Re: [PATCH] block/psi: make PSI annotations of submit_bio only work for file pages

[Johannes Weiner <hannes@cmpxchg.org>]

On Tue, Mar 22, 2022 at 02:47:42AM +0000, CGEL wrote:
> On Mon, Mar 21, 2022 at 10:33:20AM -0400, Johannes Weiner wrote:
> > On Wed, Mar 16, 2022 at 06:39:28AM +0000, cgel.zte@gmail.com wrote:
> > > From: Yang Yang <yang.yang29@zte.com.cn>
> > > 
> > > psi tracks the time spent on submitting the IO of refaulting file pages
> > > and anonymous pages[1]. But after we tracks refaulting anonymous pages
> > > in swap_readpage[2][3], there is no need to track refaulting anonymous
> > > pages in submit_bio.
> > > 
> > > So this patch can reduce redundant calling of psi_memstall_enter. And
> > > make it easier to track refaulting file pages and anonymous pages
> > > separately.
> > 
> > I don't think this is an improvement.
> > 
> > psi_memstall_enter() will check current->in_memstall once, detect the
> > nested call, and bail. Your patch checks PageSwapBacked for every page
> > being added. It's more branches for less robust code.
> 
> We are also working for a new patch to classify different reasons cause
> psi_memstall_enter(): reclaim, thrashing, compact, etc. This will help
> user to tuning sysctl, for example, if user see high compact delay, he
> may try do adjust THP sysctl to reduce the compact delay.
> 
> To support that, we should distinguish what's the reason cause psi in
> submit_io(), this patch does the job.

Please submit these patches together then. On its own, this patch
isn't desirable.