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[109.81.89.112]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-450d7fa2278sm12794105e9.12.2025.05.30.02.26.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 May 2025 02:26:07 -0700 (PDT) Date: Fri, 30 May 2025 11:26:06 +0200 From: Michal Hocko To: David Hildenbrand Cc: Baoquan He , Donald Dutile , Jiri Bohac , Vivek Goyal , Dave Young , kexec@lists.infradead.org, Philipp Rudo , Pingfan Liu , Tao Liu , linux-kernel@vger.kernel.org, David Hildenbrand Subject: Re: [PATCH v2 0/5] kdump: crashkernel reservation from CMA Message-ID: References: <04904e86-5b5f-4aa1-a120-428dac119189@redhat.com> <427fec88-2a74-471e-aeb6-a108ca8c4336@redhat.com> <04a49de5-eb79-431b-ba5b-eae2536781c6@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <04a49de5-eb79-431b-ba5b-eae2536781c6@redhat.com> On Fri 30-05-25 11:11:40, David Hildenbrand wrote: > On 30.05.25 11:07, Michal Hocko wrote: > > On Fri 30-05-25 10:39:39, David Hildenbrand wrote: > > > On 30.05.25 10:28, Michal Hocko wrote: > > [...] > > > > All that being said I would go with an additional parameter to the > > > > kdump cma setup - e.g. cma_sane_dma that would skip waiting and use 10s > > > > otherwise. That would make the optimized behavior opt in, we do not need > > > > to support all sorts of timeouts and also learn if this is not > > > > sufficient. > > > > > > > > Makes sense? > > > > > > Just so I understand correctly, you mean extending the "crashkernel=" option > > > with a boolean parameter? If set, e.g., wait 1s, otherwise magic number 10? > > > > crashkernel=1G,cma,cma_sane_dma # no wait on transition > > But is no wait ok? I mean, any O_DIRECT with any device would at least take > a bit, no? > > Of course, there is a short time between the crash and actually triggerying > kdump. This is something we can test for and if we need a short timeout in this case as well then it is just trivial to add it. I am much more concerned about those potentially unpredictable DMA transfers that could take too long and it is impossible to test for those and therefore we need to overshoot. > > crashkernel=1G,cma # wait on transition with e.g. 10s timeout > > In general, would work for me. > > -- > Cheers, > > David / dhildenb -- Michal Hocko SUSE Labs