From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 690601AAE28; Mon, 10 Aug 2026 08:24:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786350247; cv=none; b=qjHyM4L7rdpvOq/9WwOMC6f4ZuhGDNhLp+Gda8CKZJXusl6NIRAkm32bwcntmZx7H654rQTeeeuDK562/MDsK32YEQoe7tUZpS/EPQ/XoD37JMGLqp3HvoHyzQig0L0B3aLZLa5xf4eDr8NrTZT6NBCPdn9YWZT6TWLKgZP2yps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786350247; c=relaxed/simple; bh=udpzQOnp2NHd3xagHK7GnNYaIbSRI46MyJU+yjjkzVE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DMmkpyC8bCECfRVp3hEPYOHqVs5LRRh7EyBpx5jfCJbqQUMIJ2kJXpfevDX5ej0U81pGDyLE5x4TqRrQ9Rq913u4+d+o7TxlMd9NUZmfMaJLdJ7vqKcEA43jjBxV+0Oahuxl9WDjeWAt7Oza4UG83gVe4wQ00Dhwh8lyu89QQuc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kDf0pMZ6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kDf0pMZ6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3ABA1F000E9; Mon, 10 Aug 2026 08:24:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786350246; bh=za/dgLTVAKpnAfno98BQIXcUPCYXTejUD5HWiea1RH4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; 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> 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: <20260803193938.8778-1-maxi.saparov@gmail.com> 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.