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Date: Tue, 12 Jul 2016 03:47:42 +0800
From: Chen Gang <chengang@...ndsoft.com.cn>
To: Minchan Kim <minchan@...nel.org>
CC: akpm@...ux-foundation.org, vbabka@...e.cz,
mgorman@...hsingularity.net, mhocko@...e.com,
gi-oh.kim@...fitbricks.com, iamjoonsoo.kim@....com,
hillf.zj@...baba-inc.com, rientjes@...gle.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Chen Gang <gang.chen.5i5j@...il.com>
Subject: Re: [PATCH] mm: migrate: Use bool instead of int for the return value
of PageMovable
On 7/11/16 08:26, Minchan Kim wrote:
> On Sat, Jul 09, 2016 at 11:55:04PM +0800, chengang@...ndsoft.com.cn wrote:
>> From: Chen Gang <chengang@...ndsoft.com.cn>
>>
>> For pure bool function's return value, bool is a little better more or
>> less than int.
>>
>> And return boolean result directly, since 'if' statement is also for
>> boolean checking, and return boolean result, too.
>
> I just wanted to consistent with other PageXXX flags functions, PageAnon,
> PageMappingFlags which returns int rather than bool. Although I agree bool
> is natural, I want to be consistent with others rather than breaking at
> the moment.
>
> Maybe if you feel it's really helpful, you might be able to handle all
> of places I mentioned for better readability and keeping consistency.
OK, I guess, we can send another patch for include/linux/page-flags.h
for PageXXX.
> But I doubt it's worth.
>
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 orig:
0000000000001290 <PageMovable>:
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 <PageMovable>:
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.
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