From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f70.google.com (mail-oi0-f70.google.com [209.85.218.70]) by kanga.kvack.org (Postfix) with ESMTP id 21B5B6B025F for ; Tue, 12 Jul 2016 12:36:30 -0400 (EDT) Received: by mail-oi0-f70.google.com with SMTP id w207so35413489oiw.1 for ; Tue, 12 Jul 2016 09:36:30 -0700 (PDT) Received: from out1134-233.mail.aliyun.com (out1134-233.mail.aliyun.com. [42.120.134.233]) by mx.google.com with ESMTP id n64si12500005itb.52.2016.07.12.09.36.27 for ; Tue, 12 Jul 2016 09:36:28 -0700 (PDT) Message-ID: <57851DFF.2010202@emindsoft.com.cn> Date: Wed, 13 Jul 2016 00:42:39 +0800 From: Chen Gang MIME-Version: 1.0 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> <3e4d01ff-3fad-457e-b015-e06c35f8f714@suse.cz> In-Reply-To: <3e4d01ff-3fad-457e-b015-e06c35f8f714@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , Minchan Kim Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, mhocko@suse.com, 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 On 7/12/16 15:15, Vlastimil Babka wrote: > On 07/11/2016 09:47 PM, 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. > > You mean "caching"? I don't see how this is better for caching. After the push/pop, the same branch is still there, so it's not eliminated (which would be indeed better). Somehow the original version just avoids the function prologue (push rbp, mov rsp, rbp) for the !__PageMovable(page) case. That's something I would expect e.g. if it was marked likely(), but here it's probably just accidental that the heuristics think it's likely in the "int" case and not "bool". So it's not a valid reason for prefering int over bool. The question is perhaps if it's indeed likely or unlikely and should be marked as such :) > Oh, sorry, after check the details, the result is a little complex (2 things are mixed together, and likely can be also considered): - One return statement instead of the 3 statements which will change the detail instructions (in fact, it has negative effect). - gcc 6.0 and redhat gcc 4.8 generate the different results. The related output are: - If use one return statement instead of the 3 statements with gcc 6.0, the result is my original outputs which we discussed before. - If still use 3 statements (only use true, false instead of 1, 0) with gcc 6.0, the 2 outputs are equal. - If still use 3 statements (only use true, false instead of 1, 0) with gcc 4.8, the 2 outputs are different, and obviously, the bool will be a little better (no "xor %ebx,%ebx"). - If use one return statement instead of the 3 statements with gcc 4.8, the result is a little bad than keeping 3 statements. - If we add likely(), can get the same result: bool is a little better (no "movzbl %al,%eax"). All together: - For return statement, merging multi-statement together is not a good idea, it will let compiler generates a little bad code. - For gcc 6.0, in our case, the outputs are the same (and both enable 'likely', too). - For gcc 4.8, in our case, 'bool' output is a little better than 'int' (after enable 'likely', also get the same result) The int output by gcc 4.8: 0000000000001150 : 1150: 48 8b 57 08 mov 0x8(%rdi),%rdx 1154: 55 push %rbp 1155: 48 89 e5 mov %rsp,%rbp 1158: 53 push %rbx 1159: 31 