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Newest uvm_purge() to try
> Date: Thu, 22 May 2025 11:58:38 +0200
> From: Martin Pieuchot <mpi@grenadille.net>
>
> Here's the latest version incorporating kettenis@'s pmap_purge() and
> claudio@'s feedbacks. I observed a performance improvement of 10-15%
> on workloads using 24 to 48 CPUs. %sys time obviously increases now
> that tearing down the VM space is accounted for.
>
> Please test and report back.
Going to play with this!
I have a question I wanted to ask about the diff though...
> Index: kern/kern_exit.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/kern_exit.c,v
> diff -u -p -r1.248 kern_exit.c
> --- kern/kern_exit.c 21 May 2025 09:42:59 -0000 1.248
> +++ kern/kern_exit.c 22 May 2025 09:30:43 -0000
> @@ -242,9 +242,14 @@ exit1(struct proc *p, int xexit, int xsi
> if (pr->ps_pptr->ps_sigacts->ps_sigflags & SAS_NOCLDWAIT)
> atomic_setbits_int(&pr->ps_flags, PS_NOZOMBIE);
>
> -#ifdef __HAVE_PMAP_PURGE
> - pmap_purge(p);
> + /* Teardown the virtual address space. */
> + if ((p->p_flag & P_SYSTEM) == 0) {
> +#ifdef MULTIPROCESSOR
> + __mp_release_all(&kernel_lock);
Why do we need an __mp_release_all() here? Is that because we have
multiple paths into exit1() that have different recurse counts for the
kernel lock?
> #endif
> + uvm_purge();
> + KERNEL_LOCK();
> + }
> }
>
> p->p_fd = NULL; /* zap the thread's copy */
> Index: uvm/uvm_extern.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_extern.h,v
> diff -u -p -r1.183 uvm_extern.h
> --- uvm/uvm_extern.h 21 May 2025 16:59:32 -0000 1.183
> +++ uvm/uvm_extern.h 22 May 2025 09:30:43 -0000
> @@ -268,6 +268,7 @@ int uvm_fault(vm_map_t, vaddr_t, vm_fa
>
> vaddr_t uvm_uarea_alloc(void);
> void uvm_uarea_free(struct proc *);
> +void uvm_purge(void);
> void uvm_exit(struct process *);
> void uvm_init_limits(struct plimit *);
> boolean_t uvm_kernacc(caddr_t, size_t, int);
> @@ -401,6 +402,7 @@ void uvmspace_init(struct vmspace *, s
> void uvmspace_exec(struct proc *, vaddr_t, vaddr_t);
> struct vmspace *uvmspace_fork(struct process *);
> void uvmspace_addref(struct vmspace *);
> +void uvmspace_purge(struct vmspace *);
> void uvmspace_free(struct vmspace *);
> struct vmspace *uvmspace_share(struct process *);
> int uvm_sysctl(int *, u_int, void *, size_t *,
> Index: uvm/uvm_glue.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_glue.c,v
> diff -u -p -r1.90 uvm_glue.c
> --- uvm/uvm_glue.c 20 May 2025 07:02:20 -0000 1.90
> +++ uvm/uvm_glue.c 22 May 2025 09:30:43 -0000
> @@ -286,6 +286,25 @@ uvm_uarea_free(struct proc *p)
> }
>
> /*
> + * uvm_purge: teardown a virtual address space.
> + *
> + * If multi-threaded, must be called by the last thread of a process.
> + */
> +void
> +uvm_purge(void)
> +{
> + struct proc *p = curproc;
> + struct vmspace *vm = p->p_vmspace;
> +
> + KERNEL_ASSERT_UNLOCKED();
> +
> +#ifdef __HAVE_PMAP_PURGE
> + pmap_purge(p);
> +#endif
> + uvmspace_purge(vm);
> +}
> +
> +/*
> * uvm_exit: exit a virtual address space
> */
> void
> Index: uvm/uvm_map.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_map.c,v
> diff -u -p -r1.344 uvm_map.c
> --- uvm/uvm_map.c 21 May 2025 16:59:32 -0000 1.344
> +++ uvm/uvm_map.c 22 May 2025 09:43:53 -0000
> @@ -2491,6 +2491,24 @@ uvm_map_teardown(struct vm_map *map)
> entry = TAILQ_NEXT(entry, dfree.deadq);
> }
>
> +#ifdef VMMAP_DEBUG
> + numt = numq = 0;
> + RBT_FOREACH(entry, uvm_map_addr, &map->addr)
> + numt++;
> + TAILQ_FOREACH(entry, &dead_entries, dfree.deadq)
> + numq++;
> + KASSERT(numt == numq);
> + /*
> + * Let VMMAP_DEBUG checks work on an empty map if uvm_map_teardown()
> + * is called twice.
> + */
> + map->size = 0;
> + map->min_offset = 0;
> + map->max_offset = 0;
> + map->flags &= ~VM_MAP_ISVMSPACE;
> +#endif
> + /* reinit RB tree since the above removal leaves the tree corrupted. */
> + RBT_INIT(uvm_map_addr, &map->addr);
> vm_map_unlock(map);
>
> /* Remove address selectors. */
> @@ -2503,18 +2521,7 @@ uvm_map_teardown(struct vm_map *map)
> uvm_addr_destroy(map->uaddr_brk_stack);
> map->uaddr_brk_stack = NULL;
>
> -#ifdef VMMAP_DEBUG
> - numt = numq = 0;
> - RBT_FOREACH(entry, uvm_map_addr, &map->addr)
> - numt++;
> - TAILQ_FOREACH(entry, &dead_entries, dfree.deadq)
> - numq++;
> - KASSERT(numt == numq);
> -#endif
> uvm_unmap_detach(&dead_entries, 0);
> -
> - pmap_destroy(map->pmap);
> - map->pmap = NULL;
> }
>
> /*
> @@ -3395,6 +3402,24 @@ uvmspace_addref(struct vmspace *vm)
> atomic_inc_int(&vm->vm_refcnt);
> }
>
> +void
> +uvmspace_purge(struct vmspace *vm)
> +{
> +#ifdef SYSVSHM
> + /* Get rid of any SYSV shared memory segments. */
> + if (vm->vm_shm != NULL) {
> + KERNEL_LOCK();
> + shmexit(vm);
> + KERNEL_UNLOCK();
> + }
> +#endif
> + /*
> + * Lock the map, to wait out all other references to it. delete
> + * all of the mappings and pages they hold.
> + */
> + uvm_map_teardown(&vm->vm_map);
> +}
> +
> /*
> * uvmspace_free: free a vmspace data structure
> */
> @@ -3403,20 +3428,15 @@ uvmspace_free(struct vmspace *vm)
> {
> if (atomic_dec_int_nv(&vm->vm_refcnt) == 0) {
> /*
> - * lock the map, to wait out all other references to it. delete
> - * all of the mappings and pages they hold, then call the pmap
> - * module to reclaim anything left.
> + * Sanity check. Kernel threads never end up here and
> + * userland ones allready teardown there VM space in
> + * exit1().
> */
> -#ifdef SYSVSHM
> - /* Get rid of any SYSV shared memory segments. */
> - if (vm->vm_shm != NULL) {
> - KERNEL_LOCK();
> - shmexit(vm);
> - KERNEL_UNLOCK();
> - }
> -#endif
> + uvmspace_purge(vm);
> +
> + pmap_destroy(vm->vm_map.pmap);
> + vm->vm_map.pmap = NULL;
>
> - uvm_map_teardown(&vm->vm_map);
> pool_put(&uvm_vmspace_pool, vm);
> }
> }
>
>
>
Newest uvm_purge() to try