| Message ID | 20190417194002.12369-2-guro@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vmalloc enhancements | expand |
On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrote: > __vunmap() calls find_vm_area() twice without an obvious reason: > first directly to get the area pointer, second indirectly by calling > remove_vm_area(), which is again searching for the area. > > To remove this redundancy, let's split remove_vm_area() into > __remove_vm_area(struct vmap_area *), which performs the actual area > removal, and remove_vm_area(const void *addr) wrapper, which can > be used everywhere, where it has been used before. > > On my test setup, I've got 5-10% speed up on vfree()'ing 1000000 > of 4-pages vmalloc blocks. > > Perf report before: > 22.64% cat [kernel.vmlinux] [k] free_pcppages_bulk > 10.30% cat [kernel.vmlinux] [k] __vunmap > 9.80% cat [kernel.vmlinux] [k] find_vmap_area > 8.11% cat [kernel.vmlinux] [k] vunmap_page_range > 4.20% cat [kernel.vmlinux] [k] __slab_free > 3.56% cat [kernel.vmlinux] [k] __list_del_entry_valid > 3.46% cat [kernel.vmlinux] [k] smp_call_function_many > 3.33% cat [kernel.vmlinux] [k] kfree > 3.32% cat [kernel.vmlinux] [k] free_unref_page > > Perf report after: > 23.01% cat [kernel.kallsyms] [k] free_pcppages_bulk > 9.46% cat [kernel.kallsyms] [k] __vunmap > 9.15% cat [kernel.kallsyms] [k] vunmap_page_range > 6.17% cat [kernel.kallsyms] [k] __slab_free > 5.61% cat [kernel.kallsyms] [k] kfree > 4.86% cat [kernel.kallsyms] [k] bad_range > 4.67% cat [kernel.kallsyms] [k] free_unref_page_commit > 4.24% cat [kernel.kallsyms] [k] __list_del_entry_valid > 3.68% cat [kernel.kallsyms] [k] free_unref_page > 3.65% cat [kernel.kallsyms] [k] __list_add_valid > 3.19% cat [kernel.kallsyms] [k] __purge_vmap_area_lazy > 3.10% cat [kernel.kallsyms] [k] find_vmap_area > 3.05% cat [kernel.kallsyms] [k] rcu_cblist_dequeue > > ... > > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2068,6 +2068,24 @@ struct vm_struct *find_vm_area(const void *addr) > return NULL; > } > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > +{ > + struct vm_struct *vm = va->vm; > + > + might_sleep(); Where might __remove_vm_area() sleep? From a quick scan I'm only seeing vfree(), and that has the might_sleep_if(!in_interrupt()). So perhaps we can remove this... > + spin_lock(&vmap_area_lock); > + va->vm = NULL; > + va->flags &= ~VM_VM_AREA; > + va->flags |= VM_LAZY_FREE; > + spin_unlock(&vmap_area_lock); > + > + kasan_free_shadow(vm); > + free_unmap_vmap_area(va); > + > + return vm; > +} > +
On Wed, Apr 17, 2019 at 02:58:27PM -0700, Andrew Morton wrote: > On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrote: > > > __vunmap() calls find_vm_area() twice without an obvious reason: > > first directly to get the area pointer, second indirectly by calling > > remove_vm_area(), which is again searching for the area. > > > > To remove this redundancy, let's split remove_vm_area() into > > __remove_vm_area(struct vmap_area *), which performs the actual area > > removal, and remove_vm_area(const void *addr) wrapper, which can > > be used everywhere, where it has been used before. > > > > On my test setup, I've got 5-10% speed up on vfree()'ing 1000000 > > of 4-pages vmalloc blocks. > > > > Perf report before: > > 22.64% cat [kernel.vmlinux] [k] free_pcppages_bulk > > 10.30% cat [kernel.vmlinux] [k] __vunmap > > 9.80% cat [kernel.vmlinux] [k] find_vmap_area > > 8.11% cat [kernel.vmlinux] [k] vunmap_page_range > > 4.20% cat [kernel.vmlinux] [k] __slab_free > > 3.56% cat [kernel.vmlinux] [k] __list_del_entry_valid > > 3.46% cat [kernel.vmlinux] [k] smp_call_function_many > > 3.33% cat [kernel.vmlinux] [k] kfree > > 3.32% cat [kernel.vmlinux] [k] free_unref_page > > > > Perf report