From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755511AbcGLQtk (ORCPT ); Tue, 12 Jul 2016 12:49:40 -0400 Received: from out1134-185.mail.aliyun.com ([42.120.134.185]:46448 "EHLO out1134-185.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754854AbcGLQth (ORCPT ); Tue, 12 Jul 2016 12:49:37 -0400 X-Greylist: delayed 316 seconds by postgrey-1.27 at vger.kernel.org; Tue, 12 Jul 2016 12:49:36 EDT X-Alimail-AntiSpam: AC=CONTINUE;BC=0.07453775|-1;FP=0|0|0|0|0|-1|-1|-1;HT=e01l10437;MF=chengang@emindsoft.com.cn;NM=1;PH=DS;RN=12;RT=12;SR=0;TI=SMTPD_----50YIBtz_1468341833; Message-ID: <57851FC4.4000000@emindsoft.com.cn> Date: Wed, 13 Jul 2016 00:50:12 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Michal Hocko CC: Minchan Kim , akpm@linux-foundation.org, vbabka@suse.cz, mgorman@techsingularity.net, gi-oh.kim@profitbricks.com, iamjoonsoo.kim@lge.com, hillf.zj@alibaba-inc.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chen Gang Subject: Re: [PATCH] mm: migrate: Use bool instead of int for the return value of PageMovable References: <1468079704-5477-1-git-send-email-chengang@emindsoft.com.cn> <20160711002605.GD31817@bbox> <5783F7DE.9020203@emindsoft.com.cn> <20160712074841.GE14586@dhcp22.suse.cz> In-Reply-To: <20160712074841.GE14586@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/12/16 15:48, Michal Hocko wrote: > On Tue 12-07-16 03:47:42, Chen Gang wrote: > [...] >> In our case, the 2 output size are same, but under x86_64, the insns are >> different. After uses bool, it uses push/pop instead of branch, for me, >> it should be a little better for catching. > > The code generated for bool version looks much worse. Look at the fast > path. Gcc tries to reuse the retq from the fast path in the bool case > and so it has to push rbp and rbx on the stack. > > That being said, gcc doesn't seem to generate a better code for bool so > I do not think this is really worth it. > The code below also merge 3 statements into 1 return statement, although for me, it is a little more readable, it will generate a little bad code. That is the reason why the output looks a little bad. In our case, for gcc 6.0, using bool instead of int for bool function will get the same output under x86_64. In our case, for gcc 4.8, using bool instead of int for bool function will get a little better output under x86_64. Thanks. >> The orig: >> >> 0000000000001290 : >> 1290: 48 8b 47 08 mov 0x8(%rdi),%rax >> 1294: 83 e0 03 and $0x3,%eax >> 1297: 48 83 f8 02 cmp $0x2,%rax >> 129b: 74 03 je 12a0 <__SetPageMovable+0x12a0> >> 129d: 31 c0 xor %eax,%eax >> 129f: c3 retq >> 12a0: 55 push %rbp >> 12a1: 48 89 e5 mov %rsp,%rbp >> 12a4: e8 00 00 00 00 callq 12a9 <__SetPageMovable+0x12a9> >> 12a9: 48 85 c0 test %rax,%rax >> 12ac: 74 17 je 12c5 <__SetPageMovable+0x12c5> >> 12ae: 48 8b 50 68 mov 0x68(%rax),%rdx >> 12b2: 48 85 d2 test %rdx,%rdx >> 12b5: 74 0e je 12c5 <__SetPageMovable+0x12c5> >> 12b7: 48 83 7a 68 00 cmpq $0x0,0x68(%rdx) >> 12bc: b8 01 00 00 00 mov $0x1,%eax >> 12c1: 74 02 je 12c5 <__SetPageMovable+0x12c5> >> 12c3: 5d pop %rbp >> 12c4: c3 retq >> 12c5: 31 c0 xor %eax,%eax >> 12c7: 5d pop %rbp >> 12c8: c3 retq >> 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) >> >> The new: >> >> 0000000000001290 : >> 1290: 48 8b 47 08 mov 0x8(%rdi),%rax >> 1294: 55 push %rbp >> 1295: 48 89 e5 mov %rsp,%rbp >> 1298: 53 push %rbx >> 1299: 31 db xor %ebx,%ebx >> 129b: 83 e0 03 and $0x3,%eax >> 129e: 48 83 f8 02 cmp $0x2,%rax >> 12a2: 74 05 je 12a9 <__SetPageMovable+0x12a9> >> 12a4: 89 d8 mov %ebx,%eax >> 12a6: 5b pop %rbx >> 12a7: 5d pop %rbp >> 12a8: c3 retq >> 12a9: e8 00 00 00 00 callq 12ae <__SetPageMovable+0x12ae> >> 12ae: 48 85 c0 test %rax,%rax >> 12b1: 74 f1 je 12a4 <__SetPageMovable+0x12a4> >> 12b3: 48 8b 40 68 mov 0x68(%rax),%rax >> 12b7: 48 85 c0 test %rax,%rax >> 12ba: 74 e8 je 12a4 <__SetPageMovable+0x12a4> >> 12bc: 48 83 78 68 00 cmpq $0x0,0x68(%rax) >> 12c1: 0f 95 c3 setne %bl >> 12c4: 89 d8 mov %ebx,%eax >> 12c6: 5b pop %rbx >> 12c7: 5d pop %rbp >> 12c8: c3 retq >> 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) >> >> Thanks. >> -- >> Chen Gang (陈刚) >> >> Managing Natural Environments is the Duty of Human Beings. > -- Chen Gang (陈刚) Managing Natural Environments is the Duty of Human Beings.