1 /* 2 * Request reply cache. This is currently a global cache, but this may 3 * change in the future and be a per-client cache. 4 * 5 * This code is heavily inspired by the 44BSD implementation, although 6 * it does things a bit differently. 7 * 8 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de> 9 */ 10 11 #include <linux/slab.h> 12 #include <linux/sunrpc/addr.h> 13 #include <linux/highmem.h> 14 #include <linux/log2.h> 15 #include <linux/hash.h> 16 #include <net/checksum.h> 17 18 #include "nfsd.h" 19 #include "cache.h" 20 21 #define NFSDDBG_FACILITY NFSDDBG_REPCACHE 22 23 /* 24 * We use this value to determine the number of hash buckets from the max 25 * cache size, the idea being that when the cache is at its maximum number 26 * of entries, then this should be the average number of entries per bucket. 27 */ 28 #define TARGET_BUCKET_SIZE 64 29 30 struct nfsd_drc_bucket { 31 struct list_head lru_head; 32 spinlock_t cache_lock; 33 }; 34 35 static struct nfsd_drc_bucket *drc_hashtbl; 36 static struct kmem_cache *drc_slab; 37 38 /* max number of entries allowed in the cache */ 39 static unsigned int max_drc_entries; 40 41 /* number of significant bits in the hash value */ 42 static unsigned int maskbits; 43 static unsigned int drc_hashsize; 44 45 /* 46 * Stats and other tracking of on the duplicate reply cache. All of these and 47 * the "rc" fields in nfsdstats are protected by the cache_lock 48 */ 49 50 /* total number of entries */ 51 static atomic_t num_drc_entries; 52 53 /* cache misses due only to checksum comparison failures */ 54 static unsigned int payload_misses; 55 56 /* amount of memory (in bytes) currently consumed by the DRC */ 57 static unsigned int drc_mem_usage; 58 59 /* longest hash chain seen */ 60 static unsigned int longest_chain; 61 62 /* size of cache when we saw the longest hash chain */ 63 static unsigned int longest_chain_cachesize; 64 65 static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec); 66 static void cache_cleaner_func(struct work_struct *unused); 67 static unsigned long nfsd_reply_cache_count(struct shrinker *shrink, 68 struct shrink_control *sc); 69 static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink, 70 struct shrink_control *sc); 71 72 static struct shrinker nfsd_reply_cache_shrinker = { 73 .scan_objects = nfsd_reply_cache_scan, 74 .count_objects = nfsd_reply_cache_count, 75 .seeks = 1, 76 }; 77 78 /* 79 * locking for the reply cache: 80 * A cache entry is "single use" if c_state == RC_INPROG 81 * Otherwise, it when accessing _prev or _next, the lock must be held. 82 */ 83 static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func); 84 85 /* 86 * Put a cap on the size of the DRC based on the amount of available 87 * low memory in the machine. 88 * 89 * 64MB: 8192 90 * 128MB: 11585 91 * 256MB: 16384 92 * 512MB: 23170 93 * 1GB: 32768 94 * 2GB: 46340 95 * 4GB: 65536 96 * 8GB: 92681 97 * 16GB: 131072 98 * 99 * ...with a hard cap of 256k entries. In the worst case, each entry will be 100 * ~1k, so the above numbers should give a rough max of the amount of memory 101 * used in k. 102 */ 103 static unsigned int 104 nfsd_cache_size_limit(void) 105 { 106 unsigned int limit; 107 unsigned long low_pages = totalram_pages - totalhigh_pages; 108 109 limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10); 110 return min_t(unsigned int, limit, 256*1024); 111 } 112 113 /* 114 * Compute the number of hash buckets we need. Divide the max cachesize by 115 * the "target" max bucket size, and round up to next power of two. 116 */ 117 static