db xor %ebx,%ebx 115b: 83 e2 03 and $0x3,%edx 115e: 48 83 fa 02 cmp $0x2,%rdx 1162: 74 05 je 1169 <__SetPageMovable+0x1169> 1164: 89 d8 mov %ebx,%eax 1166: 5b pop %rbx 1167: 5d pop %rbp 1168: c3 retq 1169: e8 00 00 00 00 callq 116e <__SetPageMovable+0x116e> 116e: 48 85 c0 test %rax,%rax 1171: 74 f1 je 1164 <__SetPageMovable+0x1164> 1173: 48 8b 40 68 mov 0x68(%rax),%rax 1177: 48 85 c0 test %rax,%rax 117a: 74 e8 je 1164 <__SetPageMovable+0x1164> 117c: 31 db xor %ebx,%ebx 117e: 48 83 78 68 00 cmpq $0x0,0x68(%rax) 1183: 0f 95 c3 setne %bl 1186: 89 d8 mov %ebx,%eax 1188: 5b pop %rbx 1189: 5d pop %rbp 118a: c3 retq 118b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) The bool output by gcc 4.8: 0000000000001150 : 1150: 48 8b 57 08 mov 0x8(%rdi),%rdx 1154: 55 push %rbp 1155: 48 89 e5 mov %rsp,%rbp 1158: 53 push %rbx 1159: 31 db xor %ebx,%ebx 115b: 83 e2 03 and $0x3,%edx 115e: 48 83 fa 02 cmp $0x2,%rdx 1162: 74 05 je 1169 <__SetPageMovable+0x1169> 1164: 89 d8 mov %ebx,%eax 1166: 5b pop %rbx 1167: 5d pop %rbp 1168: c3 retq 1169: e8 00 00 00 00 callq 116e <__SetPageMovable+0x116e> 116e: 48 85 c0 test %rax,%rax 1171: 74 f1 je 1164 <__SetPageMovable+0x1164> 1173: 48 8b 40 68 mov 0x68(%rax),%rax 1177: 48 85 c0 test %rax,%rax 117a: 74 e8 je 1164 <__SetPageMovable+0x1164> 117c: 48 83 78 68 00 cmpq $0x0,0x68(%rax) 1181: 0f 95 c3 setne %bl 1184: 89 d8 mov %ebx,%eax 1186: 5b pop %rbx 1187: 5d pop %rbp 1188: c3 retq 1189: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) The int output by gcc 4.8 with likely(): 0000000000001150 : 1150: 48 8b 47 08 mov 0x8(%rdi),%rax 1154: 83 e0 03 and $0x3,%eax 1157: 48 83 f8 02 cmp $0x2,%rax 115b: 74 03 je 1160 <__SetPageMovable+0x1160> 115d: 31 c0 xor %eax,%eax 115f: c3 retq 1160: 55 push %rbp 1161: 48 89 e5 mov %rsp,%rbp 1164: e8 00 00 00 00 callq 1169 <__SetPageMovable+0x1169> 1169: 48 85 c0 test %rax,%rax 116c: 74 16 je 1184 <__SetPageMovable+0x1184> 116e: 48 8b 40 68 mov 0x68(%rax),%rax 1172: 48 85 c0 test %rax,%rax 1175: 74 0d je 1184 <__SetPageMovable+0x1184> 1177: 48 83 78 68 00 cmpq $0x0,0x68(%rax) 117c: 5d pop %rbp 117d: 0f 95 c0 setne %al 1180: 0f b6 c0 movzbl %al,%eax 1183: c3 retq 1184: 31 c0 xor %eax,%eax 1186: 5d pop %rbp 1187: c3 retq 1188: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) 118f: 00 The bool output by gcc 4.8 with likely(): 0000000000001150 : 1150: 48 8b 47 08 mov 0x8(%rdi),%rax 1154: 83 e0 03 and $0x3,%eax 1157: 48 83 f8 02 cmp $0x2,%rax 115b: 74 03 je 1160 <__SetPageMovable+0x1160> 115d: 31 c0 xor %eax,%eax 115f: c3 retq 1160: 55 push %rbp 1161: 48 89 e5 mov %rsp,%rbp 1164: e8 00 00 00 00 callq 1169 <__SetPageMovable+0x1169> 1169: 48 85 c0 test %rax,%rax 116c: 74 13 je 1181 <__SetPageMovable+0x1181> 116e: 48 8b 40 68 mov 0x68(%rax),%rax 1172: 48 85 c0 test %rax,%rax 1175: 74 0a je 1181 <__SetPageMovable+0x1181> 1177: 48 83 78 68 00 cmpq $0x0,0x68(%rax) 117c: 5d pop %rbp 117d: 0f 95 c0 setne %al 1180: c3 retq 1181: 31 c0 xor %eax,%eax 1183: 5d pop %rbp 1184: c3 retq 1185: 66 66 2e 0f 1f 84 00 data32 nopw %cs:0x0(%rax,%rax,1) 118c: 00 00 00 00 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 (e??a??) Managing Natural Environments is the Duty of Human Beings. -- 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