From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 25D0ECA5FCE for ; Sun, 4 Oct 2026 13:47:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: Message-ID:Date:References:In-Reply-To:Subject:Cc:To:From:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2Anbtm+pdahgrR9ZC/t4cu36UZjvdx8AEA18HRuyx4U=; b=mPPQfwUNSJ6c4qre1AhL7eQ+Wj CPbbfqVHB+HnagZbAf3yvre7Ac0aYUh7ciiex2hubhe4HuRSn45QEFLNAPgBqcj5yFhy+4uGa5onH 3FJ9zhFlutggegJ1vfGjZv7Qd2wv6t3DIdkZHFmsnNgf9x4eXSibTjWSBSsLDDrTWoTGxetSYzSpz Xd6logc7MGUMUqmDQUoisqEdiGXtv5T6dUpf4BGRc9nw38qlnQvYw8CIvSroBXjM8TvR4K6utQ+Go BKzO4XnlDtMrZGVfOGl0VFVPDkw2kbUaExqGf2dH/VYQO5v2qbwSv5at3/xufhadt+ZMUGHhY+PCl T0LFM4ww==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xDMYY-0000000Erwd-3z1T; Sun, 04 Oct 2026 13:47:10 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xDMYX-0000000ErwW-3RGi for kexec@lists.infradead.org; Sun, 04 Oct 2026 13:47:10 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 6A8AB436EF; Sun, 4 Oct 2026 13:47:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 915591F000FF; Sun, 4 Oct 2026 13:47:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791121629; bh=2Anbtm+pdahgrR9ZC/t4cu36UZjvdx8AEA18HRuyx4U=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=VxhHcyw17121mWewQWnFBlYu36WeLuxLz3s760/ygRpHOFWiW8bTFngobR3fAy91w F1s4OP2siQlEdbeom+A0c7ukrdAI2zTErw1X22qTFMh7SIi7eE7iw4loPqsHFBobAu 68ewnymwJZ6caC1aE7V/FpxHLPVuPSJLcVQZ+xWsuEMefzBeD9b5Hx+ibfJgVHy5Md dy/CqZy0oru33VHC2txLf1g9Wd5aS+/axHyLERZhV1qTikLOp6/f0mzSrNb8wT8VJc S1XnWjiYpj1LRD3+fhTfaWIqZWUtBCe2ufRB0UoVE0z+MQ5gRpnb0kaEAhyKicwLYl kvo/Uswz0DQbg== From: Pratyush Yadav To: Tarun Sahu Cc: Andrew Morton , Pasha Tatashin , dmatlack@google.com, Mike Rapoport , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, dev.jain@arm.com, Pratyush Yadav , linux-mm@kvack.org Subject: Re: [PATCH v3 2/2] memblock: use binary search to locate candidate regions In-Reply-To: <20260926092448.4090401-2-tarunsahu@google.com> (Tarun Sahu's message of "Sat, 26 Sep 2026 09:24:48 +0000") References: <20260926092448.4090401-1-tarunsahu@google.com> <20260926092448.4090401-2-tarunsahu@google.com> Date: Sun, 04 Oct 2026 15:47:05 +0200 Message-ID: <2vxz8q4dlgrq.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Sat, Sep 26 2026, 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. > > memblock_search() open codes the same binary search, so reimplement it on > top of the new helper. > > Signed-off-by: Tarun Sahu > > mm/memblock.c | 53 +++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 37 insertions(+), 16 deletions(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index 59dda7d085f3..87c71435c80c 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -586,6 +586,33 @@ 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; In some testing I did of this patch some time ago, I recall that this check didn't have much of a difference on performance. The binary search is the real optimization. Do you think this check is worth keeping? Other than this, I only have a couple minor nitpicks below. Regardless of these small comments, this patch LGTM so feel free to add Reviewed-by: Pratyush Yadav > + > + 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 > @@ -609,7 +636,7 @@ static int __init_memblock memblock_add_range(struct memblock_type *type, > bool insert = false; > phys_addr_t obase = base; > phys_addr_t end = base + memblock_cap_size(base, &size); > - int idx, nr_new, start_rgn = -1, end_rgn; > + int idx, start_idx, nr_new, start_rgn = -1, end_rgn; > > if (!size) > return 0; > @@ -644,8 +671,9 @@ static int __init_memblock memblock_add_range(struct memblock_type *type, > */ > base = obase; > nr_new = 0; > + start_idx = memblock_bsearch_start(type, base); > > - for (idx = 0; idx < type->cnt; idx++) { > + for (idx = start_idx; idx < type->cnt; idx++) { Nit: why have start_idx as a separate variable? Why not assign idx to the result of memblock_bsearch_start() directly? > struct memblock_region *rgn = &type->regions[idx]; > phys_addr_t rbase = rgn->base; > phys_addr_t rend = rbase + rgn->size; > @@ -809,7 +837,7 @@ 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; > + int idx, start_idx; > > *start_rgn = *end_rgn = 0; > > @@ -821,7 +849,9 @@ 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++) { > + start_idx = memblock_bsearch_start(type, base); > + > + for (idx = start_idx; idx < type->cnt; idx++) { Same here. > struct memblock_region *rgn = &type->regions[idx]; > phys_addr_t rbase = rgn->base; > phys_addr_t rend = rbase + rgn->size; > @@ -2062,19 +2092,10 @@ 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_bsearch_start(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; > } > > base-commit: 1f18d740165163910df64d3063e1ad31648bc5e0 -- Regards, Pratyush Yadav