Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755965AbcLTQfp (ORCPT ); Tue, 20 Dec 2016 11:35:45 -0500 Received: from mail-pg0-f65.google.com ([74.125.83.65]:33950 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752273AbcLTQfn (ORCPT ); Tue, 20 Dec 2016 11:35:43 -0500 Date: Tue, 20 Dec 2016 16:35:40 +0000 From: Wei Yang To: Michal Hocko Cc: Wei Yang , trivial@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2 1/2] mm/memblock.c: trivial code refine in memblock_is_region_memory() Message-ID: <20161220163540.GA13224@vultr.guest> Reply-To: Wei Yang References: <1482072470-26151-1-git-send-email-richard.weiyang@gmail.com> <1482072470-26151-2-git-send-email-richard.weiyang@gmail.com> <20161219151514.GB5175@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161219151514.GB5175@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2847 Lines: 93 On Mon, Dec 19, 2016 at 04:15:14PM +0100, Michal Hocko wrote: >On Sun 18-12-16 14:47:49, Wei Yang wrote: >> The base address is already guaranteed to be in the region by >> memblock_search(). > Hi, Michal Nice to receive your comment. >First of all the way how the check is removed is the worst possible... >Apart from that it is really not clear to me why checking the base >is not needed. You are mentioning memblock_search but what about other >callers? adjust_range_page_size_mask e.g... > Hmm... the memblock_search() is called by memblock_is_region_memory(). Maybe I paste the whole function here would clarify the change. int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size) { int idx = memblock_search(&memblock.memory, base); phys_addr_t end = base + memblock_cap_size(base, &size); if (idx == -1) return 0; return memblock.memory.regions[idx].base <= base && (memblock.memory.regions[idx].base + memblock.memory.regions[idx].size) >= end; } So memblock_search() will search "base" in memblock.memory. If "base" is not in memblock.memory, idx would be -1. Then following code will not be executed. And if the following code is executed, it means idx is not -1 and memblock_search() has found the "base" in memblock.memory.regions[idx], which is ture for statement (memblock.memory.regions[idx].base <= base). >You also didn't mention what is the motivation of this change? What will >work better or why it makes sense in general? > The purpose is to improve the code by reduce an extra check. >Also this seems to be a general purpose function so it should better >be robust. > I think it is as robust as it was. >> This patch removes the check on base. >> >> Signed-off-by: Wei Yang > >Without a proper justification and with the horrible way how it is done >Nacked-by: Michal Hocko > Not sure I make it clear or I may miss something? >> --- >> mm/memblock.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memblock.c b/mm/memblock.c >> index 7608bc3..cd85303 100644 >> --- a/mm/memblock.c >> +++ b/mm/memblock.c >> @@ -1615,7 +1615,7 @@ int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size >> >> if (idx == -1) >> return 0; >> - return memblock.memory.regions[idx].base <= base && >> + return /* memblock.memory.regions[idx].base <= base && */ >> (memblock.memory.regions[idx].base + >> memblock.memory.regions[idx].size) >= end; >> } >> -- >> 2.5.0 >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@kvack.org. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: email@kvack.org > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me