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Mon, 27 Mar 2023 23:26:00 -0400 X-MC-Unique: lX-b4PxfNYqFoeXGWdCARA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 95AC8801779; Tue, 28 Mar 2023 03:25:59 +0000 (UTC) Received: from localhost (ovpn-12-210.pek2.redhat.com [10.72.12.210]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 39FC3FD6E; Tue, 28 Mar 2023 03:25:57 +0000 (UTC) Date: Tue, 28 Mar 2023 11:25:54 +0800 From: Baoquan He To: "Uladzislau Rezki (Sony)" Cc: Andrew Morton , linux-mm@kvack.org, LKML , Lorenzo Stoakes , Christoph Hellwig , Matthew Wilcox , Dave Chinner , Oleksiy Avramchenko Subject: Re: [PATCH v3 1/2] mm: vmalloc: Remove a global vmap_blocks xarray Message-ID: References: <20230327170126.406044-1-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230327170126.406044-1-urezki@gmail.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8953420003 X-Stat-Signature: nx6p7n4med71oiiwwqfpxzsrojurcg1b X-Rspam-User: X-HE-Tag: 1679973966-444896 X-HE-Meta: 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 4AGIlVJn tUCdbbdFxpG37ZA1cDKqNZb3gAQ3uOG8ASz6ViPuWng/QGa4goevrwy4AKmDVYsOsQtu1zAnd5D5NLZ50htzrR5Rbu1mV1wk+gK5G+Sj4Xz3iNiZTWBO9Eez3N1ZJXqJwcEqrr281Mogfdhoms6b1M/fFlEu3MiAt7x5b8pW9oFr0UeMAkt/jsW71sYHNh2A5rEk8jlH//26tnvI0nwIfeWfoukP01axH1AM3v5s2L11L9I0R8ZNF+E5ANOEHirUE8k/a7Vw0C2MJZGO03Olp8n0iSQi62TLfLHr9 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03/27/23 at 07:01pm, Uladzislau Rezki (Sony) wrote: > A global vmap_blocks-xarray array can be contented under > heavy usage of the vm_map_ram()/vm_unmap_ram() APIs. The > lock_stat shows that a "vmap_blocks.xa_lock" lock is a > second in a top-list when it comes to contentions: > > > ---------------------------------------- > class name con-bounces contentions ... > ---------------------------------------- > vmap_area_lock: 2554079 2554276 ... > -------------- > vmap_area_lock 1297948 [<00000000dd41cbaa>] alloc_vmap_area+0x1c7/0x910 > vmap_area_lock 1256330 [<000000009d927bf3>] free_vmap_block+0x4a/0xe0 > vmap_area_lock 1 [<00000000c95c05a7>] find_vm_area+0x16/0x70 > -------------- > vmap_area_lock 1738590 [<00000000dd41cbaa>] alloc_vmap_area+0x1c7/0x910 > vmap_area_lock 815688 [<000000009d927bf3>] free_vmap_block+0x4a/0xe0 > vmap_area_lock 1 [<00000000c1d619d7>] __get_vm_area_node+0xd2/0x170 > > vmap_blocks.xa_lock: 862689 862698 ... > ------------------- > vmap_blocks.xa_lock 378418 [<00000000625a5626>] vm_map_ram+0x359/0x4a0 > vmap_blocks.xa_lock 484280 [<00000000caa2ef03>] xa_erase+0xe/0x30 > ------------------- > vmap_blocks.xa_lock 576226 [<00000000caa2ef03>] xa_erase+0xe/0x30 > vmap_blocks.xa_lock 286472 [<00000000625a5626>] vm_map_ram+0x359/0x4a0 > ... > > > that is a result of running vm_map_ram()/vm_unmap_ram() in > a loop. The test creates 64(on 64 CPUs system) threads and > each one maps/unmaps 1 page. With my understanding, the xarray will take more time when calling xa_insert() or xa_erase() because these two will cause xa_expand() and xa_shrink() if the index is sparse. xa_load() should be low cost to finish. Wondering if in your testing code, the mapping address is close or too far. 1 mm/vmalloc.c <> err = xa_insert(&vmap_blocks, vb_idx, vb, gfp_mask); 2 mm/vmalloc.c <> tmp = xa_erase(&vmap_blocks, addr_to_vb_idx(vb->va->va_start)); 3 mm/vmalloc.c <> vb = xa_load(&vmap_blocks, addr_to_vb_idx(addr)); 4 mm/vmalloc.c <> vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long )addr)); > > After this change the "xa_lock" can be considered as a noise > in the same test condition: > > > ... > &xa->xa_lock#1: 10333 10394 ... > -------------- > &xa->xa_lock#1 5349 [<00000000bbbc9751>] xa_erase+0xe/0x30 > &xa->xa_lock#1 5045 [<0000000018def45d>] vm_map_ram+0x3a4/0x4f0 > -------------- > &xa->xa_lock#1 7326 [<0000000018def45d>] vm_map_ram+0x3a4/0x4f0 > &xa->xa_lock#1 3068 [<00000000bbbc9751>] xa_erase+0xe/0x30 > ... > > > This patch does not fix vmap_area_lock/free_vmap_area_lock and > purge_vmap_area_lock bottle-necks, it is rather a separate rework. > > v1 - v2: > - Add more comments(Andrew Morton req.) > - Switch to WARN_ON_ONCE(Lorenzo Stoakes req.) > > v2 -> v3: > - Fix a kernel-doc complain(Matthew Wilcox) > > Signed-off-by: Uladzislau Rezki (Sony) > --- > mm/vmalloc.c | 85 +++++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 64 insertions(+), 21 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 978194dc2bb8..821256ecf81c 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1908,9 +1908,22 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr) > #define VMAP_BLOCK 0x2 /* mark out the vmap_block sub-type*/ > #define VMAP_FLAGS_MASK 0x3 > > +/* > + * We should probably have a fallback mechanism to allocate virtual memory > + * out of partially filled vmap blocks. However vmap block sizing should be > + * fairly reasonable according to the vmalloc size, so it shouldn't be a > + * big problem. > + */ > struct vmap_block_queue { > spinlock_t lock; > struct list_head free; > + > + /* > + * An xarray requires an extra memory dynamically to > + * be allocated. If it is an issue, we can use rb-tree > + * instead. > + */ > + struct xarray vmap_blocks; > }; > > struct vmap_block { > @@ -1928,24 +1941,46 @@ struct vmap_block { > static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue); > > /* > - * XArray of vmap blocks, indexed by address, to quickly find a vmap block > - * in the free path. Could get rid of this if we change the API to return a > - * "cookie" from alloc, to be passed to free. But no big deal yet. > + * In order to fast access to any "vmap_block" associated with a > + * specific address, we store them into a per-cpu xarray. A hash > + * function is addr_to_vbq() whereas a key is a vb->va->va_start > + * value. > + * > + * Please note, a vmap_block_queue, which is a per-cpu, is not > + * serialized by a raw_smp_processor_id() current CPU, instead > + * it is chosen based on a CPU-index it belongs to, i.e. it is > + * a hash-table. > + * > + * An example: > + * > + * CPU_1 CPU_2 CPU_0 > + * | | | > + * V V V > + * 0 10 20 30 40 50 60 > + * |------|------|------|------|------|------|... > + * CPU0 CPU1 CPU2 CPU0 CPU1 CPU2 > + * > + * - CPU_1 invokes vm_unmap_ram(6), 6 belongs to CPU0 zone, thus > + * it access: CPU0/INDEX0 -> vmap_blocks -> xa_lock; > + * > + * - CPU_2 invokes vm_unmap_ram(11), 11 belongs to CPU1 zone, thus > + * it access: CPU1/INDEX1 -> vmap_blocks -> xa_lock; > + * > + * - CPU_0 invokes vm_unmap_ram(20), 20 belongs to CPU2 zone, thus > + * it access: CPU2/INDEX2 -> vmap_blocks -> xa_lock. > */ > -static DEFINE_XARRAY(vmap_blocks); > +static struct vmap_block_queue * > +addr_to_vbq(unsigned long addr) > +{ > + int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > > -/* > - * We should probably have a fallback mechanism to allocate virtual memory > - * out of partially filled vmap blocks. However vmap block sizing should be > - * fairly reasonable according to the vmalloc size, so it shouldn't be a > - * big problem. > - */ > + return &per_cpu(vmap_block_queue, index); > +} > > -static unsigned long addr_to_vb_idx(unsigned long addr) > +static unsigned long > +addr_to_vb_va_start(unsigned long addr) > { > - addr -= VMALLOC_START & ~(VMAP_BLOCK_SIZE-1); > - addr /= VMAP_BLOCK_SIZE; > - return addr; > + return rounddown(addr, VMAP_BLOCK_SIZE); > } > > static void *vmap_block_vaddr(unsigned long va_start, unsigned long pages_off) > @@ -1953,7 +1988,7 @@ static void *vmap_block_vaddr(unsigned