Re: [PATCH] f2fs: move f2fs to use reader-unfair rwsems

[Peter Zijlstra]

On Mon, Jan 10, 2022 at 12:05:26AM -0800, Christoph Hellwig wrote:
> Adding the locking primitive maintainers to this patch adding open coded
> locking primitives..
> 
> On Sat, Jan 08, 2022 at 08:46:17AM -0800, Jaegeuk Kim wrote:
> > From: Tim Murray <timmurray@xxxxxxxxxx>
> > 
> > f2fs rw_semaphores work better if writers can starve readers,
> > especially for the checkpoint thread, because writers are strictly
> > more important than reader threads. This prevents significant priority
> > inversion between low-priority readers that blocked while trying to
> > acquire the read lock and a second acquisition of the write lock that
> > might be blocking high priority work.

*groan*... that's nowhere near enough Changelog to justify any of this.
Because next is a whole series of patches making things even worse
because lockdep no longers works as expected on this custom thing.

Can we start by describing the actual problem?