From: Wei Yang <richard.weiyang@gmail.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Wei Yang <richard.weiyang@gmail.com>,
linux-mm@kvack.org, akpm@linux-foundation.org
Subject: Re: [PATCH] mm, page_alloc: cleanup usemap_size() when SPARSEMEM is not set
Date: Fri, 25 Jan 2019 01:12:25 +0000 [thread overview]
Message-ID: <20190125011225.2vtcjtt64wrv36di@master> (raw)
In-Reply-To: <20190124143008.GO4087@dhcp22.suse.cz>
On Thu, Jan 24, 2019 at 03:30:08PM +0100, Michal Hocko wrote:
>On Thu 24-01-19 14:13:41, Wei Yang wrote:
>> On Wed, Jan 23, 2019 at 10:55:03AM +0100, Michal Hocko wrote:
>> >On Tue 22-01-19 15:56:28, Wei Yang wrote:
>> >>
>> >> I think the answer is yes.
>> >>
>> >> * it reduce the code from 6 lines to 3 lines, 50% off
>> >> * by reducing calculation back and forth, it would be easier for
>> >> audience to catch what it tries to do
>> >
>> >To be honest, I really do not see this sufficient to justify touching
>> >the code unless the resulting _generated_ code is better/more efficient.
>>
>> Tried objdump to compare two version.
>>
>> Base Patched Reduced
>> Code Size(B) 48 39 18.7%
>> Instructions 12 10 16.6%
>
>How have you compiled the code? (compiler version, any specific configs).
>Because I do not see any difference.
Yes, of course I have hacked and compiled the code.
I guess you compile the code on x86, which by default SPARSEMEM is
configured. This means those changes are not compiled.
To get the result, I have hacked the code to add the definition to
mm/sparse.c and call this new function to make sure compile will not
optimize this out.
Below is the result from readelf -S mm/sparse.o
>
>CONFIG_CC_OPTIMIZE_FOR_SIZE:
> text data bss dec hex filename
> 47087 2085 72 49244 c05c mm/page_alloc.o
> 47087 2085 72 49244 c05c mm/page_alloc.o.prev
text: 0x2c7 -> 0x2be reduced 9 bytes
>
>CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE:
> text data bss dec hex filename
> 55046 2085 72 57203 df73 mm/page_alloc.o
> 55046 2085 72 57203 df73 mm/page_alloc.o.prev
text: 0x35b -> 0x34b reduced 16 bytes
>
>And that would actually match my expectations because I am pretty sure
>the compiler can figure out what to do with those operations even
>without any help.
>
>Really, is this really worth touching and spending a non-trivial time to
>discuss? I do not see the benefit.
I thought this is a trivial change and we have the same taste of the
code.
I agree to put an end to this thread.
Thanks for your time.
>--
>Michal Hocko
>SUSE Labs
--
Wei Yang
Help you, Help me
prev parent reply other threads:[~2019-01-25 1:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-18 23:49 [PATCH] mm, page_alloc: cleanup usemap_size() when SPARSEMEM is not set Wei Yang
2019-01-22 8:55 ` Michal Hocko
2019-01-22 15:07 ` Wei Yang
2019-01-22 15:16 ` Michal Hocko
2019-01-22 15:56 ` Wei Yang
2019-01-23 9:55 ` Michal Hocko
2019-01-24 14:13 ` Wei Yang
2019-01-24 14:30 ` Michal Hocko
2019-01-25 1:12 ` Wei Yang [this message]
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