[PATCH] memblock: use binary search to locate candidate regions

[PATCH] memblock: use binary search to locate candidate regions

[Tarun Sahu]

Use binary search (memblock_bsearch_start) in memblock_add_range() and
memblock_isolate_range() to locate candidate regions instead of linearly
scanning from index 0.

Under heavy memory fragmentation (such as KHO page preservation registering
hundreds of thousands of disjoint folios), scanning from index 0 on every
insertion and isolation results in O(N^2) complexity, causing boot-time
memory retrieval to take several minutes (~268s for 393k pages).

Using binary search reduces the worst-case complexity to O(N log N)
(and O(N) for sequential appends), cutting KHO memory retrieval time
from ~268s to ~50ms.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 mm/memblock.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 9ce86349a29f..88940474b020 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -160,6 +160,11 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
 	     i < memblock_type->cnt;					\
 	     i++, rgn = &memblock_type->regions[i])
 
+#define for_each_memblock_type_from(i, memblock_type, rgn, start)	\
+	for (i = (start), rgn = &memblock_type->regions[i];		\
+	     i < memblock_type->cnt;					\
+	     i++, rgn = &memblock_type->regions[i])
+
 #define memblock_dbg(fmt, ...)						\
 	do {								\
 		if (memblock_debug)					\
@@ -591,6 +596,33 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
 	type->total_size += size;
 }
 
+/**
+ * memblock_bsearch_start - Find the first region index where rend > base
+ * @type: memblock type to search
+ * @base: base physical address of the candidate range
+ *
+ * Returns the first region index that could potentially overlap @base.
+ */
+static int __init_memblock memblock_bsearch_start(struct memblock_type *type,
+						  phys_addr_t base)
+{
+	int mid, low = 0;
+	int high = type->cnt;
+
+	if (type->cnt && base >= type->regions[type->cnt - 1].base +
+				 type->regions[type->cnt - 1].size)
+		return type->cnt;
+
+	while (low < high) {
+		mid = (low + high) / 2;
+		if (type->regions[mid].base + type->regions[mid].size <= base)
+			low = mid + 1;
+		else
+			high = mid;
+	}
+	return low;
+}
+
 /**
  * memblock_add_range - add new memblock region
  * @type: memblock type to add new region into
@@ -651,7 +683,8 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
 	base = obase;
 	nr_new = 0;
 
-	for_each_memblock_type(idx, type, rgn) {
+	for_each_memblock_type_from(idx, type, rgn,
+				    memblock_bsearch_start(type, base)) {
 		phys_addr_t rbase = rgn->base;
 		phys_addr_t rend = rbase + rgn->size;
 
@@ -827,7 +860,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
 		if (memblock_double_array(type, base, size) < 0)
 			return -ENOMEM;
 
-	for_each_memblock_type(idx, type, rgn) {
+	for_each_memblock_type_from(idx, type, rgn,
+				    memblock_bsearch_start(type, base)) {
 		phys_addr_t rbase = rgn->base;
 		phys_addr_t rend = rbase + rgn->size;
 
-- 
2.55.0.970.g62bdec98f9-goog

Re: [PATCH] memblock: use binary search to locate candidate regions

[Dev Jain]

On 03/09/26 9:29 pm, Tarun Sahu wrote:
> Use binary search (memblock_bsearch_start) in memblock_add_range() and
> memblock_isolate_range() to locate candidate regions instead of linearly
> scanning from index 0.
> 
> Under heavy memory fragmentation (such as KHO page preservation registering
> hundreds of thousands of disjoint folios), scanning from index 0 on every
> insertion and isolation results in O(N^2) complexity, causing boot-time
> memory retrieval to take several minutes (~268s for 393k pages).
> 
> Using binary search reduces the worst-case complexity to O(N log N)
> (and O(N) for sequential appends), cutting KHO memory retrieval time
> from ~268s to ~50ms.
> 
> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
> ---

I recall noticing this 2 years ago : ) but then abandoned because
I couldn't think of a usecase.

I have forgotten memblock and no idea on KHO, but are you sure
this patch won't have negative consequence for the usual cases?
In other words is this something KHO specific, and in the usual
cases a linear search is more cache/CPU friendly?

Also below I see you have implemented a custom binary search helper.
I recall a generic one is there in some .h file somewhere in the
codebase, perhaps that may be useful, just FYI, ignore if already
tried that.