after: > > 23.01% cat [kernel.kallsyms] [k] free_pcppages_bulk > > 9.46% cat [kernel.kallsyms] [k] __vunmap > > 9.15% cat [kernel.kallsyms] [k] vunmap_page_range > > 6.17% cat [kernel.kallsyms] [k] __slab_free > > 5.61% cat [kernel.kallsyms] [k] kfree > > 4.86% cat [kernel.kallsyms] [k] bad_range > > 4.67% cat [kernel.kallsyms] [k] free_unref_page_commit > > 4.24% cat [kernel.kallsyms] [k] __list_del_entry_valid > > 3.68% cat [kernel.kallsyms] [k] free_unref_page > > 3.65% cat [kernel.kallsyms] [k] __list_add_valid > > 3.19% cat [kernel.kallsyms] [k] __purge_vmap_area_lazy > > 3.10% cat [kernel.kallsyms] [k] find_vmap_area > > 3.05% cat [kernel.kallsyms] [k] rcu_cblist_dequeue > > > > ... > > > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -2068,6 +2068,24 @@ struct vm_struct *find_vm_area(const void *addr) > > return NULL; > > } > > > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > > +{ > > + struct vm_struct *vm = va->vm; > > + > > + might_sleep(); > > Where might __remove_vm_area() sleep? > > From a quick scan I'm only seeing vfree(), and that has the > might_sleep_if(!in_interrupt()). > > So perhaps we can remove this... Agree. Here is the patch. Thank you! -- From 4adf58e4d3ffe45a542156ca0bce3dc9f6679939 Mon Sep 17 00:00:00 2001 From: Roman Gushchin <guro@fb.com> Date: Wed, 17 Apr 2019 15:55:49 -0700 Subject: [PATCH] mm: remove might_sleep() in __remove_vm_area() __remove_vm_area() has a redundant might_sleep() call, which isn't really required, because the only place it can sleep is vfree() and it already contains might_sleep_if(!in_interrupt()). Suggested-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Roman Gushchin <guro@fb.com> --- mm/vmalloc.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 69a5673c4cd3..4a91acce4b5f 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2079,8 +2079,6 @@ static struct vm_struct *__remove_vm_area(struct vmap_area *va) { struct vm_struct *vm = va->vm; - might_sleep(); - spin_lock(&vmap_area_lock); va->vm = NULL; va->flags &= ~VM_VM_AREA;
On Wed, Apr 17, 2019 at 02:58:27PM -0700, Andrew Morton wrote: > On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrote: > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > > +{ > > + struct vm_struct *vm = va->vm; > > + > > + might_sleep(); > > Where might __remove_vm_area() sleep? > > >From a quick scan I'm only seeing vfree(), and that has the > might_sleep_if(!in_interrupt()). > > So perhaps we can remove this... See commit 5803ed292e63 ("mm: mark all calls into the vmalloc subsystem as potentially sleeping") It looks like the intent is to unconditionally check might_sleep() at the entry points to the vmalloc code, rather than only catch them in the occasional place where it happens to go wrong.
On Thu, 18 Apr 2019 04:18:34 -0700 Matthew Wilcox <willy@infradead.org> wrote: > On Wed, Apr 17, 2019 at 02:58:27PM -0700, Andrew Morton wrote: > > On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrote: > > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > > > +{ > > > + struct vm_struct *vm = va->vm; > > > + > > > + might_sleep(); > > > > Where might __remove_vm_area() sleep? > > > > >From a quick scan I'm only seeing vfree(), and that has the > > might_sleep_if(!in_interrupt()). > > > > So perhaps we can remove this... > > See commit 5803ed292e63 ("mm: mark all calls into the vmalloc subsystem as potentially sleeping") > > It looks like the intent is to unconditionally check might_sleep() at > the entry points to the vmalloc code, rather than only catch them in > the occasional place where it happens to go wrong. afaict, vfree() will only do a mutex_trylock() in try_purge_vmap_area_lazy(). So does vfree actually sleep in any situation? Whether or not local interrupts are enabled?
