From: Michal Hocko <mhocko@kernel.org>
To: Chen Gang <chengang@emindsoft.com.cn>
Cc: Minchan Kim <minchan@kernel.org>,
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 <gang.chen.5i5j@gmail.com>
Subject: Re: [PATCH] mm: migrate: Use bool instead of int for the return value of PageMovable
Date: Tue, 12 Jul 2016 09:48:41 +0200 [thread overview]
Message-ID: <20160712074841.GE14586@dhcp22.suse.cz> (raw)
In-Reply-To: <5783F7DE.9020203@emindsoft.com.cn>
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 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.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-07-12 7:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-09 15:55 [PATCH] mm: migrate: Use bool instead of int for the return value of PageMovable chengang
2016-07-11 0:26 ` Minchan Kim
2016-07-11 19:47 ` Chen Gang
2016-07-12 7:15 ` Vlastimil Babka
2016-07-12 16:42 ` Chen Gang
2016-07-12 7:48 ` Michal Hocko [this message]
2016-07-12 16:50 ` Chen Gang
2016-07-13 7:53 ` Michal Hocko
2016-07-17 0:51 ` Chen Gang
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