>  mm/memblock.c | 38 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 9ce86349a29f..88940474b020 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -160,6 +160,11 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>  	     i < memblock_type->cnt;					\
>  	     i++, rgn = &memblock_type->regions[i])
>  
> +#define for_each_memblock_type_from(i, memblock_type, rgn, start)	\
> +	for (i = (start), rgn = &memblock_type->regions[i];		\
> +	     i < memblock_type->cnt;					\
> +	     i++, rgn = &memblock_type->regions[i])
> +
>  #define memblock_dbg(fmt, ...)						\
>  	do {								\
>  		if (memblock_debug)					\
> @@ -591,6 +596,33 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
>  	type->total_size += size;
>  }
>  
> +/**
> + * memblock_bsearch_start - Find the first region index where rend > base
> + * @type: memblock type to search
> + * @base: base physical address of the candidate range
> + *
> + * Returns the first region index that could potentially overlap @base.
> + */
> +static int __init_memblock memblock_bsearch_start(struct memblock_type *type,
> +						  phys_addr_t base)
> +{
> +	int mid, low = 0;
> +	int high = type->cnt;
> +
> +	if (type->cnt && base >= type->regions[type->cnt - 1].base +
> +				 type->regions[type->cnt - 1].size)
> +		return type->cnt;
> +
> +	while (low < high) {
> +		mid = (low + high) / 2;
> +		if (type->regions[mid].base + type->regions[mid].size <= base)
> +			low = mid + 1;
> +		else
> +			high = mid;
> +	}
> +	return low;
> +}
> +
>  /**
>   * memblock_add_range - add new memblock region
>   * @type: memblock type to add new region into
> @@ -651,7 +683,8 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  	base = obase;
>  	nr_new = 0;
>  
> -	for_each_memblock_type(idx, type, rgn) {
> +	for_each_memblock_type_from(idx, type, rgn,
> +				    memblock_bsearch_start(type, base)) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  
> @@ -827,7 +860,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  		if (memblock_double_array(type, base, size) < 0)
>  			return -ENOMEM;
>  
> -	for_each_memblock_type(idx, type, rgn) {
> +	for_each_memblock_type_from(idx, type, rgn,
> +				    memblock_bsearch_start(type, base)) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  

Re: [PATCH] memblock: use binary search to locate candidate regions

[tarunsahu]

Dev Jain <dev.jain@arm.com> writes:

> On 03/09/26 9:29 pm, Tarun Sahu wrote:
>> Use binary search (memblock_bsearch_start) in memblock_add_range() and
>> memblock_isolate_range() to locate candidate regions instead of linearly
>> scanning from index 0.
>> 
>> Under heavy memory fragmentation (such as KHO page preservation registering
>> hundreds of thousands of disjoint folios), scanning from index 0 on every
>> insertion and isolation results in O(N^2) complexity, causing boot-time
>> memory retrieval to take several minutes (~268s for 393k pages).
>> 
>> Using binary search reduces the worst-case complexity to O(N log N)
>> (and O(N) for sequential appends), cutting KHO memory retrieval time
>> from ~268s to ~50ms.
>> 
>> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
>> ---
>
> I recall noticing this 2 years ago : ) but then abandoned because
> I couldn't think of a usecase.
>
> I have forgotten memblock and no idea on KHO, but are you sure
> this patch won't have negative consequence for the usual cases?
> In other words is this something KHO specific, and in the usual
> cases a linear search is more cache/CPU friendly?
>

Linear search on very large list: A very big problem
Linear search on small list (< 100): Good and almost 100% cache hit
because of next memory prediction by CPU.

Binary Search on very large list: very good thing
Binary search on small list (< 100): Algorithm anyway faster (worst case
cycle 3-4 vs 100 in linear search), yes cache miss is problem but IIUC,
To contribute to latency significantly, the quantity of such cache
misses is very less. Binary search uses more instruction per loop than
linear search, so of course linear search is better in this case, But
that micro/nano seconds latency affect is really an issue here? because
memblock is boot time initialization code. (Except memory hotplug) So No
userspace application like HFT or gaming will be affected by this.

So I believe, binary search wins here. Let me know your thoughts?

> Also below I see you have implemented a custom binary search helper.
> I recall a generic one is there in some .h file somewhere in the
> codebase, perhaps that may be useful, just FYI, ignore if already
> tried that.

This one does lower bound serach:  To find the first element where the
addition can be done instead of trying to find the exact match.

This one has a fast-path unlike to general binary search:

+	if (type->cnt && base >= type->regions[type->cnt - 1].base +
+				 type->regions[type->cnt - 1].size)
+		return type->cnt;

Also, I followed what memblock_search already does, Having its own
binary search.

