From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793715280; b=06ZDXWq25pet2dOY1u1SUWnvN6moIoV1TqQdhVMbMjpAqaWms2gAhUeGDnljKwxIUjHP QvgYCc1nPXk49HgVVJMoYrzzjTDWmfobFYejgNEjOPuUgaq60o0M7j/NpVvgoLrJmVk60 RGQ+exbUF8AZPxengA4ezt2rvWXz35IAkDnNn9hdsY8iBzEK/qRN50JYSWKCKNwJDQhvs gng47VlzbGQ1bl6yVrHEUN0hLEiIHviuV3Q1W/u8H9jTLfHYhVoPYzR/1cTIvnigiO74A xf/UYOjEApTOqMPJ1OBAu6jHXzEJnEiTKugoqyHtCyTr7/C1cKF5ULgvxoggrBzXCFg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793715280; h=Received:DKIM-Signature:From:To:Cc:Subject:In-Reply-To:References: Date:Message-ID:User-Agent:MIME-Version:Content-Type; bh=2V/ndYvkVxA79d43Mf+7vdJDqWuLHWGgjyn9NcOP058=; b=ZaxyMNIyKkzh14DHUNrpIKvbueyuGJoSiKJT7KhZahd8p+PwZq6ssD04WOdpVgummnmV Dy+MGkVosHX4v4IX0NmiM7UvzZhUDFK3RA3gkZ1lsMNittLnRCBFpOQIyzVbAtQLFxvF8 egia4WTgw86ez6b80pIuUbwTblIns0dWOKekGrX5wBBVnxRuwOC7UvR9KhrwNES5Jofhd 7/m/ADLSGoCxb9g6sTca2BrwcKAXQc6327OYnWzi9Yzve/qDnACrQeDWVbVBfS4ZSb5JZ W6tm5XQ0mK+h8R7nRHRzp/REjhLUmN3x6MS8yRZ1DbuXb6B4fJ47ilFhLjdG66EyZuQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aaxGzOap; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 61562606A326 for ; Tue, 3 Nov 2026 14:14:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aaxGzOap Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0AE71F000C1; Tue, 3 Nov 2026 14:14:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793715279; bh=2V/ndYvkVxA79d43Mf+7vdJDqWuLHWGgjyn9NcOP058=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=aaxGzOapyHfFlHAjXCCWCjylt3vC/AQ1UNK9BFKFXitIBtPZrbR/XMTiI3H58/9B3 rm4qwhVZkPr9afPfqC+SFSfDnkPN/4pEHVC1sK4quxxp1Rc5hVPXwC3DOw6tsidh9H MFXS5kQySyEbKY0PlI8frUlR0NraysItCxrW/vRVEkyB7L9oRSQz4l6B9ikb/ZLeqH e9UYc9Xglp9TUTDi2YQU+w++JAwJxwGWJQF6La9NcirxdMEI7eyWYBWmUXQ376ZAlr nkMeyLqyu6kO0wR8Sh0e85LlWSp4vP1DPz82PnnY3yl2gSyJfBzbsZEp02Z5x51mnz 3UduQA6+/qHHw== From: Pratyush Yadav To: "Mike Rapoport (Microsoft)" Cc: Pasha Tatashin , Pratyush Yadav , Alexander Graf , Andrew Morton , Chen Pei , George Guo , Kexin Liu , Sourabh Jain , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/2] kho: skip zero-sized lowmem and global bootmem areas In-Reply-To: <20261103-kho-bootmem-sizing-v1-1-45aa74098f34@kernel.org> (Mike Rapoport's message of "Tue, 03 Nov 2026 13:49:49 +0200") References: <20261103-kho-bootmem-sizing-v1-0-45aa74098f34@kernel.org> <20261103-kho-bootmem-sizing-v1-1-45aa74098f34@kernel.org> Date: Tue, 03 Nov 2026 15:14:36 +0100 Message-ID: <2vxza4nqm27n.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain Hi Mike, On Tue, Nov 03 2026, Mike Rapoport (Microsoft) wrote: > The lowmem and the global bootmem areas can have zero size, for example > when none or all of the memory is below ARCH_LOW_ADDRESS_LIMIT, or when > either of those areas is explicitly set to zero with kho_bootmem=. > > For a zero-sized allocation memblock returns an address without reserving > anything, and that empty area is recorded in kho_bootmem. If there is no > memory below ARCH_LOW_ADDRESS_LIMIT, allocation of the empty lowmem area > fails and KHO gets disabled. > > Extract a helper that checks for zero size and allocates memory from > memblock, and use it to skip empty areas the same way as empty per-node > areas are skipped. > > Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers") > Reported-by: Chen Pei > Closes: https://lore.kernel.org/all/20261026131851.9942-1-cp0613@linux.alibaba.com > Signed-off-by: Mike Rapoport (Microsoft) Thanks for the patch! LGTM for the most