Re: [PATCH] fs/buffer.c: remove per-CPU buffer_head lookup cache

[Matthew Wilcox]

On Mon, Jun 26, 2023 at 03:04:53PM -0300, Marcelo Tosatti wrote:
> Upon closer investigation, it was found that in current codebase, lookup_bh_lru
> is slower than __find_get_block_slow:
> 
>  114 ns per __find_get_block
>  68 ns per __find_get_block_slow
> 
> So remove the per-CPU buffer_head caching.

LOL.  That's amazing.  I can't even see why it's so expensive.  The
local_irq_disable(), perhaps?  Your test case is the best possible
one for lookup_bh_lru() where you're not even doing the copy.

Reviewed-by: Matthew Wilcox (oracle) <willy@xxxxxxxxxxxxx>