From 7933ad3f669670ca5f5f13de2b5cb0f92b91abf5 Mon Sep 17 00:00:00 2001 From: Tarun Sahu Date: Thu, 8 Oct 2026 19:08:28 +0000 Subject: [PATCH] memblock: use binary search to locate candidate regions 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 Reviewed-by: Pratyush Yadav Link: https://patch.msgid.link/20261008190828.3221718-2-tarunsahu@google.com Signed-off-by: Mike Rapoport (Microsoft) --- mm/memblock.c | 43 ++++++++++++++++++++++++++++--------------- 1 file changed, 28 insertions(+), 15 deletions(-) diff --git a/mm/memblock.c b/mm/memblock.c index 5acd6718a148..8ce808673d30 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -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; }