From: Darrick J. Wong <djwong@xxxxxxxxxx> Use a hash to avoid the linear scan. Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx> --- lib/ext2fs/unix_io.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 80 insertions(+), 1 deletion(-) diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c index f8be1fe6f8d2c0..7078f3e2e30175 100644 --- a/lib/ext2fs/unix_io.c +++ b/lib/ext2fs/unix_io.c @@ -75,6 +75,40 @@ #include "ext2fs.h" #include "ext2fsP.h" +static inline int fls(int x) +{ + int r = 32; + + if (!x) + return 0; + if (!(x & 0xffff0000u)) { + x = (x & 0xffffu) << 16; + r -= 16; + } + if (!(x & 0xff000000u)) { + x = (x & 0xffffffu) << 8; + r -= 8; + } + if (!(x & 0xf0000000u)) { + x = (x & 0xfffffffu) << 4; + r -= 4; + } + if (!(x & 0xc0000000u)) { + x = (x & 0x3fffffffu) << 2; + r -= 2; + } + if (!(x & 0x80000000u)) { + r -= 1; + } + return r; +} + +/* Get high bit set out of 32-bit argument, -1 if none set */ +static inline int highbit32(uint32_t v) +{ + return fls(v) - 1; +} + /* * For checking structure magic numbers... */ @@ -104,6 +138,7 @@ struct unix_private_data { ext2_loff_t offset; struct unix_cache *cache; unsigned int cache_size; + unsigned int cache_hash_shift; void *bounce; struct struct_io_stats io_stats; #ifdef HAVE_PTHREAD @@ -516,6 +551,27 @@ static void free_cache(struct unix_private_data *data) } #ifndef NO_IO_CACHE + +/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */ +#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL +#define CACHE_LINE_SIZE 64 + +/* buffer cache hashing function, crudely stolen from xfsprogs */ +unsigned int +cache_hash(struct unix_private_data *data, blk64_t blkno) +{ + uint64_t hashval = blkno; + uint64_t tmp; + + /* the default cache size is small, just do a linear scan */ + if (data->cache_size <= DEFAULT_CACHE_SIZE) + return 0; + + tmp = hashval ^ (GOLDEN_RATIO_PRIME + hashval) / CACHE_LINE_SIZE; + tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> data->cache_hash_shift); + return tmp % data->cache_size; +} + /* * Try to find a block in the cache. If the block is not found, and * eldest is a non-zero pointer, then fill in eldest with the cache @@ -526,10 +582,30 @@ static struct unix_cache *find_cached_block(struct unix_private_data *data, struct unix_cache **eldest) { struct unix_cache *cache, *unused_cache, *oldest_cache; + unsigned int hash = cache_hash(data, block); int i; unused_cache = oldest_cache = 0; - for (i=0, cache = data->cache; i < data->cache_size; i++, cache++) { + /* walk [hash..] cache elements */ + for (i = hash, cache = data->cache + hash; + i < data->cache_size; + i++, cache++) { + if (!cache->in_use) { + if (!unused_cache) + unused_cache = cache; + continue; + } + if (cache->block == block) { + cache->access_time = ++data->access_time; + data->io_stats.cache_hits++; + return cache; + } + if (!oldest_cache || + (cache->access_time < oldest_cache->access_time)) + oldest_cache = cache; + } + /* walk [..hash] since we didnt find a good slot yet */ + for (i = 0, cache = data->cache; i < hash; i++, cache++) { if (!cache->in_use) { if (!unused_cache) unused_cache = cache; @@ -685,6 +761,7 @@ static errcode_t shrink_cache(io_channel channel, data->cache = new_cache; data->cache_size = new_size; + data->cache_hash_shift = highbit32(data->cache_size); unlock: mutex_unlock(data, CACHE_MTX); @@ -727,6 +804,7 @@ static errcode_t grow_cache(io_channel channel, data->cache = new_cache; data->cache_size = new_size; + data->cache_hash_shift = highbit32(data->cache_size); unlock: mutex_unlock(data, CACHE_MTX); @@ -828,6 +906,7 @@ static errcode_t unix_open_channel(const char *name, int fd, data->dev = fd; data->cache_size = DEFAULT_CACHE_SIZE; + data->cache_hash_shift = highbit32(data->cache_size); data->cache = calloc(DEFAULT_CACHE_SIZE, sizeof(struct unix_cache)); if (!data->cache) { retval = EXT2_ET_NO_MEMORY;