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b=PzQFw0FctCGUG1qHhQ27pa7aqyd7BxJUFvbnrW/uv19RT1NEp+QBsPx9tWUT0MRKZ EP/IgnjNU2qQXaN6ydBSAjnVmbibh1JigkN4pF0k4b4TVFlN6vXgsHaMIv4OLWjbtW 9JZAxCVdX8vntYR8F2GsWdf0v+5nIZntQeHoeycoXS6Lh2ud8VSmqn3XOp3F5vl6Gk 1UEiBKOXa+yKIeI0dmRVCCjCuoSXB1eQLxtei9hnz4GTO95SjGcSospGRBVSQlJ3qW ekL/wjVM9kPF4GBBy0057j6cy9SYv1Kl52peqE0i5VtsYdAP5nRfejwHQD75bTPkD2 5zQx0FPWv/hpg== Date: Wed, 4 Nov 2026 13:22:22 +0200 From: Mike Rapoport To: Pasha Tatashin Cc: 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 Message-ID: References: <20261103-kho-bootmem-sizing-v1-0-45aa74098f34@kernel.org> <20261103-kho-bootmem-sizing-v1-1-45aa74098f34@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7C98EC0002 X-Stat-Signature: m78gdjxsdautgw7hjxb8kts3xa8gsm8m X-Rspam-User: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-HE-Tag: 1793791351-212373 X-HE-Meta: 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 LLH3zHRX qALhIVLL0BzsAm/tkIH2qkUmjOy2KPxmOCcGDO302oDwmoZ0BjMi4NQlcJSBgqdulqZ0ID7cVUre2QQ+vLgFM9pA+fuIOdNl1o44xSI82WtSCyCrhd3FubHQaLlHpNWO1jbuFB/KCueGTWy8W0S0LK7UY9reEbVCpS6zzj/tukHTDoR68gJ/PNxGps5JZPU/71U6oG/WlGWRTX13rDCS4Pv2oTdFo4M0piDNF86Zz4AZ3dGKN9fA282BkMmdtzD5+yYEfPoaIo/Z74+SMu2PyD+0D2LUfDHndkIksTklGF5Tpi3Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 02:48:36PM -0500, Pasha Tatashin wrote: > On 11-03 13:49, 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) > > --- > > 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; > > +} > > + > > /** > > * 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"); > > You are adding a helper that returns an error code and then ignoring it > at all call sites. Even though it can only return -ENOMEM right now, > dropping the return value is not good practice. I don't think error code is important here. Even if some theoretical future update will change kho_reserve_bootmem_area() to return anything but -ENOMEM I don't see why the error code should be printed at all. And anyway, that would be the part of that change. -- Sincerely yours, Mike.