From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DFB62606A326 for ; Tue, 3 Nov 2026 14:14:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=TH3DFZ55; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aaxGzOap DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: Message-ID:Date:References:In-Reply-To:Subject:Cc:To:From:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=2V/ndYvkVxA79d43Mf+7vdJDqWuLHWGgjyn9NcOP058=; b=TH3DFZ55bnJf+ioC8aSUzeZ0+0 9f5LGuJDRH2d2NWcr5dezYUcHp6rcUHiJkzYG/F7MTrz1lImSKsssQ1jBrPNKQ/gdS63rmCPIai0p Kbaq56Cnp1GtIu/Z1SWD168v++Nb8VbIm0GBIQunMzwwdvhgp2yVPJdTGvAyqYF5LYcPswUigQU9u AQ7Jlti3gXwFBrnBLqFJSWlk2jfo8D+yN7trwm3gPH/ykC6SukKgqBZNSFNEKixWM7y0HKYZbon8a iFQlvgEbCLiW2/6aK5XTRazWL56J0MHCdFOMJg1gvwIIrEue+K5VmPKCGc3a5x+GIf0Yn2wLmHLTL BCrDiAaQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOFHe-00000002gpU-2Z1S; Tue, 03 Nov 2026 14:14:42 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xOFHd-00000002gpE-1gBr for kexec@lists.infradead.org; Tue, 03 Nov 2026 14:14:41 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 39E136020A; Tue, 3 Nov 2026 14:14:40 +0000 (UTC) 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-Archived-By: MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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