unsigned int 118 nfsd_hashsize(unsigned int limit) 119 { 120 return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE); 121 } 122 123 static u32 124 nfsd_cache_hash(__be32 xid) 125 { 126 return hash_32(be32_to_cpu(xid), maskbits); 127 } 128 129 static struct svc_cacherep * 130 nfsd_reply_cache_alloc(void) 131 { 132 struct svc_cacherep *rp; 133 134 rp = kmem_cache_alloc(drc_slab, GFP_KERNEL); 135 if (rp) { 136 rp->c_state = RC_UNUSED; 137 rp->c_type = RC_NOCACHE; 138 INIT_LIST_HEAD(&rp->c_lru); 139 } 140 return rp; 141 } 142 143 static void 144 nfsd_reply_cache_free_locked(struct svc_cacherep *rp) 145 { 146 if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) { 147 drc_mem_usage -= rp->c_replvec.iov_len; 148 kfree(rp->c_replvec.iov_base); 149 } 150 list_del(&rp->c_lru); 151 atomic_dec(&num_drc_entries); 152 drc_mem_usage -= sizeof(*rp); 153 kmem_cache_free(drc_slab, rp); 154 } 155 156 static void 157 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp) 158 { 159 spin_lock(&b->cache_lock); 160 nfsd_reply_cache_free_locked(rp); 161 spin_unlock(&b->cache_lock); 162 } 163 164 int nfsd_reply_cache_init(void) 165 { 166 unsigned int hashsize; 167 unsigned int i; 168 169 max_drc_entries = nfsd_cache_size_limit(); 170 atomic_set(&num_drc_entries, 0); 171 hashsize = nfsd_hashsize(max_drc_entries); 172 maskbits = ilog2(hashsize); 173 174 register_shrinker(&nfsd_reply_cache_shrinker); 175 drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep), 176 0, 0, NULL); 177 if (!drc_slab) 178 goto out_nomem; 179 180 drc_hashtbl = kcalloc(hashsize, sizeof(*drc_hashtbl), GFP_KERNEL); 181 if (!drc_hashtbl) 182 goto out_nomem; 183 for (i = 0; i < hashsize; i++) { 184 INIT_LIST_HEAD(&drc_hashtbl[i].lru_head); 185 spin_lock_init(&drc_hashtbl[i].cache_lock); 186 } 187 drc_hashsize = hashsize; 188 189 return 0; 190 out_nomem: 191 printk(KERN_ERR "nfsd: failed to allocate reply cache\n"); 192 nfsd_reply_cache_shutdown(); 193 return -ENOMEM; 194 } 195 196 void nfsd_reply_cache_shutdown(void) 197 { 198 struct svc_cacherep *rp; 199 unsigned int i; 200 201 unregister_shrinker(&nfsd_reply_cache_shrinker); 202 cancel_delayed_work_sync(&cache_cleaner); 203 204 for (i = 0; i < drc_hashsize; i++) { 205 struct list_head *head = &drc_hashtbl[i].lru_head; 206 while (!list_empty(head)) { 207 rp = list_first_entry(head, struct svc_cacherep, c_lru); 208 nfsd_reply_cache_free_locked(rp); 209 } 210 } 211 212 kfree (drc_hashtbl); 213 drc_hashtbl = NULL; 214 drc_hashsize = 0; 215 216 if (drc_slab) { 217 kmem_cache_destroy(drc_slab); 218 drc_slab = NULL; 219 } 220 } 221 222 /* 223 * Move cache entry to end of LRU list, and queue the cleaner to run if it's 224 * not already scheduled. 225 */ 226 static void 227 lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp) 228 { 229 rp->c_timestamp = jiffies; 230 list_move_tail(&rp->c_lru, &b->lru_head); 231 schedule_delayed_work(&cache_cleaner, RC_EXPIRE); 232 } 233 234 static long 235 prune_bucket(struct nfsd_drc_bucket *b) 236 { 237 struct svc_cacherep *rp, *tmp; 238 long freed = 0; 239 240 list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) { 241 /* 242 * Don't free entries attached to calls that are still 243 * in-progress, but do keep scanning the list. 244 */ 245 if (rp->c_state == RC_INPROG) 246 continue; 247 if (atomic_read(&num_drc_entries) <= max_drc_entries && 248 time_before(jiffies, rp->c_timestamp + RC_EXPIRE)) 249 break; 250 nfsd_reply_cache_free_locked(rp); 251 freed++; 252 } 253 return freed; 254 } 255 256 /* 257 * Walk the LRU list and prune off entries that are older than RC_EXPIRE. 