From: Martin Pieuchot <mpi@grenadille.net>
Subject: Re: anon pool cache
To: tech@openbsd.org
Date: Mon, 14 Apr 2025 09:48:09 +0200

On 10/03/25(Mon) 20:04, Martin Pieuchot wrote:
> The mutex of the anon pool is one of the most contended global locks in
> UVM.  Diff below makes it use a pool cache on MP kernels.  Without this,
> running the upper part of the fault handler in parallel doesn't improve
> anything.  This change already gives a small boost on its own.
> 
> Note that on LP64 "struct vm_anon" needs to grow a little bit...
> 
> ok?

This also help single-threaded performances...  Anyone?

> Index: uvm/uvm_anon.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_anon.c,v
> diff -u -p -r1.62 uvm_anon.c
> --- uvm/uvm_anon.c	10 Mar 2025 14:13:58 -0000	1.62
> +++ uvm/uvm_anon.c	10 Mar 2025 18:45:51 -0000
> @@ -50,6 +50,14 @@ uvm_anon_init(void)
>  	pool_sethiwat(&uvm_anon_pool, uvmexp.free / 16);
>  }
>  
> +void
> +uvm_anon_init_percpu(void)
> +{
> +#ifdef MULTIPROCESSOR
> +	pool_cache_init(&uvm_anon_pool);
> +#endif
> +}
> +
>  /*
>   * uvm_analloc: allocate a new anon.
>   *
> Index: uvm/uvm_anon.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_anon.h,v
> diff -u -p -r1.22 uvm_anon.h
> --- uvm/uvm_anon.h	19 Jan 2021 13:21:36 -0000	1.22
> +++ uvm/uvm_anon.h	10 Mar 2025 18:46:25 -0000
> @@ -47,6 +47,10 @@ struct vm_anon {
>  	 * Drum swap slot # (if != 0) [if we hold an_page, PG_BUSY]
>  	 */
>  	int an_swslot;
> +
> +#if defined(MULTIPROCESSOR) && defined(__LP64__)
> +	long unused;			/* to match pool_cache_item's size */
> +#endif
>  };
>  
>  /*
> @@ -84,6 +88,7 @@ void		 uvm_anfree_list(struct vm_anon *,
>  void		 uvm_anon_release(struct vm_anon *);
>  void		 uvm_anwait(void);
>  void		 uvm_anon_init(void);
> +void		 uvm_anon_init_percpu(void);
>  void		 uvm_anon_dropswap(struct vm_anon *);
>  boolean_t	 uvm_anon_pagein(struct vm_amap *, struct vm_anon *);
>  
> Index: uvm/uvm_init.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_init.c,v
> diff -u -p -r1.42 uvm_init.c
> --- uvm/uvm_init.c	20 Mar 2021 10:24:21 -0000	1.42
> +++ uvm/uvm_init.c	10 Mar 2025 18:37:33 -0000
> @@ -194,4 +194,6 @@ void
>  uvm_init_percpu(void)
>  {
>  	uvmexp_counters = counters_alloc_ncpus(uvmexp_counters, exp_ncounters);
> +
> +	uvm_anon_init_percpu();
>  }
> 
>