fs/nfsd/nfscache.c

   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         int status = 0;
 169
 170         max_drc_entries = nfsd_cache_size_limit();
 171         atomic_set(&num_drc_entries, 0);
 172         hashsize = nfsd_hashsize(max_drc_entries);
 173         maskbits = ilog2(hashsize);
 174
 175         status = register_shrinker(&nfsd_reply_cache_shrinker);
 176         if (status)
 177                 return status;
 178
 179         drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
 180                                         0, 0, NULL);
 181         if (!drc_slab)
 182                 goto out_nomem;
 183
 184         drc_hashtbl = kcalloc(hashsize, sizeof(*drc_hashtbl), GFP_KERNEL);
 185         if (!drc_hashtbl)
 186                 goto out_nomem;
 187         for (i = 0; i < hashsize; i++) {
 188                 INIT_LIST_HEAD(&drc_hashtbl[i].lru_head);
 189                 spin_lock_init(&drc_hashtbl[i].cache_lock);
 190         }
 191         drc_hashsize = hashsize;
 192
 193         return 0;
 194 out_nomem:
 195         printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 196         nfsd_reply_cache_shutdown();
 197         return -ENOMEM;
 198 }
 199
 200 void nfsd_reply_cache_shutdown(void)
 201 {
 202         struct svc_cacherep     *rp;
 203         unsigned int i;
 204
 205         unregister_shrinker(&nfsd_reply_cache_shrinker);
 206         cancel_delayed_work_sync(&cache_cleaner);
 207
 208         for (i = 0; i < drc_hashsize; i++) {
 209                 struct list_head *head = &drc_hashtbl[i].lru_head;
 210                 while (!list_empty(head)) {
 211                         rp = list_first_entry(head, struct svc_cacherep, c_lru);
 212                         nfsd_reply_cache_free_locked(rp);
 213                 }
 214         }
 215
 216         kfree (drc_hashtbl);
 217         drc_hashtbl = NULL;
 218         drc_hashsize = 0;
 219
 220         if (drc_slab) {
 221                 kmem_cache_destroy(drc_slab);
 222                 drc_slab = NULL;
 223         }
 224 }
 225
 226 /*
 227  * Move cache entry to end of LRU list, and queue the cleaner to run if it's
 228  * not already scheduled.
 229  */
 230 static void
 231 lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
 232 {
 233         rp->c_timestamp = jiffies;
 234         list_move_tail(&rp->c_lru, &b->lru_head);
 235         schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
 236 }
 237
 238 static long
 239 prune_bucket(struct nfsd_drc_bucket *b)
 240 {
 241         struct svc_cacherep *rp, *tmp;
 242         long freed = 0;
 243
 244         list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
 245                 /*
 246                  * Don't free entries attached to calls that are still
 247                  * in-progress, but do keep scanning the list.
 248                  */
 249                 if (rp->c_state == RC_INPROG)
 250                         continue;
 251                 if (atomic_read(&num_drc_entries) <= max_drc_entries &&
 252                     time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
 253                         break;
 254                 nfsd_reply_cache_free_locked(rp);
 255                 freed++;
 256         }
 257         return freed;
 258 }
 259
 260 /*
 261  * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
 262  * Also prune the oldest ones when the total exceeds the max number of entries.
 263  */
 264 static long
 265 prune_cache_entries(void)
 266 {
 267         unsigned int i;
 268         long freed = 0;
 269         bool cancel = true;
 270
 271         for (i = 0; i < drc_hashsize; i++) {
 272                 struct nfsd_drc_bucket *b = &drc_hashtbl[i];
 273
 274                 if (list_empty(&b->lru_head))
 275                         continue;
 276                 spin_lock(&b->cache_lock);
 277                 freed += prune_bucket(b);
 278                 if (!list_empty(&b->lru_head))
 279                         cancel = false;
 280                 spin_unlock(&b->cache_lock);
 281         }
 282
 283         /*
 284          * Conditionally rearm the job to run in RC_EXPIRE since we just
 285          * ran the pruner.
