| Message ID | 20230323192111.1501308-1-urezki@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] mm: vmalloc: Remove a global vmap_blocks xarray | expand |
On Thu, 23 Mar 2023 20:21:11 +0100 "Uladzislau Rezki (Sony)" <urezki@gmail.com> 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: > > ... > > 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. > > ... > > static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue); > > ... > > +static struct vmap_block_queue * > +addr_to_vbq(unsigned long addr) > +{ > + int cpu = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > + return &per_cpu(vmap_block_queue, cpu); > +} Seems strange. vmap_block_queue is not a per-cpu thing in this usage. Instead it's a hash table, indexed off the (hashed) address, not off smp_processor_id(). Yet in other places, vmap_block_queue *is* used in the conventional cpu-local fashion. So we can have CPU A using the cpu-local entry in vmap_block_queue while CPU B is simultaneously using it, having looked it up via `addr'. AFAICT this all works OK, no races. But still, what it's doing is mixing an addr-indexed hashtable with the CPU-indexed array in surprising ways. It would be clearer to make the vmap_blocks array a separate thing from the per-cpu array, although it would presumably use a bit more memory. Can we please at least get a big fat comment in an appropriate place which explains all this to the reader?
On Thu, Mar 23, 2023 at 08:21:11PM +0100, 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: > > <snip> > ---------------------------------------- > 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 > ... > <snip> > > 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. > > After this change the "xa_lock" can be considered as a noise > in the same test condition: > > <snip> > ... > &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 > ... > <snip> > Nice! Really good to see contention reduced, but in addition I'm a huge fan of us removing the global state in vmalloc and this is a good start. I've noticed a small perf regression after 3 runs of ./test_vmalloc.sh performance from an average of 119356136169 cycles to 120404645782 or +0.9% but this doesn't seem especially egregious. > 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. > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> > --- > mm/vmalloc.c | 50 ++++++++++++++++++++++++++------------------------ > 1 file changed, 26 insertions(+), 24 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 978194dc2bb8..13b5342bed9a 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1911,6 +1911,7 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr) > struct vmap_block_queue { > spinlock_t lock; > struct list_head free; > + struct xarray vmap_blocks; > }; > > struct vmap_block { > @@ -1927,25 +1928,18 @@ struct vmap_block { > /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */ > 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. > - */ Doesn't this comment still apply? Or is the idea of returning the "cookie" not really viable? > -static DEFINE_XARRAY(vmap_blocks); > - > -/* > - * 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. > - */ Again, is this comment no longer relevant? > +static struct vmap_block_queue * > +addr_to_vbq(unsigned long addr) > +{ > + int cpu = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > + return &per_cpu(vmap_block_queue, cpu); > +} Andrew's already commented on this, so I won't dwell but it does seem odd to subdivide by number of possible CPUs rather than just use the actual CPU. I guess your response to his question will also answer mine :) > > -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; > + /* A start address of block an address belongs to. */ A nit, but might be worth referring to the assert in vmap_block_vaddr(), as this comment seems a bit redundant otherwise as it is implied by the code it comments. > + return rounddown(addr, VMAP_BLOCK_SIZE); > } > > static void *vmap_block_vaddr(unsigned long va_start, unsigned long pages_off) > @@ -1953,7 +1947,7 @@ 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)); > + BUG_ON(addr_to_vb_va_start(addr) != addr_to_vb_va_start(va_start)); Maybe nitty, but perhaps better to WARN_ON() here to avoid BUG_ON proliferation? And can't this be the below? WARN_ON(addr_to_vb_va_start(addr) != va_start); > return (void *)addr; > } > > @@ -1970,7 +1964,6 @@ 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 +1996,8 @@ 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); This seems actually like a nice subtle improvement in that we are now indexing always on va_start explicitly and will always load using addr_to_vb_va_start(). > if (err) { > kfree(vb); > free_vmap_area(va); > @@ -2021,9 +2014,11 @@ 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 +2130,7 @@ 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 +2139,10 @@ 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 +3485,7 @@ 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 +3503,8 @@ 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 +4273,7 @@ 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 >