~Tarun

>
>>  mm/memblock.c | 38 ++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 36 insertions(+), 2 deletions(-)
>> 
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 9ce86349a29f..88940474b020 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -160,6 +160,11 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>>  	     i < memblock_type->cnt;					\
>>  	     i++, rgn = &memblock_type->regions[i])
>>  
>> +#define for_each_memblock_type_from(i, memblock_type, rgn, start)	\
>> +	for (i = (start), rgn = &memblock_type->regions[i];		\
>> +	     i < memblock_type->cnt;					\
>> +	     i++, rgn = &memblock_type->regions[i])
>> +
>>  #define memblock_dbg(fmt, ...)						\
>>  	do {								\
>>  		if (memblock_debug)					\
>> @@ -591,6 +596,33 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
>>  	type->total_size += size;
>>  }
>>  
>> +/**
>> + * memblock_bsearch_start - Find the first region index where rend > base
>> + * @type: memblock type to search
>> + * @base: base physical address of the candidate range
>> + *
>> + * Returns the first region index that could potentially overlap @base.
>> + */
>> +static int __init_memblock memblock_bsearch_start(struct memblock_type *type,
>> +						  phys_addr_t base)
>> +{
>> +	int mid, low = 0;
>> +	int high = type->cnt;
>> +
>> +	if (type->cnt && base >= type->regions[type->cnt - 1].base +
>> +				 type->regions[type->cnt - 1].size)
>> +		return type->cnt;
>> +
>> +	while (low < high) {
>> +		mid = (low + high) / 2;
>> +		if (type->regions[mid].base + type->regions[mid].size <= base)
>> +			low = mid + 1;
>> +		else
>> +			high = mid;
>> +	}
>> +	return low;
>> +}
>> +
>>  /**
>>   * memblock_add_range - add new memblock region
>>   * @type: memblock type to add new region into
>> @@ -651,7 +683,8 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>>  	base = obase;
>>  	nr_new = 0;
>>  
>> -	for_each_memblock_type(idx, type, rgn) {
>> +	for_each_memblock_type_from(idx, type, rgn,
>> +				    memblock_bsearch_start(type, base)) {
>>  		phys_addr_t rbase = rgn->base;
>>  		phys_addr_t rend = rbase + rgn->size;
>>  
>> @@ -827,7 +860,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>>  		if (memblock_double_array(type, base, size) < 0)
>>  			return -ENOMEM;
>>  
>> -	for_each_memblock_type(idx, type, rgn) {
>> +	for_each_memblock_type_from(idx, type, rgn,
>> +				    memblock_bsearch_start(type, base)) {
>>  		phys_addr_t rbase = rgn->base;
>>  		phys_addr_t rend = rbase + rgn->size;
>>  

Re: [PATCH] memblock: use binary search to locate candidate regions

[Dongli Zhang]

On Thu, Sep 3, 2026 8:59:06AM -0700, Tarun Sahu wrote:
> Use binary search (memblock_bsearch_start) in memblock_add_range() and
> memblock_isolate_range() to locate candidate regions instead of linearly
> scanning from index 0.
> 
> Under heavy memory fragmentation (such as KHO page preservation registering
> hundreds of thousands of disjoint folios), scanning from index 0 on every
> insertion and isolation results in O(N^2) complexity, causing boot-time
> memory retrieval to take several minutes (~268s for 393k pages).
> 
> Using binary search reduces the worst-case complexity to O(N log N)
> (and O(N) for sequential appends), cutting KHO memory retrieval time
> from ~268s to ~50ms.

I encountered this issue with my workload. Initially, it was because I forgot to
set THP to "always", As a result, there were many 4K pages even though they were
contiguous.

Indeed, I noticed some delays or hiccups with my workload even with THP set to
"always".

In the past month, I used something like what I attached at the end of my reply
to reduce the number of memblock_reserve() calls. I never realized the poor
performance was caused by memblock_reserve() itself.

[    0.231623] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
--> delay
[   38.587378] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=32, Nodes=1

With your patch, I ran several rounds of tests with THP set to "never" (4K
pages) and no longer noticed any hiccups or delays with my workload.

[    0.247746] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
[    0.512019] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=32, Nodes=1


Thanks to this patch, I no longer have to put up with the delays or hiccups in
my workload!

Thank you very much!