long va_start, unsigned long pages_off) > unsigned long addr; > > addr = va_start + (pages_off << PAGE_SHIFT); > - BUG_ON(addr_to_vb_idx(addr) != addr_to_vb_idx(va_start)); > + WARN_ON_ONCE(addr_to_vb_va_start(addr) != va_start); > return (void *)addr; > } > > @@ -1970,7 +2005,6 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) > struct vmap_block_queue *vbq; > struct vmap_block *vb; > struct vmap_area *va; > - unsigned long vb_idx; > int node, err; > void *vaddr; > > @@ -2003,8 +2037,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) > bitmap_set(vb->used_map, 0, (1UL << order)); > INIT_LIST_HEAD(&vb->free_list); > > - vb_idx = addr_to_vb_idx(va->va_start); > - err = xa_insert(&vmap_blocks, vb_idx, vb, gfp_mask); > + vbq = addr_to_vbq(va->va_start); > + err = xa_insert(&vbq->vmap_blocks, va->va_start, vb, gfp_mask); Using va->va_start as index to access xarray may cost extra memory. Imagine we got a virtual address at VMALLOC_START, its region is [VMALLOC_START, VMALLOC_START+4095]. In the xarray, its sequence order is 0. While with va->va_start, it's 0xffffc90000000000UL on x86_64 with level4 paging mode. That means for the first page size vmalloc area, storing it into xarray need about 10 levels of xa_node, just for the one page size. With the old addr_to_vb_idx(), its index is 0. Only one level height is needed. One xa_node is about 72bytes, it could take more time and memory to access va->va_start. Not sure if my understanding is correct. static unsigned long addr_to_vb_idx(unsigned long addr) { addr -= VMALLOC_START & ~(VMAP_BLOCK_SIZE-1); addr /= VMAP_BLOCK_SIZE; return addr; } > if (err) { > kfree(vb); > free_vmap_area(va); > @@ -2021,9 +2055,11 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) > > static void free_vmap_block(struct vmap_block *vb) > { > + struct vmap_block_queue *vbq; > struct vmap_block *tmp; > > - tmp = xa_erase(&vmap_blocks, addr_to_vb_idx(vb->va->va_start)); > + vbq = addr_to_vbq(vb->va->va_start); > + tmp = xa_erase(&vbq->vmap_blocks, vb->va->va_start); > BUG_ON(tmp != vb); > > spin_lock(&vmap_area_lock); > @@ -2135,6 +2171,7 @@ static void vb_free(unsigned long addr, unsigned long size) > unsigned long offset; > unsigned int order; > struct vmap_block *vb; > + struct vmap_block_queue *vbq; > > BUG_ON(offset_in_page(size)); > BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC); > @@ -2143,7 +2180,10 @@ static void vb_free(unsigned long addr, unsigned long size) > > order = get_order(size); > offset = (addr & (VMAP_BLOCK_SIZE - 1)) >> PAGE_SHIFT; > - vb = xa_load(&vmap_blocks, addr_to_vb_idx(addr)); > + > + vbq = addr_to_vbq(addr); > + vb = xa_load(&vbq->vmap_blocks, addr_to_vb_va_start(addr)); > + > spin_lock(&vb->lock); > bitmap_clear(vb->used_map, offset, (1UL << order)); > spin_unlock(&vb->lock); > @@ -3486,6 +3526,7 @@ static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags > { > char *start; > struct vmap_block *vb; > + struct vmap_block_queue *vbq; > unsigned long offset; > unsigned int rs, re, n; > > @@ -3503,7 +3544,8 @@ static void vmap_ram_vread(char *buf, char *addr, int count, unsigned long flags > * Area is split into regions and tracked with vmap_block, read out > * each region and zero fill the hole between regions. > */ > - vb = xa_load(&vmap_blocks, addr_to_vb_idx((unsigned long)addr)); > + vbq = addr_to_vbq((unsigned long) addr); > + vb = xa_load(&vbq->vmap_blocks, addr_to_vb_va_start((unsigned long) addr)); > if (!vb) > goto finished; > > @@ -4272,6 +4314,7 @@ void __init vmalloc_init(void) > p = &per_cpu(vfree_deferred, i); > init_llist_head(&p->list); > INIT_WORK(&p->wq, delayed_vfree_work); > + xa_init(&vbq->vmap_blocks); > } > > /* Import existing vmlist entries. */ > -- > 2.30.2 >