From 5b82b703b69acc67b78b98a5efc897a3912719eb Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 25 Jan 2016 13:33:20 +0000 Subject: memory: RCU ram_list.dirty_memory[] for safe RAM hotplug Although accesses to ram_list.dirty_memory[] use atomics so multiple threads can safely dirty the bitmap, the data structure is not fully thread-safe yet. This patch handles the RAM hotplug case where ram_list.dirty_memory[] is grown. ram_list.dirty_memory[] is change from a regular bitmap to an RCU array of pointers to fixed-size bitmap blocks. Threads can continue accessing bitmap blocks while the array is being extended. See the comments in the code for an in-depth explanation of struct DirtyMemoryBlocks. I have tested that live migration with virtio-blk dataplane works. Signed-off-by: Stefan Hajnoczi Message-Id: <1453728801-5398-2-git-send-email-stefanha@redhat.com> Signed-off-by: Paolo Bonzini --- exec.c | 75 +++++++++++++++---- include/exec/ram_addr.h | 189 ++++++++++++++++++++++++++++++++++++++++++------ migration/ram.c | 4 - 3 files changed, 225 insertions(+), 43 deletions(-) diff --git a/exec.c b/exec.c index ab373604d7..7d67c11601 100644 --- a/exec.c +++ b/exec.c @@ -980,8 +980,9 @@ bool cpu_physical_memory_test_and_clear_dirty(ram_addr_t start, ram_addr_t length, unsigned client) { + DirtyMemoryBlocks *blocks; unsigned long end, page; - bool dirty; + bool dirty = false; if (length == 0) { return false; @@ -989,8 +990,22 @@ bool cpu_physical_memory_test_and_clear_dirty(ram_addr_t start, end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS; page = start >> TARGET_PAGE_BITS; - dirty = bitmap_test_and_clear_atomic(ram_list.dirty_memory[client], - page, end - page); + + rcu_read_lock(); + + blocks = atomic_rcu_read(&ram_list.dirty_memory[client]); + + while (page < end) { + unsigned long idx = page / DIRTY_MEMORY_BLOCK_SIZE; + unsigned long offset = page % DIRTY_MEMORY_BLOCK_SIZE; + unsigned long num = MIN(end - page, DIRTY_MEMORY_BLOCK_SIZE - offset); + + dirty |= bitmap_test_and_clear_atomic(blocks->blocks[idx], + offset, num); + page += num; + } + + rcu_read_unlock(); if (dirty && tcg_enabled()) { tlb_reset_dirty_range_all(start, length); @@ -1504,6 +1519,47 @@ int qemu_ram_resize(ram_addr_t base, ram_addr_t newsize, Error **errp) return 0; } +/* Called with ram_list.mutex held */ +static void dirty_memory_extend(ram_addr_t old_ram_size, + ram_addr_t new_ram_size) +{ + ram_addr_t old_num_blocks = DIV_ROUND_UP(old_ram_size, + DIRTY_MEMORY_BLOCK_SIZE); + ram_addr_t new_num_blocks = DIV_ROUND_UP(new_ram_size, + DIRTY_MEMORY_BLOCK_SIZE); + int i; + + /* Only need to extend if block count increased */ + if (new_num_blocks <= old_num_blocks) { + return; + } + + for (i = 0; i < DIRTY_MEMORY_NUM; i++) { + DirtyMemoryBlocks *old_blocks; + DirtyMemoryBlocks *new_blocks; + int j; + + old_blocks = atomic_rcu_read(&ram_list.dirty_memory[i]); + new_blocks = g_malloc(sizeof(*new_blocks) + + sizeof(new_blocks->blocks[0]) * new_num_blocks); + + if (old_num_blocks) { + memcpy(new_blocks->blocks, old_blocks->blocks, + old_num_blocks * sizeof(old_blocks->blocks[0])); + } + + for (j = old_num_blocks; j < new_num_blocks; j++) { + new_blocks->blocks[j] = bitmap_new(DIRTY_MEMORY_BLOCK_SIZE); + } + + atomic_rcu_set(&ram_list.dirty_memory[i], new_blocks); + + if (old_blocks) { + g_free_rcu(old_blocks, rcu); + } + } +} + static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp) { RAMBlock *block; @@ -1543,6 +1599,7 