Re: [PATCH v2] fs: cache the string generated by reading /proc/filesystems

[Christian Brauner]

 On Wed, Apr 22, 2026 at 08:17:11PM +0200, Mateusz Guzik wrote:
> It is being read surprisingly often (e.g., by mkdir, ls and even sed!).
> 
> This is lock-protected pointer chasing over a linked list to pay for
> sprintf for every fs (32 on my boxen).
> 
> Instead cache the result.
> 
> open+read+close cycle single-threaded (ops/s):
> before:	442732
> after:	1063462 (+140%)
> 
> Here the main bottleneck is memcg.
> 
> Scalability-wise problems are avoidable lockref trip on open and ref
> management for the file on procfs side.
> 
> The file looks like a sterotypical C from the 90s, right down to an
> open-coded and slightly obfuscated linked list. I intentionally did not
> clean up any of it -- I think the file will be best served by a Rust
> rewrite when the time comes.
> 
> Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx>
> ---

Ugh, can't we at least also get rid of the rwlock stuff?
Something like the appended two (completely untested) patches.