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 2585038E5C8 for ; Sat, 3 Oct 2026 07:56:12 +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=1791014174; cv=none; b=jPaouMC1aZ0BTGFpx6sJ9CFHCEgn4xZ8dH/4ghe7+Im32sxQK4ZslSvrClW0jOGzubWzhXayMHQMzbuGef+brnTGbWlkiYPKVlzUN85kvQKaewckOuCBIi9oToX93J4VrVz1fcecSaKkjX4B0CpAVC0N/EJPsM+Ir5FYFbWB9+4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791014174; c=relaxed/simple; bh=k0J6W1MsAzAFB4BTPOdrFa7JvTaIBlAmVwyzoKYbEK4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gpkWX+N8th4dWrlkJxD5XIjN+B7GviHopMXM53+3QyBEjmvqTGAQAvRG96I9sXYpSyKNcZZFKlH/uZSB0CkyJ9nRtRF85pVawVNXWGnyc9AljiYbO6Nbeii1LjlLSCifN7i2UMxAdvlw6YzVJH8cys0tp1QQh5pGIWV+AkLEqB0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VRLJc7Hy; 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="VRLJc7Hy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67E6A1F0089B; Sat, 3 Oct 2026 07:56:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791014172; bh=UPO4RM0i7SP/IETP8H+05lmtRukMrZzOkuL7g4aF8U4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=VRLJc7HyEynjBACssz2mmFo30gjCyNt5Q471QjoAwHeXP5o4nCvfFp9iyqR2qwIYy rdqKYt47RndMm6y1XcQ1FG8JEyO/28b1E10zVwA4k4cSfHfXz9a3q0FS4/ISdbLKOC 75jgXrEMNeuWwhSa8lOgEgKFM1e1ytwEe/cQK0NnbQgVRgoSaIE+nx/ug084XIddZN yOIMS7FjC7SBakdQIeX3JIw7XCAE8j2vFG8jjmOCrjuhh2/LjnWS55aGmORTvWuvbJ HE7kIH1M+QqWOfDYzLHCKurMsqEw4mKRNR1LmeCrzdw0+Lxe3xXPkdJgRE0FZ79p/q JgL18ukxU0ciQ== Date: Sat, 3 Oct 2026 09:56:07 +0200 From: Mike Rapoport To: Tarun Sahu Cc: Andrew Morton , Pasha Tatashin , dmatlack@google.com, 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 Message-ID: References: <20260926092448.4090401-1-tarunsahu@google.com> <20260926092448.4090401-2-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: <20260926092448.4090401-2-tarunsahu@google.com> On Sat, Sep 26, 2026 at 09:24:48AM +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. > > 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) I'd call it __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; Using local variables would make it more readable IMHO. > + > + 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++) { > 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++) { > 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 > -- > 2.56.0.rc1.315.gc6ed9934b7-goog > -- Sincerely yours, Mike.