Messages in this thread Patch in this message | | | From | Roman Gushchin <> | Subject | Re: [PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call to find_vm_area() | Date | Wed, 17 Apr 2019 23:02:25 +0000 |
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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!
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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; -- 2.20.1
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