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