On 04/18/2019 03:24 PM, Andrew Morton wrote: > afaict, vfree() will only do a mutex_trylock() in > try_purge_vmap_area_lazy(). So does vfree actually sleep in any > situation? Whether or not local interrupts are enabled? We would be in a big trouble if vfree() could potentially sleep... Random example : __free_fdtable() called from rcu callback.
On Thu, Apr 18, 2019 at 03:24:31PM -0700, Andrew Morton wrote: > On Thu, 18 Apr 2019 04:18:34 -0700 Matthew Wilcox <willy@infradead.org> wrote: > > > On Wed, Apr 17, 2019 at 02:58:27PM -0700, Andrew Morton wrote: > > > On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrote: > > > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > > > > +{ > > > > + struct vm_struct *vm = va->vm; > > > > + > > > > + might_sleep(); > > > > > > Where might __remove_vm_area() sleep? > > > > > > >From a quick scan I'm only seeing vfree(), and that has the > > > might_sleep_if(!in_interrupt()). > > > > > > So perhaps we can remove this... > > > > See commit 5803ed292e63 ("mm: mark all calls into the vmalloc subsystem as potentially sleeping") > > > > It looks like the intent is to unconditionally check might_sleep() at > > the entry points to the vmalloc code, rather than only catch them in > > the occasional place where it happens to go wrong. > > afaict, vfree() will only do a mutex_trylock() in > try_purge_vmap_area_lazy(). So does vfree actually sleep in any > situation? Whether or not local interrupts are enabled? IIRC, the original problem that used to prohibit vfree() in interrupts was the use of spinlocks that were used in a lot of places by plain spin_lock(). I'm not sure it could actually sleep in anything not too ancient...
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 92b784d8088c..8ad8e8464e55 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2068,6 +2068,24 @@ struct vm_struct *find_vm_area(const void *addr) return NULL; } +static struct vm_struct *__remove_vm_area(struct vmap_area *va) +{ + struct vm_struct *vm = va->vm; + + might_sleep(); + + spin_lock(&vmap_area_lock); + va->vm = NULL; + va->flags &= ~VM_VM_AREA; + va->flags |= VM_LAZY_FREE; + spin_unlock(&vmap_area_lock); + + kasan_free_shadow(vm); + free_unmap_vmap_area(va); + + return vm; +} + /** * remove_vm_area - find and remove a continuous kernel virtual area * @addr: base address @@ -2080,31 +2098,20 @@ struct vm_struct *find_vm_area(const void *addr) */ struct vm_struct *remove_vm_area(const void *addr) { + struct vm_struct *vm = NULL; struct vmap_area *va; - might_sleep(); - va = find_vmap_area((unsigned long)addr); - if (va && va->flags & VM_VM_AREA) { - struct vm_struct *vm = va->vm; - - spin_lock(&vmap_area_lock); - va->vm = NULL; - va->flags &= ~VM_VM_AREA; - va->flags |= VM_LAZY_FREE; - spin_unlock(&vmap_area_lock); - - kasan_free_shadow(vm); - free_unmap_vmap_area(va); + if (va && va->flags & VM_VM_AREA) + vm = __remove_vm_area(va); - return vm; - } - return NULL; + return vm; } static void __vunmap(const void *addr, int deallocate_pages) { struct vm_struct *area; + struct vmap_area *va; if (!addr) return; @@ -2113,17 +2120,18 @@ static void __vunmap(const void *addr, int deallocate_pages) addr)) return; - area = find_vm_area(addr); - if (unlikely(!area)) { + va = find_vmap_area((unsigned long)addr); + if (unlikely(!va || !(va->flags & VM_VM_AREA))) { WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n", addr); return; } + area = va->vm; debug_check_no_locks_freed(area->addr, get_vm_area_size(area)); debug_check_no_obj_freed(area->addr, get_vm_area_size(area)); - remove_vm_area(addr); + __remove_vm_area(va); if (deallocate_pages) { int i; @@ -2138,7 +2146,6 @@ static void __vunmap(const void *addr, int deallocate_pages) } kfree(area); - return; } static inline void __vfree_deferred(const void *addr)