* Re: [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas
2026-01-20 17:59 [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas Evangelos Petrongonas
@ 2026-01-20 18:37 ` Pratyush Yadav
2026-01-20 19:00 ` Mike Rapoport
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Pratyush Yadav @ 2026-01-20 18:37 UTC (permalink / raw)
To: Evangelos Petrongonas
Cc: Mike Rapoport, Pasha Tatashin, Pratyush Yadav, Alexander Graf,
Jason Miu, linux-kernel, kexec, linux-mm, nh-open-source
On Tue, Jan 20 2026, Evangelos Petrongonas wrote:
> kho_reserve_scratch() iterates over all online NUMA nodes to allocate
> per-node scratch memory. On systems with memoryless NUMA nodes (nodes
> that have CPUs but no memory), memblock_alloc_range_nid() fails because
> there is no memory available on that node. This causes KHO initialization
> to fail and kho_enable to be set to false.
>
> Some ARM64 systems have NUMA topologies where certain nodes contain only
> CPUs without any associated memory. These configurations are valid and
> should not prevent KHO from functioning.
>
> Fix this by only counting nodes that have memory (N_MEMORY state) and
> skip memoryless nodes in the per-node scratch allocation loop.
>
> Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
[...]
--
Regards,
Pratyush Yadav
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas
2026-01-20 17:59 [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas Evangelos Petrongonas
2026-01-20 18:37 ` Pratyush Yadav
@ 2026-01-20 19:00 ` Mike Rapoport
2026-01-22 18:18 ` Pasha Tatashin
2026-01-22 23:21 ` Andrew Morton
3 siblings, 0 replies; 6+ messages in thread
From: Mike Rapoport @ 2026-01-20 19:00 UTC (permalink / raw)
To: Evangelos Petrongonas
Cc: Pasha Tatashin, Pratyush Yadav, Alexander Graf, Jason Miu,
linux-kernel, kexec, linux-mm, nh-open-source
On Tue, Jan 20, 2026 at 05:59:11PM +0000, Evangelos Petrongonas wrote:
> kho_reserve_scratch() iterates over all online NUMA nodes to allocate
> per-node scratch memory. On systems with memoryless NUMA nodes (nodes
> that have CPUs but no memory), memblock_alloc_range_nid() fails because
> there is no memory available on that node. This causes KHO initialization
> to fail and kho_enable to be set to false.
>
> Some ARM64 systems have NUMA topologies where certain nodes contain only
> CPUs without any associated memory. These configurations are valid and
> should not prevent KHO from functioning.
>
> Fix this by only counting nodes that have memory (N_MEMORY state) and
> skip memoryless nodes in the per-node scratch allocation loop.
>
> Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> v2:
> - Removed kho_mem_nodes_count in favour of nodes_weight(nodes_state[N_MEMORY])
> - Use for_each_node_state(nid, N_MEMORY) to loop over nodes that are both
> online and have memory.
> TIL: Nodes in N_MEMORY are a subset of those that are online. Thanks Mike :)
>
> kernel/liveupdate/kexec_handover.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 9dc51fab604f..979ebaf015bf 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -643,7 +643,7 @@ static void __init kho_reserve_scratch(void)
> scratch_size_update();
>
> /* FIXME: deal with node hot-plug/remove */
> - kho_scratch_cnt = num_online_nodes() + 2;
> + kho_scratch_cnt = nodes_weight(node_states[N_MEMORY]) + 2;
> size = kho_scratch_cnt * sizeof(*kho_scratch);
> kho_scratch = memblock_alloc(size, PAGE_SIZE);
> if (!kho_scratch)
> @@ -673,7 +673,11 @@ static void __init kho_reserve_scratch(void)
> kho_scratch[i].size = size;
> i++;
>
> - for_each_online_node(nid) {
> + /*
> + * Loop over nodes that have both memory and are online. Skip
> + * memoryless nodes, as we can not allocate scratch areas there.
> + */
> + for_each_node_state(nid, N_MEMORY) {
> size = scratch_size_node(nid);
> addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
> 0, MEMBLOCK_ALLOC_ACCESSIBLE,
> --
> 2.43.0
>
>
>
>
> Amazon Web Services Development Center Germany GmbH
> Tamara-Danz-Str. 13
> 10243 Berlin
> Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
> Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
> Sitz: Berlin
> Ust-ID: DE 365 538 597
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas
2026-01-20 17:59 [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas Evangelos Petrongonas
2026-01-20 18:37 ` Pratyush Yadav
2026-01-20 19:00 ` Mike Rapoport
@ 2026-01-22 18:18 ` Pasha Tatashin
2026-01-22 23:21 ` Andrew Morton
3 siblings, 0 replies; 6+ messages in thread
From: Pasha Tatashin @ 2026-01-22 18:18 UTC (permalink / raw)
To: Evangelos Petrongonas
Cc: Mike Rapoport, Pratyush Yadav, Alexander Graf, Jason Miu,
linux-kernel, kexec, linux-mm, nh-open-source
On Tue, Jan 20, 2026 at 12:59 PM Evangelos Petrongonas
<epetron@amazon.de> wrote:
>
> kho_reserve_scratch() iterates over all online NUMA nodes to allocate
> per-node scratch memory. On systems with memoryless NUMA nodes (nodes
> that have CPUs but no memory), memblock_alloc_range_nid() fails because
> there is no memory available on that node. This causes KHO initialization
> to fail and kho_enable to be set to false.