Dongli Zhang


diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 7c4d86daf86d..03e1f914c800 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -67,6 +67,8 @@ union kho_page_info {
 static_assert(sizeof(union kho_page_info) == sizeof(((struct page *)0)->private));

 static bool kho_enable __ro_after_init =
IS_ENABLED(CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT);
+static phys_addr_t kho_preserved_batch_start __initdata;
+static phys_addr_t kho_preserved_batch_end __initdata;

 bool kho_is_enabled(void)
 {
@@ -610,25 +612,58 @@ static struct page *__init
kho_get_preserved_page(phys_addr_t phys,
 	return pfn_to_page(pfn);
 }

+static void __init kho_preserved_memory_batch_flush(void)
+{
+	phys_addr_t size;
+
+	if (kho_preserved_batch_start == kho_preserved_batch_end)
+		return;
+
+	size = kho_preserved_batch_end - kho_preserved_batch_start;
+	memblock_reserve(kho_preserved_batch_start, size);
+	memblock_reserved_mark_noinit(kho_preserved_batch_start, size);
+
+	kho_preserved_batch_start = 0;
+	kho_preserved_batch_end = 0;
+}
+
+static void __init kho_preserved_memory_batch_add(phys_addr_t phys,
+						  unsigned int order)
+{
+	phys_addr_t size = 1ULL << (order + PAGE_SHIFT);
+	phys_addr_t end = phys + size;
+
+	if (kho_preserved_batch_start == kho_preserved_batch_end) {
+		kho_preserved_batch_start = phys;
+		kho_preserved_batch_end = end;
+		return;
+	}
+
+	if (phys == kho_preserved_batch_end) {
+		kho_preserved_batch_end = end;
+		return;
+	}
+
+	kho_preserved_memory_batch_flush();
+	kho_preserved_batch_start = phys;
+	kho_preserved_batch_end = end;
+}
+
 static int __init kho_preserved_memory_reserve(unsigned long key, void *data)
 {
 	union kho_page_info info;
 	struct page *page;
 	unsigned int order;
 	phys_addr_t phys;
-	u64 sz;

 	phys = kho_decode_radix_key(key, &order);

-	sz = 1UL << (order + PAGE_SHIFT);
 	page = kho_get_preserved_page(phys, order);

-	/* Reserve the memory preserved in KHO in memblock */
-	memblock_reserve(phys, sz);
-	memblock_reserved_mark_noinit(phys, sz);
 	info.magic = KHO_PAGE_MAGIC;
 	info.order = order;
 	page->private = info.page_private;
+	kho_preserved_memory_batch_add(phys, order);

 	return 0;
 }
@@ -1687,8 +1722,13 @@ static void __init kho_mem_retrieve(void)
 		.leaf = kho_preserved_memory_reserve,
 	};

-	if (kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL))
+	kho_preserved_batch_start = 0;
+	kho_preserved_batch_end = 0;
+	if (kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL)) {
+		kho_preserved_memory_batch_flush();
 		goto err;
+	}
+	kho_preserved_memory_batch_flush();

 	return;

> 
> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
> ---
>  mm/memblock.c | 38 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 9ce86349a29f..88940474b020 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -160,6 +160,11 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>  	     i < memblock_type->cnt;					\
>  	     i++, rgn = &memblock_type->regions[i])
>  
> +#define for_each_memblock_type_from(i, memblock_type, rgn, start)	\
> +	for (i = (start), rgn = &memblock_type->regions[i];		\
> +	     i < memblock_type->cnt;					\
> +	     i++, rgn = &memblock_type->regions[i])
> +
>  #define memblock_dbg(fmt, ...)						\
>  	do {								\
>  		if (memblock_debug)					\
> @@ -591,6 +596,33 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
>  	type->total_size += size;
>  }
>  
> +/**
> + * memblock_bsearch_start - Find the first region index where rend > base
> + * @type: memblock type to search
> + * @base: base physical address of the candidate range
> + *
> + * Returns the first region index that could potentially overlap @base.
> + */
> +static int __init_memblock memblock_bsearch_start(struct memblock_type *type,
> +						  phys_addr_t base)
> +{
> +	int mid, low = 0;
> +	int high = type->cnt;
> +
> +	if (type->cnt && base >= type->regions[type->cnt - 1].base +
> +				 type->regions[type->cnt - 1].size)
> +		return type->cnt;
> +
> +	while (low < high) {
> +		mid = (low + high) / 2;
> +		if (type->regions[mid].base + type->regions[mid].size <= base)
> +			low = mid + 1;
> +		else
> +			high = mid;
> +	}
> +	return low;
> +}
> +
>  /**
>   * memblock_add_range - add new memblock region
>   * @type: memblock type to add new region into
> @@ -651,7 +683,8 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>  	base = obase;
>  	nr_new = 0;
>  
> -	for_each_memblock_type(idx, type, rgn) {
> +	for_each_memblock_type_from(idx, type, rgn,
> +				    memblock_bsearch_start(type, base)) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  
> @@ -827,7 +860,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  		if (memblock_double_array(type, base, size) < 0)
>  			return -ENOMEM;
>  
> -	for_each_memblock_type(idx, type, rgn) {
> +	for_each_memblock_type_from(idx, type, rgn,
> +				    memblock_bsearch_start(type, base)) {
>  		phys_addr_t rbase = rgn->base;
>  		phys_addr_t rend = rbase + rgn->size;
>  
> -- 
> 2.55.0.970.g62bdec98f9-goog
> 
> 

