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[PATCH] kho: skip memoryless NUMA nodes when reserving scratch areas

Evangelos Petrongonas posted 1 patch 3 weeks, 1 day ago
There is a newer version of this series
kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)
[PATCH] kho: skip memoryless NUMA nodes when reserving scratch areas
Posted by Evangelos Petrongonas 3 weeks, 1 day ago 
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 introducing kho_mem_nodes_count() which counts only 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>
---
 kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 9dc51fab604f..c970ed08b477 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -623,6 +623,23 @@ static phys_addr_t __init scratch_size_node(int nid)
 	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
 }
 
+/*
+ * Count online NUMA nodes that have memory. Memoryless nodes cannot have
+ * scratch memory and should be excluded.
+ */
+static unsigned int __init kho_mem_nodes_count(void)
+{
+	unsigned int cnt = 0;
+	int nid;
+
+	for_each_online_node(nid) {
+		if (node_state(nid, N_MEMORY))
+			cnt++;
+	}
+
+	return cnt;
+}
+
 /**
  * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
  *
@@ -643,7 +660,7 @@ 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 = kho_mem_nodes_count() + 2;
 	size = kho_scratch_cnt * sizeof(*kho_scratch);
 	kho_scratch = memblock_alloc(size, PAGE_SIZE);
 	if (!kho_scratch)
@@ -674,6 +691,10 @@ static void __init kho_reserve_scratch(void)
 	i++;
 
 	for_each_online_node(nid) {
+		/* Skip memoryless nodes - we cannot allocate scratch memory there */
+		if (!node_state(nid, N_MEMORY))
+			continue;
+
 		size = scratch_size_node(nid);
 		addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
 						0, MEMBLOCK_ALLOC_ACCESSIBLE,
-- 
2.43.0




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Re: [PATCH] kho: skip memoryless NUMA nodes when reserving scratch areas
Posted by Pratyush Yadav 3 weeks, 1 day ago 
Hi Evangelos,

On Fri, Jan 16 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 introducing kho_mem_nodes_count() which counts only 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>
> ---
>  kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 9dc51fab604f..c970ed08b477 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -623,6 +623,23 @@ static phys_addr_t __init scratch_size_node(int nid)
>  	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
>  }
>  
> +/*
> + * Count online NUMA nodes that have memory. Memoryless nodes cannot have
> + * scratch memory and should be excluded.
> + */
> +static unsigned int __init kho_mem_nodes_count(void)
> +{
> +	unsigned int cnt = 0;
> +	int nid;
> +
> +	for_each_online_node(nid) {
> +		if (node_state(nid, N_MEMORY))
> +			cnt++;
> +	}
> +
> +	return cnt;
> +}
> +

You don't need this. You can use nodes_weight(nodes_state[N_MEMORY])
directly. Other than this, LGTM.

>  /**
>   * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
>   *
> @@ -643,7 +660,7 @@ 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 = kho_mem_nodes_count() + 2;
>  	size = kho_scratch_cnt * sizeof(*kho_scratch);
>  	kho_scratch = memblock_alloc(size, PAGE_SIZE);
>  	if (!kho_scratch)
> @@ -674,6 +691,10 @@ static void __init kho_reserve_scratch(void)
>  	i++;
>  
>  	for_each_online_node(nid) {
> +		/* Skip memoryless nodes - we cannot allocate scratch memory there */
> +		if (!node_state(nid, N_MEMORY))
> +			continue;
> +
>  		size = scratch_size_node(nid);
>  		addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
>  						0, MEMBLOCK_ALLOC_ACCESSIBLE,

-- 
Regards,
Pratyush Yadav
Re: [PATCH] kho: skip memoryless NUMA nodes when reserving scratch areas
Posted by Mike Rapoport 2 weeks, 6 days ago 
On Fri, Jan 16, 2026 at 11:57:14AM +0000, Pratyush Yadav wrote:
> Hi Evangelos,
> 
> On Fri, Jan 16 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 introducing kho_mem_nodes_count() which counts only 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>
> > ---
> >  kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++-
> >  1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> > index 9dc51fab604f..c970ed08b477 100644
> > --- a/kernel/liveupdate/kexec_handover.c
> > +++ b/kernel/liveupdate/kexec_handover.c
> > @@ -623,6 +623,23 @@ static phys_addr_t __init scratch_size_node(int nid)
> >  	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
> >  }
> >  
> > +/*
> > + * Count online NUMA nodes that have memory. Memoryless nodes cannot have
> > + * scratch memory and should be excluded.
> > + */
> > +static unsigned int __init kho_mem_nodes_count(void)
> > +{
> > +	unsigned int cnt = 0;
> > +	int nid;
> > +
> > +	for_each_online_node(nid) {
> > +		if (node_state(nid, N_MEMORY))
> > +			cnt++;
> > +	}
> > +
> > +	return cnt;
> > +}
> > +
> 
> You don't need this. You can use nodes_weight(nodes_state[N_MEMORY])
> directly. Other than this, LGTM.
> 
> >  /**
> >   * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
> >   *
> > @@ -643,7 +660,7 @@ 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 = kho_mem_nodes_count() + 2;
> >  	size = kho_scratch_cnt * sizeof(*kho_scratch);
> >  	kho_scratch = memblock_alloc(size, PAGE_SIZE);
> >  	if (!kho_scratch)
> > @@ -674,6 +691,10 @@ static void __init kho_reserve_scratch(void)
> >  	i++;
> >  
> >  	for_each_online_node(nid) {
> > +		/* Skip memoryless nodes - we cannot allocate scratch memory there */
> > +		if (!node_state(nid, N_MEMORY))
> > +			continue;
> > +

And here you can use 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,
> 
> -- 
> Regards,
> Pratyush Yadav

-- 
Sincerely yours,
Mike.

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