258 * Also prune the oldest ones when the total exceeds the max number of entries. 259 */ 260 static long 261 prune_cache_entries(void) 262 { 263 unsigned int i; 264 long freed = 0; 265 bool cancel = true; 266 267 for (i = 0; i < drc_hashsize; i++) { 268 struct nfsd_drc_bucket *b = &drc_hashtbl[i]; 269 270 if (list_empty(&b->lru_head)) 271 continue; 272 spin_lock(&b->cache_lock); 273 freed += prune_bucket(b); 274 if (!list_empty(&b->lru_head)) 275 cancel = false; 276 spin_unlock(&b->cache_lock); 277 } 278 279 /* 280 * Conditionally rearm the job to run in RC_EXPIRE since we just 281 * ran the pruner. 282 */ 283 if (!cancel) 284 mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE); 285 return freed; 286 } 287 288 static void 289 cache_cleaner_func(struct work_struct *unused) 290 { 291 prune_cache_entries(); 292 } 293 294 static unsigned long 295 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc) 296 { 297 return atomic_read(&num_drc_entries); 298 } 299 300 static unsigned long 301 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc) 302 { 303 return prune_cache_entries(); 304 } 305 /* 306 * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes 307 */ 308 static __wsum 309 nfsd_cache_csum(struct svc_rqst *rqstp) 310 { 311 int idx; 312 unsigned int base; 313 __wsum csum; 314 struct xdr_buf *buf = &rqstp->rq_arg; 315 const unsigned char *p = buf->head[0].iov_base; 316 size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len, 317 RC_CSUMLEN); 318 size_t len = min(buf->head[0].iov_len, csum_len); 319 320 /* rq_arg.head first */ 321 csum = csum_partial(p, len, 0); 322 csum_len -= len; 323 324 /* Continue into page array */ 325 idx = buf->page_base / PAGE_SIZE; 326 base = buf->page_base & ~PAGE_MASK; 327 while (csum_len) { 328 p = page_address(buf->pages[idx]) + base; 329 len = min_t(size_t, PAGE_SIZE - base, csum_len); 330 csum = csum_partial(p, len, csum); 331 csum_len -= len; 332 base = 0; 333 ++idx; 334 } 335 return csum; 336 } 337 338 static bool 339 nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp) 340 { 341 /* Check RPC XID first */ 342 if (rqstp->rq_xid != rp->c_xid) 343 return false; 344 /* compare checksum of NFS data */ 345 if (csum != rp->c_csum) { 346 ++payload_misses; 347 return false; 348 } 349 350 /* Other discriminators */ 351 if (rqstp->rq_proc != rp->c_proc || 352 rqstp->rq_prot != rp->c_prot || 353 rqstp->rq_vers != rp->c_vers || 354 rqstp->rq_arg.len != rp->c_len || 355 !rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) || 356 rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr)) 357 return false; 358 359 return true; 360 } 361 362 /* 363 * Search the request hash for an entry that matches the given rqstp. 364 * Must be called with cache_lock held. Returns the found entry or 365 * NULL on failure. 366 */ 367 static struct svc_cacherep * 368 nfsd_cache_search(struct nfsd_drc_bucket *b, struct svc_rqst *rqstp, 369 __wsum csum) 370 { 371 struct svc_cacherep *rp, *ret = NULL; 372 struct list_head *rh = &b->lru_head; 373 unsigned int entries = 0; 374 375 list_for_each_entry(rp, rh, c_lru) { 376 ++entries; 377 if (nfsd_cache_match(rqstp, csum, rp)) { 378 ret = rp; 379 break; 380 } 381 } 382 383 /* tally hash chain length stats */ 384 if (entries > longest_chain) { 385 longest_chain = entries; 386 longest_chain_cachesize = atomic_read(&num_drc_entries); 387 } else if (entries == longest_chain) { 388 /* prefer to keep the smallest cachesize possible here */ 389 longest_chain_cachesize = min_t(unsigned int, 390 longest_chain_cachesize, 