On Thu, Mar 23, 2023 at 02:12:53PM -0700, Andrew Morton wrote: > On Thu, 23 Mar 2023 20:21:11 +0100 "Uladzislau Rezki (Sony)" <urezki@gmail.com> 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: > > > > ... > > > > 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. > > > > ... > > > > static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue); > > > > ... > > > > +static struct vmap_block_queue * > > +addr_to_vbq(unsigned long addr) > > +{ > > + int cpu = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > > + return &per_cpu(vmap_block_queue, cpu); > > +} > > Seems strange. vmap_block_queue is not a per-cpu thing in this usage. > Instead it's a hash table, indexed off the (hashed) address, not off > smp_processor_id(). > > Yet in other places, vmap_block_queue *is* used in the conventional > cpu-local fashion. > > So we can have CPU A using the cpu-local entry in vmap_block_queue > while CPU B is simultaneously using it, having looked it up via `addr'. > > AFAICT this all works OK, no races. > > But still, what it's doing is mixing an addr-indexed hashtable with the > CPU-indexed array in surprising ways. It would be clearer to make the > vmap_blocks array a separate thing from the per-cpu array, although it > would presumably use a bit more memory. > > Can we please at least get a big fat comment in an appropriate place > which explains all this to the reader? > Yep, i will send out a v2 with all explanation. Indeed i have to add detailed explanation. Thanks! -- Uladzislau Rezki
On Thu, Mar 23, 2023 at 09:46:00PM +0000, Lorenzo Stoakes wrote: > On Thu, Mar 23, 2023 at 08:21:11PM +0100, 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: > > > > <snip> > > ---------------------------------------- > > 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 > > ... > > <snip> > > > > 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. > > > > After this change the "xa_lock" can be considered as a noise > > in the same test condition: > > > > <snip> > > ... > > &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 > > ... > > <snip> > > > > Nice! Really good to see contention reduced, but in addition I'm a huge fan > of us removing the global state in vmalloc and this is a good start. > > I've noticed a small perf regression after 3 runs of ./test_vmalloc.sh > performance from an average of 119356136169 cycles to 120404645782 or +0.9% > but this doesn't seem especially egregious. > We are lack of extra vm_map_ram()/vm_unmap_ram() tests in the test_vmalloc.sh. It would be good to add them to the test-suite. > > 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. > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> > > --- > > mm/vmalloc.c | 50 ++++++++++++++++++++++++++------------------------ > > 1 file changed, 26 insertions(+), 24 deletions(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 978194dc2bb8..13b5342bed9a 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1911,6 +1911,7 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr) > > struct vmap_block_queue { > > spinlock_t lock; > > struct list_head free; > > + struct xarray vmap_blocks; > > }; > > > > struct vmap_block { > > @@ -1927,25 +1928,18 @@ struct vmap_block { > > /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */ > > 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. > > - */ > > Doesn't this comment still apply? Or is the idea of returning the "cookie" > not really viable? > Since a vmap_block_queue is a per-cpu thing, though it is not fully serialized in terms of per-cpu classical meaning, IMHO, it is not a big issue. If we return a cookie then, indeed, we do not need to find a vmap_block and performance wise it should be better. For how much, i do not know, it requires data. From the other hand an API has to be changed accordingly. But i can leave the comment! > > -static DEFINE_XARRAY(vmap_blocks); > > - > > -/* > > - * 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. > > - */ > > Again, is this comment no longer relevant? > Looks like yes :) But i am not sure i understand correctly what author meant. It looks like this: <snip> void *vm_map_ram(struct page **pages, unsigned int count, int node) { unsigned long size = (unsigned long)count << PAGE_SHIFT; unsigned long addr; void *mem; if (likely(count <= VMAP_MAX_ALLOC)) { mem = vb_alloc(size, GFP_KERNEL); if (IS_ERR(mem)) return NULL; ... <snip> instead of returning NULL, go directly with a fall-back, that is: <snip> struct vmap_area *va; va = alloc_vmap_area(size, PAGE_SIZE, VMALLOC_START, VMALLOC_END, node, GFP_KERNEL, VMAP_RAM); if (IS_ERR(va)) return NULL; addr = va->va_start; mem = (void *)addr; <snip> > > +static struct vmap_block_queue * > > +addr_to_vbq(unsigned long addr) > > +{ > > + int cpu = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > > + return &per_cpu(vmap_block_queue, cpu); > > +} > > Andrew's already commented on this, so I won't dwell but it does seem odd > to subdivide by number of possible CPUs rather than just use the actual > CPU. I guess your response to his question will also answer mine :) > I will upload a v2 where i try to explain in detail as much as i can, after that we can see if there are extra comments or questions and discuss if so. > > > > -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; > > + /* A start address of block an address belongs to. */ > > A nit, but might be worth referring to the assert in vmap_block_vaddr(), as > this comment seems a bit redundant otherwise as it is implied by the code > it comments. > OK. I can remove that comment. > > + return rounddown(addr, VMAP_BLOCK_SIZE); > > } > > > > static void *vmap_block_vaddr(unsigned long va_start, unsigned long pages_off) > > @@ -1953,7 +1947,7 @@ 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)); > > + BUG_ON(addr_to_vb_va_start(addr) != addr_to_vb_va_start(va_start)); > > Maybe nitty, but perhaps better to WARN_ON() here to avoid BUG_ON proliferation? > Indeed, it is better to go with WARN_ON() or even WARN_ON_ONCE(). > And can't this be the below? > > WARN_ON(addr_to_vb_va_start(addr) != va_start); > Yep, it can be. Thanks for it! > > return (void *)addr; > > } > > > > @@ -1970,7 +1964,6 @@ 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 +1996,8 @@ 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); > > This seems actually like a nice subtle improvement in that we are now > indexing always on va_start explicitly and will always load using > addr_to_vb_va_start(). > Yep, because we already have an index, it is a va->va_start. > > > if (err) { > > kfree(vb); > > free_vmap_area(va); > > @@ -2021,9 +2014,11 @@ 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 +2130,7 @@ 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 +2139,10 @@ 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 +3485,7 @@ 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 +3503,8 @@ 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 +4273,7 @@ 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 > >
diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 978194dc2bb8..13b5342bed9a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1911,6 +1911,7 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr) struct vmap_block_queue { spinlock_t lock; struct list_head free; + struct xarray vmap_blocks; }; struct vmap_block { @@ -1927,25 +1928,18 @@ struct vmap_block { /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */ 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. - */ -static DEFINE_XARRAY(vmap_blocks); - -/* - * 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. - */ +static struct vmap_block_queue * +addr_to_vbq(unsigned long addr) +{ + int cpu = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); + return &per_cpu(vmap_block_queue, cpu); +} -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; + /* A start address of block an address belongs to. */ + return rounddown(addr, VMAP_BLOCK_SIZE); } static void *vmap_block_vaddr(unsigned long va_start, unsigned long pages_off) @@ -1953,7 +1947,7 @@ 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)); + BUG_ON(addr_to_vb_va_start(addr) != addr_to_vb_va_start(va_start)); return (void *)addr; } @@ -1970,7 +1964,6 @@ 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 +1996,8 @@ 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); if (err) { kfree(vb); free_vmap_area(va); @@ -2021,9 +2014,11 @@ 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 +2130,7 @@ 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 +2139,10 @@ 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 +3485,7 @@ 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 +3503,8 @@ 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 +4273,7 @@ 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. */
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: <snip> ---------------------------------------- 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 ... <snip> 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. After this change the "xa_lock" can be considered as a noise in the same test condition: <snip> ... &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 ... <snip> 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. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> --- mm/vmalloc.c | 50 ++++++++++++++++++++++++++------------------------ 1 file changed, 26 insertions(+), 24 deletions(-)