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

[Waiman Long]

On 1/10/22 03:05, 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.
> >
> > Signed-off-by: Tim Murray <timmurray@xxxxxxxxxx>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

We could certainly implement a down_read() variant (e.g. 
down_read_lowprio()) with its own slowpath function to do this within 
the rwsem code as long as there is a good use-case for this kind of 
functionality.

Cheers,
Longman