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp) (new_block->offset + new_block->max_length) >> TARGET_PAGE_BITS); if (new_ram_size > old_ram_size) { migration_bitmap_extend(old_ram_size, new_ram_size); + dirty_memory_extend(old_ram_size, new_ram_size); } /* Keep the list sorted from biggest to smallest block. Unlike QTAILQ, * QLIST (which has an RCU-friendly variant) does not have insertion at @@ -1568,18 +1625,6 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp) ram_list.version++; qemu_mutex_unlock_ramlist(); - new_ram_size = last_ram_offset() >> TARGET_PAGE_BITS; - - if (new_ram_size > old_ram_size) { - int i; - - /* ram_list.dirty_memory[] is protected by the iothread lock. */ - for (i = 0; i < DIRTY_MEMORY_NUM; i++) { - ram_list.dirty_memory[i] = - bitmap_zero_extend(ram_list.dirty_memory[i], - old_ram_size, new_ram_size); - } - } cpu_physical_memory_set_dirty_range(new_block->offset, new_block->used_length, DIRTY_CLIENTS_ALL); diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h index f2e872d87a..b1413a1286 100644 --- a/include/exec/ram_addr.h +++ b/include/exec/ram_addr.h @@ -49,13 +49,43 @@ static inline void *ramblock_ptr(RAMBlock *block, ram_addr_t offset) return (char *)block->host + offset; } +/* The dirty memory bitmap is split into fixed-size blocks to allow growth + * under RCU. The bitmap for a block can be accessed as follows: + * + * rcu_read_lock(); + * + * DirtyMemoryBlocks *blocks = + * atomic_rcu_read(&ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]); + * + * ram_addr_t idx = (addr >> TARGET_PAGE_BITS) / DIRTY_MEMORY_BLOCK_SIZE; + * unsigned long *block = blocks.blocks[idx]; + * ...access block bitmap... + * + * rcu_read_unlock(); + * + * Remember to check for the end of the block when accessing a range of + * addresses. Move on to the next block if you reach the end. + * + * Organization into blocks allows dirty memory to grow (but not shrink) under + * RCU. When adding new RAMBlocks requires the dirty memory to grow, a new + * DirtyMemoryBlocks array is allocated with pointers to existing blocks kept + * the same. Other threads can safely access existing blocks while dirty + * memory is being grown. When no threads are using the old DirtyMemoryBlocks + * anymore it is freed by RCU (but the underlying blocks stay because they are + * pointed to from the new DirtyMemoryBlocks). + */ +#define DIRTY_MEMORY_BLOCK_SIZE ((ram_addr_t)256 * 1024 * 8) +typedef struct { + struct rcu_head rcu; + unsigned long *blocks[]; +} DirtyMemoryBlocks; + typedef struct RAMList { QemuMutex mutex; - /* Protected by the iothread lock. */ - unsigned long *dirty_memory[DIRTY_MEMORY_NUM]; RAMBlock *mru_block; /* RCU-enabled, writes protected by the ramlist lock. */ QLIST_HEAD(, RAMBlock) blocks; + DirtyMemoryBlocks *dirty_memory[DIRTY_MEMORY_NUM]; uint32_t version; } RAMList; extern RAMList ram_list; @@ -89,30 +119,70 @@ static inline bool cpu_physical_memory_get_dirty(ram_addr_t start, ram_addr_t length, unsigned client) { - unsigned long end, page, next; + DirtyMemoryBlocks *blocks; + unsigned long end, page; + bool dirty = false; assert(client < DIRTY_MEMORY_NUM); end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS; page = start >> TARGET_PAGE_BITS; - next = find_next_bit(ram_list.dirty_memory[client], end, page); - return next < end; + rcu_read_lock(); + + blocks = atomic_rcu_read(&ram_list.dirty_memory[client]); + + while (page < end) { + unsigned long idx = page / DIRTY_MEMORY_BLOCK_SIZE; + unsigned long offset = page % DIRTY_MEMORY_BLOCK_SIZE; + unsigned long num = MIN(end - page, DIRTY_MEMORY_BLOCK_SIZE - offset); + + if (find_next_bit(blocks->blocks[idx], offset, num) < num) { + dirty = true; + break; + } + + page += num; + } + + rcu_read_unlock(); + + return dirty; } static inline bool cpu_physical_memory_all_dirty(ram_addr_t start, ram_addr_t length, unsigned client) { - unsigned long end, page, next; + DirtyMemoryBlocks *blocks; + unsigned long end, page; + bool dirty = true; assert(client < DIRTY_MEMORY_NUM); end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS; page = start >> TARGET_PAGE_BITS; - next = find_next_zero_bit(ram_list.dirty_memory[client], end, page); - return next >= end; + rcu_read_lock(); + + blocks = atomic_rcu_read(&ram_list.dirty_memory[client]); + + while (page < end) { + unsigned long idx = page / DIRTY_MEMORY_BLOCK_SIZE; + unsigned long offset = page % DIRTY_MEMORY_BLOCK_SIZE; + unsigned long num = MIN(end - page, DIRTY_MEMORY_BLOCK_SIZE - offset); + + if (find_next_zero_bit(blocks->blocks[idx], offset, num) < num) { + dirty = false; + break; + } + + page += num; + } + + rcu_read_unlock(); + + return dirty; } static inline bool cpu_physical_memory_get_dirty_flag(ram_addr_t addr, @@ -154,16 +224,31 @@ static inline uint8_t cpu_physical_memory_range_includes_clean(ram_addr_t start, static inline void cpu_physical_memory_set_dirty_flag(ram_addr_t addr, unsigned client) { + unsigned long page, idx, offset; + DirtyMemoryBlocks *blocks; + assert(client < DIRTY_MEMORY_NUM); - set_bit_atomic(addr >> TARGET_PAGE_BITS, ram_list.dirty_memory[client]); + + page = addr >> TARGET_PAGE_BITS; + idx = page / DIRTY_MEMORY_BLOCK_SIZE; + offset = page % DIRTY_MEMORY_BLOCK_SIZE; + + rcu_read_lock(); + + blocks = atomic_rcu_read(&ram_list.dirty_memory[client]); + + set_bit_atomic(offset, blocks->blocks[idx]); + + rcu_read_unlock(); } static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start, ram_addr_t length, uint8_t mask) { + DirtyMemoryBlocks *blocks[DIRTY_MEMORY_NUM]; unsigned long end, page; - unsigned long **d = ram_list.dirty_memory; + int i; if (!mask && !xen_enabled()) { return; @@ -171,15 +256,36 @@ static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start, end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS; page = start >> TARGET_PAGE_BITS; - if (likely(mask & (1 << DIRTY_MEMORY_MIGRATION))) { - bitmap_set_atomic(d[DIRTY_MEMORY_MIGRATION], page, end - page); - } - if (unlikely(mask & (1 << DIRTY_MEMORY_VGA))) { - bitmap_set_atomic(d[DIRTY_MEMORY_VGA], page, end - page); + + rcu_read_lock(); + + for (i = 0; i < DIRTY_MEMORY_NUM; i++) { + blocks[i] = atomic_rcu_read(&ram_list.dirty_memory[i]); } - if (unlikely(mask & (1 << DIRTY_MEMORY_CODE))) { - bitmap_set_atomic(d[DIRTY_MEMORY_CODE], page, end - page); + + while (page < end) { + unsigned long idx = page / DIRTY_MEMORY_BLOCK_SIZE; + unsigned long offset = page % DIRTY_MEMORY_BLOCK_SIZE; + unsigned long num = MIN(end - page, DIRTY_MEMORY_BLOCK_SIZE - offset); + + if (likely(mask & (1 << DIRTY_MEMORY_MIGRATION))) { + bitmap_set_atomic(blocks[DIRTY_MEMORY_MIGRATION]->blocks[idx], + offset, num); + } + if (unlikely(mask & (1 << DIRTY_MEMORY_VGA))) { + bitmap_set_atomic(blocks[DIRTY_MEMORY_VGA]->blocks[idx], + offset, num); + } + if (unlikely(mask & (1 << DIRTY_MEMORY_CODE))) { + bitmap_set_atomic(blocks[DIRTY_MEMORY_CODE]->blocks[idx], + offset, num); + } + + page += num; } + + rcu_read_unlock(); + xen_modified_memory(start, length); } @@ -199,21 +305,41 @@ static inline void cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap, /* start address is aligned at the start of a word? */ if ((((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) && (hpratio == 1)) { + unsigned long **blocks[DIRTY_MEMORY_NUM]; + unsigned long idx; + unsigned long offset; long k; long nr = BITS_TO_LONGS(pages); + idx = (start >> TARGET_PAGE_BITS) / DIRTY_MEMORY_BLOCK_SIZE; + offset = BIT_WORD((start >> TARGET_PAGE_BITS) % + DIRTY_MEMORY_BLOCK_SIZE); + + rcu_read_lock(); + + for (i = 0; i < DIRTY_MEMORY_NUM; i++) { + blocks[i] = atomic_rcu_read(&ram_list.dirty_memory[i])->blocks; + } + for (k = 0; k < nr; k++) { if (bitmap[k]) { unsigned long temp = leul_to_cpu(bitmap[k]); - unsigned long **d = ram_list.dirty_memory; - atomic_or(&d[DIRTY_MEMORY_MIGRATION][page + k], temp); - atomic_or(&d[DIRTY_MEMORY_VGA][page + k], temp); + atomic_or(&blocks[DIRTY_MEMORY_MIGRATION][idx][offset], temp); + atomic_or(&blocks[DIRTY_MEMORY_VGA][idx][offset], temp); if (tcg_enabled()) { - atomic_or(&d[DIRTY_MEMORY_CODE][page + k], temp); + atomic_or(&blocks[DIRTY_MEMORY_CODE][idx][offset], temp); } } + + if (++offset >= BITS_TO_LONGS(DIRTY_MEMORY_BLOCK_SIZE)) { + offset = 0; + idx++; + } } + + rcu_read_unlock(); + xen_modified_memory(start, pages << TARGET_PAGE_BITS); } else { uint8_t clients = tcg_enabled() ? DIRTY_CLIENTS_ALL : DIRTY_CLIENTS_NOCODE; @@ -265,18 +391,33 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(unsigned long *dest, if (((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) { int k; int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS); - unsigned long *src = ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]; + unsigned long * const *src; + unsigned long idx = (page * BITS_PER_LONG) / DIRTY_MEMORY_BLOCK_SIZE; + unsigned long offset = BIT_WORD((page * BITS_PER_LONG) % + DIRTY_MEMORY_BLOCK_SIZE); + + rcu_read_lock(); + + src = atomic_rcu_read( + &ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION])->blocks; for (k = page; k < page + nr; k++) { - if (src[k]) { - unsigned long bits = atomic_xchg(&src[k], 0); + if (src[idx][offset]) { + unsigned long bits = atomic_xchg(&src[idx][offset], 0); unsigned long new_dirty; new_dirty = ~dest[k]; dest[k] |= bits; new_dirty &= bits; num_dirty += ctpopl(new_dirty); } + + if (++offset >= BITS_TO_LONGS(DIRTY_MEMORY_BLOCK_SIZE)) { + offset = 0; + idx++; + } } + + rcu_read_unlock(); } else { for (addr = 0; addr < length; addr += TARGET_PAGE_SIZE) { if (cpu_physical_memory_test_and_clear_dirty( diff --git a/migration/ram.c b/migration/ram.c index 3cdfea4a5c..96c749face 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -609,7 +609,6 @@ static void migration_bitmap_sync_init(void) iterations_prev = 0; } -/* Called with iothread lock held, to protect ram_list.dirty_memory[] */ static void migration_bitmap_sync(void) { RAMBlock *block; @@ -1921,8 +1920,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque) acct_clear(); } - /* iothread lock needed for ram_list.dirty_memory[] */ - qemu_mutex_lock_iothread(); qemu_mutex_lock_ramlist(); rcu_read_lock(); bytes_transferred = 0; @@ -1947,7 +1944,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque) memory_global_dirty_log_start(); migration_bitmap_sync(); qemu_mutex_unlock_ramlist(); - qemu_mutex_unlock_iothread(); qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE); -- cgit v1.2.3