part, one minor nitpick below. > --- > kernel/liveupdate/kexec_handover.c | 61 ++++++++++++++++++-------------------- > 1 file changed, 29 insertions(+), 32 deletions(-) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 6f1f55fe31819..f268c57413a7e 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -820,6 +820,27 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size) > return false; > } > > +static int __init kho_reserve_bootmem_area(int *idx, phys_addr_t size, > + phys_addr_t end, int nid) > +{ > + phys_addr_t addr; > + int i = *idx; > + > + if (!size) > + return 0; > + > + addr = memblock_alloc_range_nid(size, BOOTMEM_ALIGNMENT_BYTES, 0, end, > + nid, true); > + if (!addr) > + return -ENOMEM; > + > + kho_bootmem[i].addr = addr; > + kho_bootmem[i].size = size; > + *idx = i + 1; > + > + return 0; I reckon it will be cleaner if you update kho_bootmem_cnt here directly. So you directly do: kho_bootmem[kho_bootmem_cnt].addr = addr; kho_bootmem[kho_bootmem_cnt].size = size; kho_bootmem_cnt++; You won't have to pass around *idx and you won't need the final kho_bootmem_cnt assignment. You might also want to have a kho_bootmem_max_cnt and do some bounds checking here. What do you think? > +} > + > /** > * kho_reserve_bootmem - Reserve a contiguous chunk of memory for kexec > * > @@ -832,7 +853,7 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size) > static void __init kho_reserve_bootmem(void) > { > int nid, i = 0, max_nr_bootmem; > - phys_addr_t addr, size; > + phys_addr_t size; > > if (!kho_enable) > return; > @@ -852,56 +873,32 @@ static void __init kho_reserve_bootmem(void) > * reserve bootmem area in low memory for lowmem allocations in the > * next kernel > */ > - size = bootmem_size_lowmem; > - addr = memblock_phys_alloc_range(size, BOOTMEM_ALIGNMENT_BYTES, 0, > - ARCH_LOW_ADDRESS_LIMIT); > - if (!addr) { > + if (kho_reserve_bootmem_area(&i, bootmem_size_lowmem, > + ARCH_LOW_ADDRESS_LIMIT, NUMA_NO_NODE)) { > pr_err("Failed to reserve lowmem bootmem\n"); > goto err_free_bootmem_desc; > } > > - kho_bootmem[i].addr = addr; > - kho_bootmem[i].size = size; > - i++; > - > /* reserve large contiguous area for allocations without nid */ > - size = bootmem_size_global; > - addr = memblock_phys_alloc(size, BOOTMEM_ALIGNMENT_BYTES); > - if (!addr) { > + if (kho_reserve_bootmem_area(&i, bootmem_size_global, > + MEMBLOCK_ALLOC_ACCESSIBLE, NUMA_NO_NODE)) { > pr_err("Failed to reserve global bootmem\n"); > goto err_free_bootmem_areas; > } > > - kho_bootmem[i].addr = addr; > - kho_bootmem[i].size = size; > - i++; > - > /* > * Loop over nodes that have both memory and are online. Skip > * memoryless nodes, as we can not allocate bootmem areas there. > */ > for_each_node_state(nid, N_MEMORY) { > - size = bootmem_size_node(nid); > - if (!size) > - continue; > - > - addr = memblock_alloc_range_nid(size, BOOTMEM_ALIGNMENT_BYTES, > - 0, MEMBLOCK_ALLOC_ACCESSIBLE, > - nid, true); > - if (!addr) { > + if (kho_reserve_bootmem_area(&i, bootmem_size_node(nid), > + MEMBLOCK_ALLOC_ACCESSIBLE, nid)) { > pr_err("Failed to reserve nid %d bootmem\n", nid); > goto err_free_bootmem_areas; > } > - > - kho_bootmem[i].addr = addr; > - kho_bootmem[i].size = size; > - i++; > } > > - /* > - * Nodes that needed no bootmem were skipped, so fewer areas than > - * initially estimated may have been reserved. > - */ > + /* Areas with zero size were skipped */ > kho_bootmem_cnt = i; > > return; -- Regards, Pratyush Yadav