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 8A3CBCA601D for ; Fri, 9 Oct 2026 17:00:43 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: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=ztyPoTsXQl2erL+nCDtIS3iAw5yK7s2FnhInIimetvY=; b=Rlnrzv9jApmDSTa+5MJ6bJM4bR CiLRtJAorBNKI0/tY4CsPAfgxmC2JPxsu45RCVBwVuHolUdQIPTol8pmCRGMcjQ7HDMTXgtYCgOOS SFAOFRRxPAbrL086UDZkyO3BA5qV3rWywOX4Qf7KNREZyluGFeFyFd1p/WqVh07fMd8nvKV253ucn 4KQ2pInEOEaDP/t7lLHcxhYYGQ/p8PlV4h9+3ML4QeGbluwH/28Ws+xulYaWqaJZ4bCEKfbFNPhO+ 4IcO/ie4gVCOirPlGjkEjmIbwUAY5kpB01ktSJCfBdN8lzFdmyfgihQdS4xX3swihQ1efVum+fndk +y3UvziA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xFDxZ-00000006kGG-3Bwe; Fri, 09 Oct 2026 17:00:41 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xFDxR-00000006kDf-0QJu for kexec@lists.infradead.org; Fri, 09 Oct 2026 17:00:37 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id D36F640801; Fri, 9 Oct 2026 17:00:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8111C1F000FF; Fri, 9 Oct 2026 17:00:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791565232; bh=ztyPoTsXQl2erL+nCDtIS3iAw5yK7s2FnhInIimetvY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=PPBVQNEjP1rpUk9athtUmv4P1WtB+86fpqSx6AnywR1TtsvYSJIFmJNxilRtHzu6e fgQGXdRphhqRFLklVel6bYh6mpHunUliifxVYCBs+HAUBYHYMjbeas8wPR7ZsqJ/3V 7eFLqmJrb3o9bIyTjWzS5gtRj6YMUZSvkE1FTp1cIJPG7/2eAxipl58T6kYTuHqYw2 2aBWnqsCTriH0YTTyg9I5ATGBuVPFuG24npRcRxXy98EkvFS1hFqVdgoAMTbL1XWu1 ovV5WYF1EZtOHQLIlkOfsX/4VWk9KildRnDpshHtld1h/Kh1TJND71W4Folv/iGj2x isfpdlTkTKlyQ== Date: Fri, 9 Oct 2026 19:00:26 +0200 From: Mike Rapoport To: Tarun Sahu Cc: dmatlack@google.com, Pasha Tatashin , Andrew Morton , Pratyush Yadav , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] memblock: use binary search to locate candidate regions Message-ID: References: <20261008190828.3221718-1-tarunsahu@google.com> <20261008190828.3221718-2-tarunsahu@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261008190828.3221718-2-tarunsahu@google.com> 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 Thu, Oct 08, 2026 at 07:08:28PM +0000, Tarun Sahu wrote: > Use binary search (memblock_bsearch_start) in memblock_add_range() and The function name is __memblock_search now and I think you can drop it altogether :) > memblock_isolate_range() to locate candidate regions instead of linearly > scanning from index 0. > > Under heavy memory fragmentation (such as KHO page preservation registering Comma instead of open parenthesis feels better to me. > 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 > --- > mm/memblock.c | 45 +++++++++++++++++++++++++++++++-------------- > 1 file changed, 31 insertions(+), 14 deletions(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index 59dda7d085f3..614d0a55dd70 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 > + * > + * Returns the first region index that could potentially overlap @base. Return: for proper kernel-doc format AFAIR > + */ > +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 > @@ -644,8 +667,9 @@ static int __init_memblock memblock_add_range(struct memblock_type *type, > */ > base = obase; > nr_new = 0; > + idx = __memblock_search(type, base); > > - for (idx = 0; idx < type->cnt; idx++) { > + for (; idx < type->cnt; idx++) { for (idx = __memblock_search(type, base); ... > struct memblock_region *rgn = &type->regions[idx]; > phys_addr_t rbase = rgn->base; > phys_addr_t rend = rbase + rgn->size; > @@ -821,7 +845,9 @@ 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++) { > + idx = __memblock_search(type, base); > + > + for (; idx < type->cnt; idx++) { Same here or even for (int idx = __memblock_search(type, base); ... > struct memblock_region *rgn = &type->regions[idx]; > phys_addr_t rbase = rgn->base; > phys_addr_t rend = rbase + rgn->size; > @@ -2062,19 +2088,10 @@ 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; > - > - do { > - unsigned int mid = (right + left) / 2; > + int idx = __memblock_search(type, addr); > > - 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; > } > > -- > 2.56.0.385.gd3acb90ef8-goog > -- Sincerely yours, Mike.