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Piccoli" Cc: SeongJae Park , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, Andrew Morton , Mike Rapoport , Steven Rostedt Subject: Re: [PATCH v4 2/2] mm/memblock: Add reserve_mem debugfs info Date: Tue, 24 Mar 2026 18:24:23 -0700 Message-ID: <20260325012423.85658-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260324012839.1991765-2-gpiccoli@igalia.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 6E7C1140005 X-Stat-Signature: zj9yrqu5tgr1eaofrqxarzdbck78gjyk X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774401866-636810 X-HE-Meta: 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 1lZ2QPpy B/+He36290pnadz7GDPJwsOyQDge4okeXe6/J5ScIEwQ43qioIqOF8E7Orml3NHrMYz4Vpf42weAtROCRJIilqagdO0V4wuAGvfaVX6mtmOYZgOPKKTHf9rrO5DColjOT3xWXxwwXTPANypOHxH96onrnaP9q+Y2l8F8hyYIVWVeejweiQrTTeezxjDV4Pa7bwH1rvhIn0mY1APY+nvuTAowlGGmJYWj3eSt/SZee4vbo9OG3i4Fe2ePvcObNu7v7RW4yKO8yaj78eA3dlLjGxC3fuSW9PZm/O9wmx5FB44i1OVHMu+0iE0huRq6Bojukl58LJuthvE2+om5UWoSMrapWfaci0l/rjUoDpXFB7JkJW3aCRW1bblXjFybS52FM3s8GISWmEDni/ofs04UlU2odsXrTFDL5OYjP9fWcnTV86iVHCSc7x6qioDiD3NLJgvt4dfWRQ9QO/DbYnnAT/UnDMPnDej+qJuIy Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 23 Mar 2026 22:22:18 -0300 "Guilherme G. Piccoli" wrote: > When using the "reserve_mem" parameter, users aim at having an > area that (hopefully) persists across boots, so pstore infrastructure > (like ramoops module) can make use of that to save oops/ftrace logs, > for example. > > There is no easy way to determine if this kernel parameter is properly > set though; the kernel doesn't show information about this memory in > memblock debugfs, neither in /proc/iomem nor dmesg. This is a relevant > information for tools like kdumpst[0], to determine if it's reliable > to use the reserved area as ramoops persistent storage; checking only > /proc/cmdline is not sufficient as it doesn't tell if the reservation > effectively succeeded or not. > > Add here a new file under memblock debugfs showing properly set memory > reservations, with name and size as passed to "reserve_mem". Notice that > if no "reserve_mem=" is passed on command-line or if the reservation > attempts fail, the file is not created. > > [0] https://aur.archlinux.org/packages/kdumpst > > Cc: Andrew Morton > Cc: Mike Rapoport > Cc: Steven Rostedt > Cc: SeongJae Park > Signed-off-by: Guilherme G. Piccoli Reviewed-by: SeongJae Park Thanks, SJ [...]