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

From: Matthew Wilcox
Date: Mon Jun 26 2023 - 14:47:49 EST


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>