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