From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 077D43E0234 for ; Sun, 6 Sep 2026 10:25:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788690335; cv=none; b=lrNEIi10vHKHNgTGUZHuSJXg/1CHGj66Enw4nJ2moaKNP3Xr5WE1zDmphQ3xXlCGQm3C4MfSbJuiisQP0sexIH74jTkvaCfWqy4LgOvbUlm2cIjR6024gG8rXCu+tG1WbWuBPZFteUAawu0gIsVOZJ9qcUm3MfzKwvionVrT0wU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788690335; c=relaxed/simple; bh=f/K93XfnCe4oB5F0XkA4i4OrBScfOrs8uaKROs6hPOI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lZ9ukHwjnv+vH8GBI7Qd1f1nkQEDSW0hUYyj0QV1aDQNSVOjJJz5+phcsnquFQb/x1CNc2/0miOxzJxR0mIv6DRbV02pWTo17pzxCddp+zzQwlJnwUID9epgtUGevARCmBt0ooHjkhxpl7s7RleP6stBMw+TnCbuJactKUggsY0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aT+A71hJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="aT+A71hJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7C4E71F00A3A; Sun, 6 Sep 2026 10:25:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788690332; bh=2XPq6jBsWxzSGkLN5JMNAqBj9VumCx6phCWWl2LqB4Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=aT+A71hJ8NCIRzwZvUAlmCF2acDHq2xysOzGVgGT3iPsEhswJ4mdi3jeaJj0iN+1f HJ8Wr8RRz4il12phVpTJYqK7TZm6HBoFHc23BkPlzoVI5sOLzIcKxRJuafbti3zxqq bBXfVWqy+KEdv6XsvE4Qy0digyusQeELvEYWRpU8teA74oWoYP3Zt0fHRT4wrmKt5g 0m94g72F2kB5Tbe47F6EGnNZHQc88m1JsxF1TNvzE9iMJY45iWStpPyPTxmO6fgjcY wZ3IdvyxptArEnj1FQAsXDPHZTNWBFUPdAkGExdGbWnfmejDhiw5BQZPl6GBlhefSg 0tHqpXaRiaZLg== Date: Sun, 6 Sep 2026 13:25:25 +0300 From: Mike Rapoport To: Tarun Sahu Cc: dmatlack@google.com, Pasha Tatashin , Andrew Morton , Pratyush Yadav , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] memblock: use binary search to locate candidate regions Message-ID: References: <20260903155907.1065681-1-tarunsahu@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260903155907.1065681-1-tarunsahu@google.com> Hi Tarun, On Thu, Sep 03, 2026 at 03:59:06PM +0000, 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 > --- > 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) > +{ We already have memblock_search() ;-) > + 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)) { I think we can just kill for_each_memblock_type() and open code all loops that use it and make memblock_add_range() and memblock_isolate_range() use binary search. > 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 > -- Sincerely yours, Mike.