From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: Document vm_page locking
To: Martin Pieuchot <mpi@grenadille.net>
Cc: tech@openbsd.org
Date: Mon, 17 Feb 2025 19:40:40 +0100

> Date: Mon, 17 Feb 2025 16:45:48 +0100
> From: Martin Pieuchot <mpi@grenadille.net>
> 
> Diff below documents which fields from `vm_page' are protected by which
> lock/mechanism.
> 
> I left out fields used by pmaps and `pg_version' which is only for debug
> purpose and not needed for what I need to achieve: reduce the contention
> on the `pageqlock'.
> 
> ok?

Why are you changing some of the types from u_int -> uint32_t?

> Index: uvm/uvm_page.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_page.h,v
> diff -u -p -r1.71 uvm_page.h
> --- uvm/uvm_page.h	13 May 2024 01:15:53 -0000	1.71
> +++ uvm/uvm_page.h	2 Feb 2025 19:06:19 -0000
> @@ -85,28 +85,31 @@
>   *	and offset to which this page belongs (for pageout),
>   *	and sundry status bits.
>   *
> - *	Fields in this structure are possibly locked by the lock on the page
> - *	queues (P).
> + * Locks used to protect struct members in this file:
> + *	I	immutable after creation
> + *	a	atomic operations
> + *	Q	uvm.pageqlock
> + *	F	uvm.fpageqlock
> + *	o	owner lock (uobject->vmobjlock or uanon->an_lock)
>   */
>  
>  TAILQ_HEAD(pglist, vm_page);
>  
>  struct vm_page {
> -	TAILQ_ENTRY(vm_page)	pageq;		/* queue info for FIFO
> -						 * queue or free list (P) */
> -	RBT_ENTRY(vm_page)	objt;		/* object tree */
> +	TAILQ_ENTRY(vm_page)	pageq;		/* [Q] LRU or free page queue */
> +	RBT_ENTRY(vm_page)	objt;		/* [o] object tree */
>  
> -	struct vm_anon		*uanon;		/* anon (P) */
> -	struct uvm_object	*uobject;	/* object (P) */
> -	voff_t			offset;		/* offset into object (P) */
> +	struct vm_anon		*uanon;		/* [o] anon */
> +	struct uvm_object	*uobject;	/* [o] object */
> +	voff_t			offset;		/* [o] offset into object */
>  
> -	u_int			pg_flags;	/* object flags [P] */
> +	uint32_t		pg_flags;	/* [a] object flags */
>  
> -	u_int			pg_version;	/* version count */
> -	u_int			wire_count;	/* wired down map refs [P] */
> +	uint32_t		pg_version;	/* version count */
> +	uint32_t		wire_count;	/* [o] wired down map refs */
>  
> -	paddr_t			phys_addr;	/* physical address of page */
> -	psize_t			fpgsz;		/* free page range size */
> +	paddr_t			phys_addr;	/* [I] physical address */
> +	psize_t			fpgsz;		/* [F] free page range size */
>  
>  	struct vm_page_md	mdpage;		/* pmap-specific data */
>  
> @@ -287,9 +290,9 @@ int		vm_physseg_find(paddr_t, int *);
>  
>  #define	UVM_PAGEZERO_TARGET	(uvmexp.free / 8)
>  
> -#define VM_PAGE_TO_PHYS(entry)	((entry)->phys_addr)
> +#define VM_PAGE_TO_PHYS(pg)	((pg)->phys_addr)
>  
> -#define VM_PAGE_IS_FREE(entry)  ((entry)->pg_flags & PQ_FREE)
> +#define VM_PAGE_IS_FREE(pg)  ((pg)->pg_flags & PQ_FREE)
>  
>  #define	PADDR_IS_DMA_REACHABLE(paddr)	\
>  	(dma_constraint.ucr_low <= paddr && dma_constraint.ucr_high > paddr)
> 
> 
>