Re: [PATCH] memblock: use binary search to locate candidate regions

[tarunsahu]

Dongli Zhang <dongli.zhang@oracle.com> writes:

> On Thu, Sep 3, 2026 8:59:06AM -0700, Tarun Sahu wrote:
>> Use binary search (memblock_bsearch_start) in memblock_add_range() and
>> memblock_isolate_range() to locate candidate regions instead of linearly
>> scanning from index 0.
>> 
>> Under heavy memory fragmentation (such as KHO page preservation registering
>> hundreds of thousands of disjoint folios), scanning from index 0 on every
>> insertion and isolation results in O(N^2) complexity, causing boot-time
>> memory retrieval to take several minutes (~268s for 393k pages).
>> 
>> Using binary search reduces the worst-case complexity to O(N log N)
>> (and O(N) for sequential appends), cutting KHO memory retrieval time
>> from ~268s to ~50ms.
>
> I encountered this issue with my workload. Initially, it was because I forgot to
> set THP to "always", As a result, there were many 4K pages even though they were
> contiguous.
>
> Indeed, I noticed some delays or hiccups with my workload even with THP set to
> "always".
>
> In the past month, I used something like what I attached at the end of my reply
> to reduce the number of memblock_reserve() calls. I never realized the poor
> performance was caused by memblock_reserve() itself.
>
> [    0.231623] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
> --> delay
> [   38.587378] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=32, Nodes=1
>
> With your patch, I ran several rounds of tests with THP set to "never" (4K
> pages) and no longer noticed any hiccups or delays with my workload.
>
> [    0.247746] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
> [    0.512019] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=32, Nodes=1
>
>
> Thanks to this patch, I no longer have to put up with the delays or hiccups in
> my workload!
>
> Thank you very much!

Glad to know it helped and thanks for testing this.

>
> Dongli Zhang
>
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 7c4d86daf86d..03e1f914c800 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -67,6 +67,8 @@ union kho_page_info {
>  static_assert(sizeof(union kho_page_info) == sizeof(((struct page *)0)->private));
>
>  static bool kho_enable __ro_after_init =
> IS_ENABLED(CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT);
> +static phys_addr_t kho_preserved_batch_start __initdata;
> +static phys_addr_t kho_preserved_batch_end __initdata;
>
>  bool kho_is_enabled(void)
>  {
> @@ -610,25 +612,58 @@ static struct page *__init
> kho_get_preserved_page(phys_addr_t phys,
>  	return pfn_to_page(pfn);
>  }
>
> +static void __init kho_preserved_memory_batch_flush(void)
> +{
> +	phys_addr_t size;
> +
> +	if (kho_preserved_batch_start == kho_preserved_batch_end)
> +		return;
> +
> +	size = kho_preserved_batch_end - kho_preserved_batch_start;
> +	memblock_reserve(kho_preserved_batch_start, size);
> +	memblock_reserved_mark_noinit(kho_preserved_batch_start, size);
We can also combine these two function. IIUC, kho_preserved_batch_start
does not overlap with other reserved regions so, they will be mutually
exclusives ranges and can directly be marked noinit while adding to
reserved list.

