Re: [PATCH] mm/page_alloc: replace local_lock with normal spinlock -fix -fix

From: Mel Gorman
Date: Fri Jul 08 2022 - 11:58:47 EST

On Fri, Jul 08, 2022 at 04:54:47PM +0200, Vlastimil Babka wrote:
> On 7/8/22 16:44, Mel Gorman wrote:
> > pcpu_spin_unlock and pcpu_spin_unlock_irqrestore both unlock
> > pcp->lock and then enable preemption. This lacks symmetry against
> > both the pcpu_spin helpers and differs from how local_unlock_* is
> > implemented. While this is harmless, it's unnecessary and it's generally
> > better to unwind locks and preemption state in the reverse order as
> > they were acquired.
> Hm I'm confused, it seems it's done in reverse order (which I agree with)
> before this -fix-fix, but not after it?
> before, pcpu_spin_lock() (and variants) do pcpu_task_pin() and then
> spin_lock() (or variant), and pcpu_spin_unlock() does spin_unlock() and then
> pcpu_task_unpin(). That seems symmetrical, i.e. reverse order to me? And
> seems to match what local_lock family does too.

You're not confused, I am. The patch and the changelog are outright brain
damage from excessive context switching and a sign that it's time for the
weekend to start.

Sorry for this absolute misfortune.

Mel Gorman