Re: ext4 writeback performance issue in 6.12

[Jan Kara]

On Thu 09-10-25 18:21:53, Matt Fleming wrote:
> On Thu, Oct 09, 2025 at 02:29:07PM +0200, Jan Kara wrote:
> > 
> > OK, so even if we reduce the somewhat pointless CPU load in the allocator
> > you aren't going to see substantial increase in your writeback throughput.
> > Reducing the CPU load is obviously a worthy goal but I'm not sure if that's
> > your motivation or something else that I'm missing :).
>  
> I'm not following. If you reduce the time it takes to allocate blocks
> during writeback, why will that not improve writeback throughput?

Maybe I misunderstood what you wrote about your profiles but you wrote that
we were spending about 4% of CPU time in the block allocation code. Even if
we get that close to 0%, you'd still gain only 4%. Or am I misunderstanding
something?

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR