From: Martin Pieuchot <mpi@grenadille.net>
Subject: Re: uvm_fault: loaned pages leftovers
To: tech@openbsd.org
Date: Mon, 20 Jan 2025 10:09:24 +0100

On 03/01/25(Fri) 16:39, Martin Pieuchot wrote:
> OpenBSD's UVM doesn't have support for loaned pages.  Diff below removes
> dead code related to such pages.
> 
> I've been hitting this hard on my 24 CPUs amd64.  ok?

Anyone?

> Index: uvm/uvm_fault.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_fault.c,v
> diff -u -p -r1.158 uvm_fault.c
> --- uvm/uvm_fault.c	27 Dec 2024 12:04:40 -0000	1.158
> +++ uvm/uvm_fault.c	1 Jan 2025 15:31:38 -0000
> @@ -321,16 +321,9 @@ uvmfault_anonget(struct uvm_faultinfo *u
>  			 * The last unlock must be an atomic unlock and wait
>  			 * on the owner of page.
>  			 */
> -			if (pg->uobject) {
> -				/* Owner of page is UVM object. */
> -				uvmfault_unlockall(ufi, amap, NULL);
> -				uvm_pagewait(pg, pg->uobject->vmobjlock,
> -				    "anonget1");
> -			} else {
> -				/* Owner of page is anon. */
> -				uvmfault_unlockall(ufi, NULL, NULL);
> -				uvm_pagewait(pg, anon->an_lock, "anonget2");
> -			}
> +			KASSERT(pg->uobject == NULL);
> +			uvmfault_unlockall(ufi, NULL, NULL);
> +			uvm_pagewait(pg, anon->an_lock, "anonget");
>  		} else {
>  			/*
>  			 * No page, therefore allocate one.
> @@ -998,8 +997,6 @@ uvm_fault_upper(struct uvm_faultinfo *uf
>  	 * if it fails (!OK) it will unlock everything for us.
>  	 * if it succeeds, locks are still valid and locked.
>  	 * also, if it is OK, then the anon's page is on the queues.
> -	 * if the page is on loan from a uvm_object, then anonget will
> -	 * lock that object for us if it does not fail.
>  	 */
>  	error = uvmfault_anonget(ufi, amap, anon);
>  	switch (error) {
> 
>