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memblock: use binary search to locate candidate regions

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Use binary search 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 candidate search complexity to O(log N)
(from O(N)), cutting KHO memory retrieval time from ~268s to ~50ms.

memblock_search() open codes the same binary search, so reimplement it on
top of the new helper.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://patch.msgid.link/20261008190828.3221718-2-tarunsahu@google.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
This commit is contained in:
Tarun Sahu 2026-10-08 19:08:28 +00:00 committed by Mike Rapoport (Microsoft)
parent aedb8dde08
commit 7933ad3f66
1 changed files with 28 additions and 15 deletions
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43
mm/memblock.c
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@ -586,6 +586,29 @@ static void __init_memblock memblock_insert_region(struct memblock_type *type,
type->total_size += size;
}
/**
* __memblock_search - Find the first region index where rend > base
* @type: memblock type to search
* @base: base physical address of the candidate range
*
* Return: the first region index that could potentially overlap @base.
*/
static int __init_memblock __memblock_search(struct memblock_type *type,
phys_addr_t base)
{
int mid, low = 0;
int high = 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
@ -645,7 +668,7 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
base = obase;
nr_new = 0;
for (idx = 0; idx < type->cnt; idx++) {
for (idx = __memblock_search(type, base); idx < type->cnt; idx++) {
struct memblock_region *rgn = &type->regions[idx];
phys_addr_t rbase = rgn->base;
phys_addr_t rend = rbase + rgn->size;
@ -809,7 +832,6 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
int *start_rgn, int *end_rgn)
{
phys_addr_t end = base + memblock_cap_size(base, &size);
int idx;
*start_rgn = *end_rgn = 0;
@ -821,7 +843,7 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
if (memblock_double_array(type, base, size) < 0)
return -ENOMEM;
for (idx = 0; idx < type->cnt; idx++) {
for (int idx = __memblock_search(type, base); idx < type->cnt; idx++) {
struct memblock_region *rgn = &type->regions[idx];
phys_addr_t rbase = rgn->base;
phys_addr_t rend = rbase + rgn->size;
@ -2028,19 +2050,10 @@ void __init memblock_mem_limit_remove_map(phys_addr_t limit)
static int __init_memblock memblock_search(struct memblock_type *type, phys_addr_t addr)
{
unsigned int left = 0, right = type->cnt;
int idx = __memblock_search(type, addr);
do {
unsigned int mid = (right + left) / 2;
if (addr < type->regions[mid].base)
right = mid;
else if (addr >= (type->regions[mid].base +
type->regions[mid].size))
left = mid + 1;
else
return mid;
} while (left < right);
if (idx < type->cnt && addr >= type->regions[idx].base)
return idx;
return -1;
}