Re: [PATCH] btrfs: make btrfs_node_key static inline

[Su Yue <l@damenly.su>]

On Tue 14 Sep 2021 at 16:36, David Sterba <dsterba@suse.cz> wrote:

> On Tue, Sep 14, 2021 at 10:08:36PM +0800, Su Yue wrote:
>>
>> On Tue 14 Sep 2021 at 15:12, David Sterba <dsterba@suse.cz> 
>> wrote:
>>
>> > On Tue, Sep 14, 2021 at 06:53:35PM +0800, Su Yue wrote:
>> >> It looks strange that btrfs_node_key is in struct-funcs.c.
>> >> So move it to ctree.h and make it static inline.
>> >
>> > "looks strange" is not a sufficient reason. Inlining a 
>> > function
>> > means
>> > that the body will be expanded at each call site, bloating 
>> > the
>> > binary
>> > code. Have you measured the impact of that?
>> >
>> Fair enough.
>>
>> Before:
>>    text    data     bss     dec     hex filename
>> 1202418  123105   19384 1344907  14858b fs/btrfs/btrfs.ko
>> After:
>>    text    data     bss     dec     hex filename
>> 1202620  123105   19384 1345109  148655 fs/btrfs/btrfs.ko
>>
>> +202
>>
>> > There's some performance cost of an non-inline function due 
>> > to
>> > the call
>> > overhead but it does not make sense to inline a function 
>> > that's
>> > called
>> > rarely and not in a tight loop. If you grep for the function
>> > you'd see
>> > that it's called eg. once per function or in a loop that's 
>> > not
>> > performance critical on first sight (eg. in 
>> > reada_for_search).
>>
>> Right, the patch won't impact performance obviously at the cost 
>> of
>> +202 binary size. So I'd drop the patch.
>
> It does increase the size a bit but from what I've seen in the 
> assembly
> it's not that bad and still probably worth doing the inline. 
> There's one
> more extra call to read_extent_buffer (hidden behind 
> read_eb_member
> macro).
>
Thanks for taking a look. I just noticed the lonely function then 
post
the patch without deeper thinking.

> Cleaning up the node key helpers would be useful too, adding 
> some
> more helpers and not calling read_eb_member in the end. I have a 
> WIP
> patchset for that but had to leave it as there were bugs I did 
> not find.
> I can bounce it to you if you're interested.

Thanks a lot. But I can't take it due to some reasons. Since you 
have
a better WIP patchset, I don't mind forgoing the patch.

--
Su