Re: [PATCH v3 7/8] ext4: Use rbtrees to manage PAs instead of inode i_prealloc_list

[Ojaswin Mujoo]

On Fri, Jan 27, 2023 at 03:43:12PM +0100, Jan Kara wrote:
> 
> Well, I think cond_resched() + goto retry would be OK here. We could also
> cycle the corresponding group lock which would wait for
> ext4_mb_discard_group_preallocations() to finish but that is going to burn
> the CPU even more than the cond_resched() + retry as we'll be just spinning
> on the spinlock. Sleeping is IMHO not warranted as the whole
> ext4_mb_discard_group_preallocations() is running under a spinlock anyway
> so it should better be a very short sleep.
> 
> Or actually I have one more possible solution: What the adjusting function
> is doing that it looks up PA before and after ac->ac_o_ex.fe_logical and
> trims start & end to not overlap these PAs. So we could just lookup these
> two PAs (ignoring the deleted state) and then just iterate from these with
> rb_prev() & rb_next() until we find not-deleted ones. What do you think? 

Hey Jan, 

Just thought I'd update you, I'm trying this solution out, and it looks
good but I'm hitting a few bugs in the implementation. Will update here
once I have it working correctly.

Regards,
Ojaswin