391 atomic_read(&num_drc_entries)); 392 } 393 394 return ret; 395 } 396 397 /* 398 * Try to find an entry matching the current call in the cache. When none 399 * is found, we try to grab the oldest expired entry off the LRU list. If 400 * a suitable one isn't there, then drop the cache_lock and allocate a 401 * new one, then search again in case one got inserted while this thread 402 * didn't hold the lock. 403 */ 404 int 405 nfsd_cache_lookup(struct svc_rqst *rqstp) 406 { 407 struct svc_cacherep *rp, *found; 408 __be32 xid = rqstp->rq_xid; 409 u32 proto = rqstp->rq_prot, 410 vers = rqstp->rq_vers, 411 proc = rqstp->rq_proc; 412 __wsum csum; 413 u32 hash = nfsd_cache_hash(xid); 414 struct nfsd_drc_bucket *b = &drc_hashtbl[hash]; 415 unsigned long age; 416 int type = rqstp->rq_cachetype; 417 int rtn = RC_DOIT; 418 419 rqstp->rq_cacherep = NULL; 420 if (type == RC_NOCACHE) { 421 nfsdstats.rcnocache++; 422 return rtn; 423 } 424 425 csum = nfsd_cache_csum(rqstp); 426 427 /* 428 * Since the common case is a cache miss followed by an insert, 429 * preallocate an entry. 430 */ 431 rp = nfsd_reply_cache_alloc(); 432 spin_lock(&b->cache_lock); 433 if (likely(rp)) { 434 atomic_inc(&num_drc_entries); 435 drc_mem_usage += sizeof(*rp); 436 } 437 438 /* go ahead and prune the cache */ 439 prune_bucket(b); 440 441 found = nfsd_cache_search(b, rqstp, csum); 442 if (found) { 443 if (likely(rp)) 444 nfsd_reply_cache_free_locked(rp); 445 rp = found; 446 goto found_entry; 447 } 448 449 if (!rp) { 450 dprintk("nfsd: unable to allocate DRC entry!\n"); 451 goto out; 452 } 453 454 nfsdstats.rcmisses++; 455 rqstp->rq_cacherep = rp; 456 rp->c_state = RC_INPROG; 457 rp->c_xid = xid; 458 rp->c_proc = proc; 459 rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp)); 460 rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp))); 461 rp->c_prot = proto; 462 rp->c_vers = vers; 463 rp->c_len = rqstp->rq_arg.len; 464 rp->c_csum = csum; 465 466 lru_put_end(b, rp); 467 468 /* release any buffer */ 469 if (rp->c_type == RC_REPLBUFF) { 470 drc_mem_usage -= rp->c_replvec.iov_len; 471 kfree(rp->c_replvec.iov_base); 472 rp->c_replvec.iov_base = NULL; 473 } 474 rp->c_type = RC_NOCACHE; 475 out: 476 spin_unlock(&b->cache_lock); 477 return rtn; 478 479 found_entry: 480 nfsdstats.rchits++; 481 /* We found a matching entry which is either in progress or done. */ 482 age = jiffies - rp->c_timestamp; 483 lru_put_end(b, rp); 484 485 rtn = RC_DROPIT; 486 /* Request being processed or excessive rexmits */ 487 if (rp->c_state == RC_INPROG || age < RC_DELAY) 488 goto out; 489 490 /* From the hall of fame of impractical attacks: 491 * Is this a user who tries to snoop on the cache? */ 492 rtn = RC_DOIT; 493 if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure) 494 goto out; 495 496 /* Compose RPC reply header */ 497 switch (rp->c_type) { 498 case RC_NOCACHE: 499 break; 500 case RC_REPLSTAT: 501 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat); 502 rtn = RC_REPLY; 503 break; 504 case RC_REPLBUFF: 505 if (!nfsd_cache_append(rqstp, &rp->c_replvec)) 506 goto out; /* should not happen */ 507 rtn = RC_REPLY; 508 break; 509 default: 510 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type); 511 nfsd_reply_cache_free_locked(rp); 512 } 513 514 goto out; 515 } 516 517 /* 518 * Update a cache entry. This is called from nfsd_dispatch when 519 * the procedure has been executed and the complete reply is in 520 * rqstp->rq_res. 521 * 522 * We're copying around data here rather than swapping buffers because 523 * the toplevel loop requires max-sized buffers, which would be a waste 524 * of memory for a cache with a max reply size of 100 bytes (diropokres). 