~Tarun

> +
> +	kho_preserved_batch_start = 0;
> +	kho_preserved_batch_end = 0;
> +}
> +
> +static void __init kho_preserved_memory_batch_add(phys_addr_t phys,
> +						  unsigned int order)
> +{
> +	phys_addr_t size = 1ULL << (order + PAGE_SHIFT);
> +	phys_addr_t end = phys + size;
> +
> +	if (kho_preserved_batch_start == kho_preserved_batch_end) {
> +		kho_preserved_batch_start = phys;
> +		kho_preserved_batch_end = end;
> +		return;
> +	}
> +
> +	if (phys == kho_preserved_batch_end) {
> +		kho_preserved_batch_end = end;
> +		return;
> +	}
> +
> +	kho_preserved_memory_batch_flush();
> +	kho_preserved_batch_start = phys;
> +	kho_preserved_batch_end = end;
> +}
> +
>  static int __init kho_preserved_memory_reserve(unsigned long key, void *data)
>  {
>  	union kho_page_info info;
>  	struct page *page;
>  	unsigned int order;
>  	phys_addr_t phys;
> -	u64 sz;
>
>  	phys = kho_decode_radix_key(key, &order);
>
> -	sz = 1UL << (order + PAGE_SHIFT);
>  	page = kho_get_preserved_page(phys, order);
>
> -	/* Reserve the memory preserved in KHO in memblock */
> -	memblock_reserve(phys, sz);
> -	memblock_reserved_mark_noinit(phys, sz);
>  	info.magic = KHO_PAGE_MAGIC;
>  	info.order = order;
>  	page->private = info.page_private;
> +	kho_preserved_memory_batch_add(phys, order);
>
>  	return 0;
>  }
> @@ -1687,8 +1722,13 @@ static void __init kho_mem_retrieve(void)
>  		.leaf = kho_preserved_memory_reserve,
>  	};
>
> -	if (kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL))
> +	kho_preserved_batch_start = 0;
> +	kho_preserved_batch_end = 0;
> +	if (kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL)) {
> +		kho_preserved_memory_batch_flush();
>  		goto err;
> +	}
> +	kho_preserved_memory_batch_flush();
>
>  	return;
>
>> 
>> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
>> ---
>>  mm/memblock.c | 38 ++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 36 insertions(+), 2 deletions(-)
>> 
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 9ce86349a29f..88940474b020 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -160,6 +160,11 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>>  	     i < memblock_type->cnt;					\
>>  	     i++, rgn = &memblock_type->regions[i])
>>  
>> +#define for_each_memblock_type_from(i, memblock_type, rgn, start)	\
>> +	for (i = (start), rgn = &memblock_type->regions[i];		\
>> +	     i < memblock_type->cnt;					\
>> +	     i++, rgn = &memblock_type->regions[i])
>> +
>>  #define memblock_dbg(fmt, ...)						\
>>  	do {								\
>>  		if (memblock_debug)					\
>> @@ -591,6 +596,33 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
>>  	type->total_size += size;
>>  }
>>  
>> +/**
>> + * memblock_bsearch_start - Find the first region index where rend > base
>> + * @type: memblock type to search
>> + * @base: base physical address of the candidate range
>> + *
>> + * Returns the first region index that could potentially overlap @base.
>> + */
>> +static int __init_memblock memblock_bsearch_start(struct memblock_type *type,
>> +						  phys_addr_t base)
>> +{
>> +	int mid, low = 0;
>> +	int high = type->cnt;
>> +
>> +	if (type->cnt && base >= type->regions[type->cnt - 1].base +
>> +				 type->regions[type->cnt - 1].size)
>> +		return type->cnt;
>> +
>> +	while (low < high) {
>> +		mid = (low + high) / 2;
>> +		if (type->regions[mid].base + type->regions[mid].size <= base)
>> +			low = mid + 1;
>> +		else
>> +			high = mid;
>> +	}
>> +	return low;
>> +}
>> +
>>  /**
>>   * memblock_add_range - add new memblock region
>>   * @type: memblock type to add new region into
>> @@ -651,7 +683,8 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>>  	base = obase;
>>  	nr_new = 0;
>>  
>> -	for_each_memblock_type(idx, type, rgn) {
>> +	for_each_memblock_type_from(idx, type, rgn,
>> +				    memblock_bsearch_start(type, base)) {
>>  		phys_addr_t rbase = rgn->base;
>>  		phys_addr_t rend = rbase + rgn->size;
>>  
>> @@ -827,7 +860,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>>  		if (memblock_double_array(type, base, size) < 0)
>>  			return -ENOMEM;
>>  
>> -	for_each_memblock_type(idx, type, rgn) {
>> +	for_each_memblock_type_from(idx, type, rgn,
>> +				    memblock_bsearch_start(type, base)) {
>>  		phys_addr_t rbase = rgn->base;
>>  		phys_addr_t rend = rbase + rgn->size;
>>  
>> -- 
>> 2.55.0.970.g62bdec98f9-goog
>> 
>>