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b=kDf0pMZ6OrhTueAr8AycS7nuhFdWoL9WvStErXhNm3cYqWa7kU6wjtfmC+OyLrVpv 4vcetwy4RP5rGzvLxz/ApRu7FEj2/8mu0Fh6OkbeAkVHL0lYg/YY1rtEXL3U34Y0TE h/SotQuCdSuIzeWasbGnrYi5yUA8CXqyCUUIcb96YUOQV1vHmzJa8E/I7DIdaXfJVH knYSokPq7zwOwZF+tta9poedyBEfuUZEQezEhdexuDZ9331hbNSKqpN/by80TRaAK7 2Br7Dnjo0gE0pQovl+l+bj5eaQqyd33PsRgF+ysKBRRemFMcwTWr4U33sHePjaQ7Mf j/Fiqqabfzcmw== Date: Mon, 10 Aug 2026 11:23:58 +0300 From: Mike Rapoport To: Maxi Saparov Cc: Pasha Tatashin , Pratyush Yadav , Alexander Graf , Evangelos Petrongonas , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, sdimitropoulos@coreweave.com, Maxi Saparov , stable@vger.kernel.org Subject: Re: [PATCH] kho: do not reserve scratch memory in the kdump kernel Message-ID: References: <20260803193938.8778-1-maxi.saparov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260803193938.8778-1-maxi.saparov@gmail.com> X-Stat-Signature: ujugirpd37s64s59bb3os1z8ekspzre1 X-Rspamd-Queue-Id: 75CCDA000A X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1786350247-55169 X-HE-Meta: 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 95yy+z1Q zK3enZvsJ1gfb40vLFZOlITjcrOV+X4Ao4bs5+mf3Yg64hDMeDLvK1wOf+s+w+QkgixDp5296EFHjh1rE7cbErznElU8yjHmr6/wMeflARkaaBCL6NJ9SaNh7WWqqlQfK4k7UUExWD3FWVzypYBETrMTt5FrRuSCxv3l/yXuAAyuSYaP+MsQwM0OYKSEK3iG1o2dlshbvZG1WlY3rlU4eLnrYayIlA4KOOqNxSRhYKDAUL5tNk7BBGCE3/p+ZplM5s0b4DI6Kz5frnR7dz0MROz0lrt62Ib2pvKCXzt7VKINLyjjDTYnK6e7fe4VMlQcSD8Ew9kGDq7i0xvaPOfhy0aVOJEcHYITTgdXSE9zXsGXCvcUJDNqH5NpZpwhmEzTc1aZr4sB2295mUfqdHD98weu8A0fqmK+V3BYZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, On Mon, Aug 03, 2026 at 03:39:38PM -0400, Maxi Saparov wrote: > From: Maxi Saparov > > If a kernel with CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y (or kho=on) > does not receive a handover FDT, it reserves KHO scratch memory in > kho_reserve_scratch(). The function computes the sizes from the early > memblock reservations of the kernel. The default scratch_scale is > 200%. The lowmem and global scratch areas each get twice the size of > the early reservations. Each NUMA node gets one more scratch area at > the same scale. > > The kdump kernel always takes this path. Since commit a6715d7ec472 > ("kho: skip KHO for crash kernel"), the kernel does not add KHO > metadata to the crash kimage. As a result, the kdump kernel never > receives a handover FDT and always reserves scratch memory. > > The kdump kernel boots in the small crashkernel= memory reservation. > On our x86 hosts, the kernel and initramfs make approximately 176 MB > of early reservations. The scratch areas then use approximately > 650 MB more of the crashkernel memory. When a large early allocation > fails, the kdump kernel panics: > > bio: can't create integrity buf pool > > A kdump kernel has nothing to hand over: its only task is to dump the > memory of the old kernel and reboot. Disable KHO in the kdump kernel > so that it does not reserve scratch memory. > > Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers") > Cc: stable@vger.kernel.org > Signed-off-by: Maxi Saparov > --- > kernel/liveupdate/kexec_handover.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 6fad9152387a..53b59edb5b36 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -12,6 +12,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -1636,6 +1637,9 @@ void __init kho_memory_init(void) > > if (kho_mem_retrieve(kho_get_fdt())) > kho_in.fdt_phys = 0; > + } else if (is_kdump_kernel()) { > + kho_enable = false; > + pr_info("disabled in the kdump kernel\n"); Can we put this on top as a separate if, like if (is_kdump_kernel()) { /* disable KHO */ return; } > } else { > kho_reserve_scratch(); > } > > base-commit: 3a0b8fa2eb36afc88b62a95f33f0c77c71fa5ded > -- > 2.55.0 > -- Sincerely yours, Mike.