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 DC48C4A1DFB for ; Mon, 12 Oct 2026 17:11:22 +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=1791825084; cv=none; b=g+caIu0z2mFBG7KmttJ3PaA3NNf/cbms9WnQJhfgDEScAeLVzdfGAKs1xOeWGoy7u0VEM7u1+XpnSmfXGDFGqIpZUswO8VPeh1ZdNsgZVNxCj+MMJL3w/YFjQwHjK/PO0kslThdNr0C2YZmBPeS5NMFvuQxtoG6rpz17kzQhNz0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791825084; c=relaxed/simple; bh=NyXOCQz0IHMV+KX1ZnDo8YCjMKOponZ8LmuUVuhrrFg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QED7WByS+N/mRW0ENA44gBVev0RzTP26bw9nEWigFUjif7IHGbvMrIJ5Hucg80l19UgnXE/QHbeYpK07jVx1NaM03uEfTiIchmVv1KWr3OlFhCSIOtyVZ4iUUSluGMMGG3Nnpwr4wATvEGQMptwPjpp9hbCkmGfSa8sfuWFkNPk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i9yb8Aru; 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="i9yb8Aru" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 452741F0089C; Mon, 12 Oct 2026 17:11:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791825082; bh=eIpXBxc1Zh+5tYOYTOcIg/Ba6/+mSunX8M4pzhxilnw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=i9yb8AruVWhFnaBylkZ3cCIq17GgdHNPTtRN/iIoerfLgW5ZLo57/VPpwKXuTXpX9 Rxqv6XA8bqubOEVIZ66EY4jsNKQP6dsMn5011o4a9WCImjqbGvlBj4xK5AaVrf9Dw5 L4ZbFwjbTLxhk9coLPjuPVFKyMMLSNCGbA+zXpkbdeW5YeRe7GVGiArf1Sad+EA5dw N1gI/wrGWHCZFNKNzRFGKqQkuyrK80Fu14ktFl9La2Bv5kRdsKUQQOoSps/8oaxzWn COJjN6dXrswLvINJaSw35/yg/vS+E9oOkIE58zsgJLAGfsPBYTdfctD/24yKKPFym2 WN/sATU+rv9bw== Date: Mon, 12 Oct 2026 20:11:10 +0300 From: Mike Rapoport To: Pratyush Yadav Cc: Sourabh Jain , kexec@lists.infradead.org, Alexander Graf , Andrew Morton , George Guo , Pasha Tatashin , "Ritesh Harjani (IBM)" , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] kho: fix global scratch size calculation Message-ID: References: <20260922131217.698809-1-sourabhjain@linux.ibm.com> <2vxzo6czjaa9.fsf@kernel.org> 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: <2vxzo6czjaa9.fsf@kernel.org> On Mon, Oct 12, 2026 at 03:52:46PM +0200, Pratyush Yadav wrote: > On Sat, Oct 03 2026, Mike Rapoport wrote: > > > On Tue, Sep 22, 2026 at 06:42:16PM +0530, Sourabh Jain wrote: > >> KHO calculates the global scratch size based on memblock-reserved kernel > >> memory. It passes NUMA_NO_NODE to memblock_reserved_kern_size() for > >> this calculation. > >> > >> When memblock_reserved_kern_size() is called with NUMA_NO_NODE, it > >> counts both: > >> > >> - memory reserved for a specific NUMA node > >> - memory reserved with NUMA_NO_NODE > >> > >> KHO needs to distinguish between these two types of reservations. > >> When calculating the size of global scratch memory, KHO only needs to > >> account for reservations made with NUMA_NO_NODE. Reservations made for > >> a specific NUMA node must not be included in the global scratch size. > >> > >> Add memblock_reserved_size_nid() to calculate reserved memory for a > >> given reservation type and NUMA node. When NUMA_NO_NODE is passed, it > >> counts only memory reserved with NUMA_NO_NODE. > >> > >> Use the new API for lowmem, global, and per-node KHO scratch size > >> calculations. For lowmem and global scratch, count only memory > >> reservations that were made with NUMA_NO_NODE. For per-node scratch, > >> count only memory reservations that were made with the corresponding > >> NUMA node ID. > >> > >> Remove memblock_reserved_hugetlb_size() since it has the same > >> implementation as the new API and differs only in the memblock > >> reservation flag being checked. The new API handles both kernel and > >> HugeTLB reservations through its reservation type argument. > >> > >> Define the new helper as a static function in the KHO implementation, > >> since it is only used by KHO and has no users outside > >> kernel/liveupdate/kexec_handover.c. > > > > I looked again and this feels like a band-aid to me. > > > > I think we need to step back and rethink the order of the > > scratch/kho-bootmem sizing and consider how NUMA and lowmem are involved > > there. > > Could you elaborate? How else would you calculate the sizes? > > To me, the idea sounds fine (although I also share your comments on the > code style). This is what the global scratch size should have been doing > from the get-go. Today it over-allocates by counting both global > allocations and _all_ per-node allocations. > There is a separate problem with CONFIG_NUMA=n, but for that I think we > should just have a different allocation path where we only do lowmem and > global scratch. I mean more fundamental code refactoring that takes into the account all cases (and I could miss some) - NUMA vs no-NUMA - systems that have global scratch containing lowmem scratch vs those that don't - and of course fix global scratch over-allocation > >> On powerpc, the difference can be seen in the scratch_len values > >> reported by: > >> > >> cat /sys/kernel/debug/kho/out/scratch_len > >> > >> Before this change, the global scratch allocation was 0x12000000 > >> (288 MB): > >> > >> 0x1000000 (16 MB) > >> 0x12000000 (288 MB) <- global allocation > >> 0x5000000 (80 MB) > >> > >> After this change, the global scratch allocation is 0xd000000 > >> (208 MB): > >> > >> 0x1000000 (16 MB) > >> 0xd000000 (208 MB) <- global allocation > >> 0x5000000 (80 MB) > >> > >> The 80 MB difference is the per-node reservation that was previously > >> being included in the global allocation. > >> > >> The same issue also affects lowmem scratch memory, but its impact is > >> limited because the lowmem scratch memory calculation is restricted to > >> the first 4G of memory. The changes also cover the lowmem scratch > >> memory case. > >> > >> Cc: Alexander Graf > >> Cc: Andrew Morton > >> Cc: George Guo > >> Cc: Mike Rapoport > >> Cc: Pasha Tatashin > >> Cc: Pratyush Yadav > >> Cc: Ritesh Harjani (IBM) > >> Cc: linux-kernel@vger.kernel.org > >> Cc: linux-mm@kvack.org > >> Signed-off-by: Sourabh Jain > [...] > > -- > Regards, > Pratyush Yadav -- Sincerely yours, Mike.