2010/4/4, tytso@xxxxxxx <tytso@xxxxxxx>:
> On Sun, Apr 04, 2010 at 09:26:26AM +0800, jing zhang wrote:
>> > That being said, I'm not convinced ext4_mb_generate_from_freelist() is
>> > (a) necessary, or (b) bug-free, either. The whole point of having
>> > extents in bb_free_root tree is that those extents aren't safe to be
>> > placed in the buddy bitmap. And ext4_mb_generate_from_freelist()
>> > isn't freeing the nodes from the rbtree. Fortunately it looks like
>> > ext4_mb_generate_from_freelist is only getting called when the buddy
>> > bitmap is being set up, so the rbtree should be empty during those
>> > times.
>> >
>> > I need to do some more investigation, but I think the function can be
>> > removed entirely.
>>
>> Do you mean that ext4_mb_generate_from_freelist() can be removed entirely?
>
> Maybe. I need to do more investigation to be sure. The code in
> mballoc is subtle, and in some places there is stuff which is vestigal
> or misnamed, but it means that I'm going to be very careful before
> changing things.
>
> It also means that if you submit patches, you need to be very clear
> what you think the surrounding code is doing, why you think it's
> wrong, and how your patch make things better. For example, this:
>
> The function, ext4_mb_discard_group_preallocations(), works alone as
> hard as possible without correct understanding its caller's good
> thinking.
>
> And now try to relieve it in simple way.
>
> is almost useless as a comment. It doesn't help me understand the
> code. "hard as possible"? Huh? "without correct understanding"?
> How can code, unless it's artificially intelligent, have
> understanding? And if you meant the original author had no
> understanding, how do you know that? "caller's good thinking"? Same
> question; the calling code doesn't think.
>
> This sort of explanation isn't helpful in understanding the patch.
>
> - Ted
>
Another good lesson, I got it.
Thanks
- zj
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