>
> Some ARM64 systems have NUMA topologies where certain nodes contain only
> CPUs without any associated memory. These configurations are valid and
> should not prevent KHO from functioning.
>
> Fix this by only counting nodes that have memory (N_MEMORY state) and
> skip memoryless nodes in the per-node scratch allocation loop.
>
> Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
> ---
> v2:
> - Removed kho_mem_nodes_count in favour of nodes_weight(nodes_state[N_MEMORY])
> - Use for_each_node_state(nid, N_MEMORY) to loop over nodes that are both
> online and have memory.
> TIL: Nodes in N_MEMORY are a subset of those that are online. Thanks Mike :)
>
> kernel/liveupdate/kexec_handover.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 9dc51fab604f..979ebaf015bf 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -643,7 +643,7 @@ static void __init kho_reserve_scratch(void)
> scratch_size_update();
>
> /* FIXME: deal with node hot-plug/remove */
> - kho_scratch_cnt = num_online_nodes() + 2;
> + kho_scratch_cnt = nodes_weight(node_states[N_MEMORY]) + 2;
> size = kho_scratch_cnt * sizeof(*kho_scratch);
> kho_scratch = memblock_alloc(size, PAGE_SIZE);
> if (!kho_scratch)
> @@ -673,7 +673,11 @@ static void __init kho_reserve_scratch(void)
> kho_scratch[i].size = size;
> i++;
>
> - for_each_online_node(nid) {
> + /*
> + * Loop over nodes that have both memory and are online. Skip
> + * memoryless nodes, as we can not allocate scratch areas there.
> + */
> + for_each_node_state(nid, N_MEMORY) {
> size = scratch_size_node(nid);
> addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
> 0, MEMBLOCK_ALLOC_ACCESSIBLE,
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas
2026-01-20 17:59 [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas Evangelos Petrongonas
` (2 preceding siblings ...)
2026-01-22 18:18 ` Pasha Tatashin
@ 2026-01-22 23:21 ` Andrew Morton
2026-01-23 8:53 ` Mike Rapoport
3 siblings, 1 reply; 6+ messages in thread
From: Andrew Morton @ 2026-01-22 23:21 UTC (permalink / raw)
To: Evangelos Petrongonas
Cc: Mike Rapoport, Pasha Tatashin, Pratyush Yadav, Alexander Graf,
Jason Miu, linux-kernel, kexec, linux-mm, nh-open-source
On Tue, 20 Jan 2026 17:59:11 +0000 Evangelos Petrongonas <epetron@amazon.de> wrote:
> kho_reserve_scratch() iterates over all online NUMA nodes to allocate
> per-node scratch memory. On systems with memoryless NUMA nodes (nodes
> that have CPUs but no memory), memblock_alloc_range_nid() fails because
> there is no memory available on that node. This causes KHO initialization
> to fail and kho_enable to be set to false.
>
> Some ARM64 systems have NUMA topologies where certain nodes contain only
> CPUs without any associated memory. These configurations are valid and
> should not prevent KHO from functioning.
>
> Fix this by only counting nodes that have memory (N_MEMORY state) and
> skip memoryless nodes in the per-node scratch allocation loop.
>
So kho is unusable on such machines.
Should we backport this? I'm thinking
Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers").
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] kho: skip memoryless NUMA nodes when reserving scratch areas
2026-01-22 23:21 ` Andrew Morton
@ 2026-01-23 8:53 ` Mike Rapoport
0 siblings, 0 replies; 6+ messages in thread
From: Mike Rapoport @ 2026-01-23 8:53 UTC (permalink / raw)
To: Andrew Morton
Cc: Evangelos Petrongonas, Pasha Tatashin, Pratyush Yadav,
Alexander Graf, Jason Miu, linux-kernel, kexec, linux-mm,
nh-open-source
On Thu, Jan 22, 2026 at 03:21:12PM -0800, Andrew Morton wrote:
> On Tue, 20 Jan 2026 17:59:11 +0000 Evangelos Petrongonas <epetron@amazon.de> wrote:
>
> > kho_reserve_scratch() iterates over all online NUMA nodes to allocate
> > per-node scratch memory. On systems with memoryless NUMA nodes (nodes
> > that have CPUs but no memory), memblock_alloc_range_nid() fails because
> > there is no memory available on that node. This causes KHO initialization
> > to fail and kho_enable to be set to false.
> >
> > Some ARM64 systems have NUMA topologies where certain nodes contain only
> > CPUs without any associated memory. These configurations are valid and
> > should not prevent KHO from functioning.
> >
> > Fix this by only counting nodes that have memory (N_MEMORY state) and
> > skip memoryless nodes in the per-node scratch allocation loop.
> >
>
> So kho is unusable on such machines.
>
> Should we backport this? I'm thinking
>
> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers").
It's only for v6.18, but sure, why not.
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 6+ messages in thread