525 * 526 * If we should start to use different types of cache entries tailored 527 * specifically for attrstat and fh's, we may save even more space. 528 * 529 * Also note that a cachetype of RC_NOCACHE can legally be passed when 530 * nfsd failed to encode a reply that otherwise would have been cached. 531 * In this case, nfsd_cache_update is called with statp == NULL. 532 */ 533 void 534 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp) 535 { 536 struct svc_cacherep *rp = rqstp->rq_cacherep; 537 struct kvec *resv = &rqstp->rq_res.head[0], *cachv; 538 u32 hash; 539 struct nfsd_drc_bucket *b; 540 int len; 541 size_t bufsize = 0; 542 543 if (!rp) 544 return; 545 546 hash = nfsd_cache_hash(rp->c_xid); 547 b = &drc_hashtbl[hash]; 548 549 len = resv->iov_len - ((char*)statp - (char*)resv->iov_base); 550 len >>= 2; 551 552 /* Don't cache excessive amounts of data and XDR failures */ 553 if (!statp || len > (256 >> 2)) { 554 nfsd_reply_cache_free(b, rp); 555 return; 556 } 557 558 switch (cachetype) { 559 case RC_REPLSTAT: 560 if (len != 1) 561 printk("nfsd: RC_REPLSTAT/reply len %d!\n",len); 562 rp->c_replstat = *statp; 563 break; 564 case RC_REPLBUFF: 565 cachv = &rp->c_replvec; 566 bufsize = len << 2; 567 cachv->iov_base = kmalloc(bufsize, GFP_KERNEL); 568 if (!cachv->iov_base) { 569 nfsd_reply_cache_free(b, rp); 570 return; 571 } 572 cachv->iov_len = bufsize; 573 memcpy(cachv->iov_base, statp, bufsize); 574 break; 575 case RC_NOCACHE: 576 nfsd_reply_cache_free(b, rp); 577 return; 578 } 579 spin_lock(&b->cache_lock); 580 drc_mem_usage += bufsize; 581 lru_put_end(b, rp); 582 rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags); 583 rp->c_type = cachetype; 584 rp->c_state = RC_DONE; 585 spin_unlock(&b->cache_lock); 586 return; 587 } 588 589 /* 590 * Copy cached reply to current reply buffer. Should always fit. 591 * FIXME as reply is in a page, we should just attach the page, and 592 * keep a refcount.... 593 */ 594 static int 595 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data) 596 { 597 struct kvec *vec = &rqstp->rq_res.head[0]; 598 599 if (vec->iov_len + data->iov_len > PAGE_SIZE) { 600 printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n", 601 data->iov_len); 602 return 0; 603 } 604 memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len); 605 vec->iov_len += data->iov_len; 606 return 1; 607 } 608 609 /* 610 * Note that fields may be added, removed or reordered in the future. Programs 611 * scraping this file for info should test the labels to ensure they're 612 * getting the correct field. 613 */ 614 static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v) 615 { 616 seq_printf(m, "max entries: %u\n", max_drc_entries); 617 seq_printf(m, "num entries: %u\n", 618 atomic_read(&num_drc_entries)); 619 seq_printf(m, "hash buckets: %u\n", 1 << maskbits); 620 seq_printf(m, "mem usage: %u\n", drc_mem_usage); 621 seq_printf(m, "cache hits: %u\n", nfsdstats.rchits); 622 seq_printf(m, "cache misses: %u\n", nfsdstats.rcmisses); 623 seq_printf(m, "not cached: %u\n", nfsdstats.rcnocache); 624 seq_printf(m, "payload misses: %u\n", payload_misses); 625 seq_printf(m, "longest chain len: %u\n", longest_chain); 626 seq_printf(m, "cachesize at longest: %u\n", longest_chain_cachesize); 627 return 0; 628 } 629 630 int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file) 631 { 632 return single_open(file, nfsd_reply_cache_stats_show, NULL); 633 } 634