> >>>> >>>> Here is a link to the v3 where I changed it a little bit : >>>> >>>> https://lore.kernel.org/all/20250912150855.2901211-1-eugen.hristev@linaro.org/ >>>> >>>> I am eager to improve the documentation to make more sense out of it, I >>>> am happy with suggestions. >>> >>> Start by telling me what it is. >> >> A way to select memory areas from the kernel that can be used to debug >> the kernel, instead of saving the whole memory dump which is mostly not >> of interest and takes a lot of space. >> Anyone can register a pointer and a size, these are placed into a list, >> and a dedicated firmware can parse it and save it in case of a crash. >> Does this make sense ? > > Is it only for kernel or is available for userspace as well? And the > crashes here, we are talking about kernel crashes or includes process > crashes as well? Using the crash tool, you can inspect the tasks, current task and other tasks. You could see the processes and current context. kmemdump can be used to select also user space regions. So I suppose you can dump that, but the crash tool would be specifically used for kernel debugging. I have not attempted this though. It is interesting to see how it could work. Maybe kmemdump could create a coredump of a running process, but it's not attempted as of now.