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[90.233.218.120]) by smtp.gmail.com with ESMTPSA id o1-20020ac25e21000000b004979db5aa5bsm584933lfg.223.2022.12.23.08.42.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Dec 2022 08:42:33 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Fri, 23 Dec 2022 17:42:30 +0100 To: Lorenzo Stoakes Cc: "Uladzislau Rezki (Sony)" , Andrew Morton , linux-mm@kvack.org, LKML , Baoquan He , Christoph Hellwig , Matthew Wilcox , Nicholas Piggin , Oleksiy Avramchenko , Roman Gushchin Subject: Re: [PATCH v3 1/3] mm: vmalloc: Avoid calling __find_vmap_area() twice in __vunmap() Message-ID: References: <20221222190022.134380-1-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 22, 2022 at 08:06:11PM +0000, Lorenzo Stoakes wrote: > n Thu, Dec 22, 2022 at 08:00:20PM +0100, Uladzislau Rezki (Sony) wrote: > > Currently the __vunmap() path calls __find_vmap_area() twice. Once on > > entry to check that the area exists, then inside the remove_vm_area() > > function which also performs a new search for the VA. > > > > In order to improvie it from a performance point of view we split > > remove_vm_area() into two new parts: > > - find_unlink_vmap_area() that does a search and unlink from tree; > > - __remove_vm_area() that removes without searching. > > > > In this case there is no any functional change for remove_vm_area() > > whereas vm_remove_mappings(), where a second search happens, switches > > to the __remove_vm_area() variant where the already detached VA is > > passed as a parameter, so there is no need to find it again. > > > > Performance wise, i use test_vmalloc.sh with 32 threads doing alloc > > free on a 64-CPUs-x86_64-box: > > > > perf without this patch: > > - 31.41% 0.50% vmalloc_test/10 [kernel.vmlinux] [k] __vunmap > > - 30.92% __vunmap > > - 17.67% _raw_spin_lock > > native_queued_spin_lock_slowpath > > - 12.33% remove_vm_area > > - 11.79% free_vmap_area_noflush > > - 11.18% _raw_spin_lock > > native_queued_spin_lock_slowpath > > 0.76% free_unref_page > > > > perf with this patch: > > - 11.35% 0.13% vmalloc_test/14 [kernel.vmlinux] [k] __vunmap > > - 11.23% __vunmap > > - 8.28% find_unlink_vmap_area > > - 7.95% _raw_spin_lock > > 7.44% native_queued_spin_lock_slowpath > > - 1.93% free_vmap_area_noflush > > - 0.56% _raw_spin_lock > > 0.53% native_queued_spin_lock_slowpath > > 0.60% __vunmap_range_noflush > > > > __vunmap() consumes around ~20% less CPU cycles on this test. > > > > v2 -> v3: > > - update commit message; > > - rename the vm_remove_mappings() to the va_remove_mappings(); > > - move va-unlinking to the callers so the free_vmap_area_noflush() > > now expects a VA that has been disconnected; > > - eliminate a local variable in the remove_vm_area(). > > > > Reported-by: Roman Gushchin > > Signed-off-by: Uladzislau Rezki (Sony) > > --- > > mm/vmalloc.c | 77 ++++++++++++++++++++++++++++++++-------------------- > > 1 file changed, 47 insertions(+), 30 deletions(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 9e30f0b39203..eb91ecaa7277 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1815,9 +1815,9 @@ static void drain_vmap_area_work(struct work_struct *work) > > } > > > > /* > > - * Free a vmap area, caller ensuring that the area has been unmapped > > - * and flush_cache_vunmap had been called for the correct range > > - * previously. > > + * Free a vmap area, caller ensuring that the area has been unmapped, > > + * unlinked and flush_cache_vunmap had been called for the correct > > + * range previously. > > */ > > static void free_vmap_area_noflush(struct vmap_area *va) > > { > > @@ -1825,9 +1825,8 @@ static void free_vmap_area_noflush(struct vmap_area *va) > > unsigned long va_start = va->va_start; > > unsigned long nr_lazy; > > > > - spin_lock(&vmap_area_lock); > > - unlink_va(va, &vmap_area_root); > > - spin_unlock(&vmap_area_lock); > > + if (WARN_ON_ONCE(!list_empty(&va->list))) > > + return; > > > > nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >> > > PAGE_SHIFT, &vmap_lazy_nr); > > @@ -1871,6 +1870,19 @@ struct vmap_area *find_vmap_area(unsigned long addr) > > return va; > > } > > > > +static struct vmap_area *find_unlink_vmap_area(unsigned long addr) > > +{ > > + struct vmap_area *va; > > + > > + spin_lock(&vmap_area_lock); > > + va = __find_vmap_area(addr, &vmap_area_root); > > + if (va) > > + unlink_va(va, &vmap_area_root); > > + spin_unlock(&vmap_area_lock); > > + > > + return va; > > +} > > + > > /*** Per cpu kva allocator ***/ > > > > /* > > @@ -2015,6 +2027,10 @@ static void free_vmap_block(struct vmap_block *vb) > > tmp = xa_erase(&vmap_blocks, addr_to_vb_idx(vb->va->va_start)); > > BUG_ON(tmp != vb); > > > > + spin_lock(&vmap_area_lock); > > + unlink_va(vb->va, &vmap_area_root); > > + spin_unlock(&vmap_area_lock); > > + > > free_vmap_area_noflush(vb->va); > > kfree_rcu(vb, rcu_head); > > } > > @@ -2591,6 +2607,20 @@ struct vm_struct *find_vm_area(const void *addr) > > return va->vm; > > } > > > > +static struct vm_struct *__remove_vm_area(struct vmap_area *va) > > +{ > > + struct vm_struct *vm; > > + > > + if (!va || !va->vm) > > + return NULL; > > + > > + vm = va->vm; > > + kasan_free_module_shadow(vm); > > + free_unmap_vmap_area(va); > > + > > + return vm; > > +} > > + > > /** > > * remove_vm_area - find and remove a continuous kernel virtual area > > * @addr: base address > > @@ -2603,26 +2633,10 @@ struct vm_struct *find_vm_area(const void *addr) > > */ > > struct vm_struct *remove_vm_area(const void *addr) > > { > > - struct vmap_area *va; > > - > > might_sleep(); > > > > - spin_lock(&vmap_area_lock); > > - va = __find_vmap_area((unsigned long)addr, &vmap_area_root); > > - if (va && va->vm) { > > - struct vm_struct *vm = va->vm; > > - > > - va->vm = NULL; > > - spin_unlock(&vmap_area_lock); > > - > > - kasan_free_module_shadow(vm); > > - free_unmap_vmap_area(va); > > - > > - return vm; > > - } > > - > > - spin_unlock(&vmap_area_lock); > > - return NULL; > > + return __remove_vm_area( > > + find_unlink_vmap_area((unsigned long) addr)); > > } > > > > static inline void set_area_direct_map(const struct vm_struct *area, > > @@ -2636,16 +2650,17 @@ static inline void set_area_direct_map(const struct vm_struct *area, > > set_direct_map(area->pages[i]); > > } > > > > -/* Handle removing and resetting vm mappings related to the vm_struct. */ > > -static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages) > > +/* Handle removing and resetting vm mappings related to the VA's vm_struct. */ > > +static void va_remove_mappings(struct vmap_area *va, int deallocate_pages) > > { > > + struct vm_struct *area = va->vm; > > unsigned long start = ULONG_MAX, end = 0; > > unsigned int page_order = vm_area_page_order(area); > > int flush_reset = area->flags & VM_FLUSH_RESET_PERMS; > > int flush_dmap = 0; > > int i; > > > > - remove_vm_area(area->addr); > > + __remove_vm_area(va); > > > > /* If this is not VM_FLUSH_RESET_PERMS memory, no need for the below. */ > > if (!flush_reset) > > @@ -2690,6 +2705,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages) > > static void __vunmap(const void *addr, int deallocate_pages) > > { > > struct vm_struct *area; > > + struct vmap_area *va; > > > > if (!addr) > > return; > > @@ -2698,19 +2714,20 @@ static void __vunmap(const void *addr, int deallocate_pages) > > addr)) > > return; > > > > - area = find_vm_area(addr); > > - if (unlikely(!area)) { > > + va = find_unlink_vmap_area((unsigned long)addr); > > + if (unlikely(!va)) { > > 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)); > > > > kasan_poison_vmalloc(area->addr, get_vm_area_size(area)); > > > > - vm_remove_mappings(area, deallocate_pages); > > + va_remove_mappings(va, deallocate_pages); > > > > if (deallocate_pages) { > > int i; > > -- > > 2.30.2 > > > > All looks good to me! Great work! Feel free to add the below to all patches in series:- > > Reviewed-by: Lorenzo Stoakes > Added :) Thank you for review! -- Uladzislau Rezki