 286          */
 287         if (!cancel)
 288                 mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
 289         return freed;
 290 }
 291
 292 static void
 293 cache_cleaner_func(struct work_struct *unused)
 294 {
 295         prune_cache_entries();
 296 }
 297
 298 static unsigned long
 299 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 300 {
 301         return atomic_read(&num_drc_entries);
 302 }
 303
 304 static unsigned long
 305 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
 306 {
 307         return prune_cache_entries();
 308 }
 309 /*
 310  * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
 311  */
 312 static __wsum
 313 nfsd_cache_csum(struct svc_rqst *rqstp)
 314 {
 315         int idx;
 316         unsigned int base;
 317         __wsum csum;
 318         struct xdr_buf *buf = &rqstp->rq_arg;
 319         const unsigned char *p = buf->head[0].iov_base;
 320         size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
 321                                 RC_CSUMLEN);
 322         size_t len = min(buf->head[0].iov_len, csum_len);
 323
 324         /* rq_arg.head first */
 325         csum = csum_partial(p, len, 0);
 326         csum_len -= len;
 327
 328         /* Continue into page array */
 329         idx = buf->page_base / PAGE_SIZE;
 330         base = buf->page_base & ~PAGE_MASK;
 331         while (csum_len) {
 332                 p = page_address(buf->pages[idx]) + base;
 333                 len = min_t(size_t, PAGE_SIZE - base, csum_len);
 334                 csum = csum_partial(p, len, csum);
 335                 csum_len -= len;
 336                 base = 0;
 337                 ++idx;
 338         }
 339         return csum;
 340 }
 341
 342 static bool
 343 nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp)
 344 {
 345         /* Check RPC XID first */
 346         if (rqstp->rq_xid != rp->c_xid)
 347                 return false;
 348         /* compare checksum of NFS data */
 349         if (csum != rp->c_csum) {
 350                 ++payload_misses;
 351                 return false;
 352         }
 353
 354         /* Other discriminators */
 355         if (rqstp->rq_proc != rp->c_proc ||
 356             rqstp->rq_prot != rp->c_prot ||
 357             rqstp->rq_vers != rp->c_vers ||
 358             rqstp->rq_arg.len != rp->c_len ||
 359             !rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) ||
 360             rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr))
 361                 return false;
 362
 363         return true;
 364 }
 365
 366 /*
 367  * Search the request hash for an entry that matches the given rqstp.
 368  * Must be called with cache_lock held. Returns the found entry or
 369  * NULL on failure.
 370  */
 371 static struct svc_cacherep *
 372 nfsd_cache_search(struct nfsd_drc_bucket *b, struct svc_rqst *rqstp,
 373                 __wsum csum)
 374 {
 375         struct svc_cacherep     *rp, *ret = NULL;
 376         struct list_head        *rh = &b->lru_head;
 377         unsigned int            entries = 0;
 378
 379         list_for_each_entry(rp, rh, c_lru) {
 380                 ++entries;
 381                 if (nfsd_cache_match(rqstp, csum, rp)) {
 382                         ret = rp;
 383                         break;
 384                 }
 385         }
 386
 387         /* tally hash chain length stats */
 388         if (entries > longest_chain) {
 389                 longest_chain = entries;
 390                 longest_chain_cachesize = atomic_read(&num_drc_entries);
 391         } else if (entries == longest_chain) {
 392                 /* prefer to keep the smallest cachesize possible here */
 393                 longest_chain_cachesize = min_t(unsigned int,
 394                                 longest_chain_cachesize,
 395                                 atomic_read(&num_drc_entries));
 396         }
 397
 398         return ret;
 399 }
 400
 401 /*
 402  * Try to find an entry matching the current call in the cache. When none
 403  * is found, we try to grab the oldest expired entry off the LRU list. If
 404  * a suitable one isn't there, then drop the cache_lock and allocate a
 405  * new one, then search again in case one got inserted while this thread
 406  * didn't hold the lock.
 407  */
 408 int
 409 nfsd_cache_lookup(struct svc_rqst *rqstp)
 410 {
 411         struct svc_cacherep     *rp, *found;
 412         __be32                  xid = rqstp->rq_xid;
 413         u32                     proto =  rqstp->rq_prot,
 414                                 vers = rqstp->rq_vers,
 415                                 proc = rqstp->rq_proc;
 416         __wsum                  csum;
 417         u32 hash = nfsd_cache_hash(xid);
 418         struct nfsd_drc_bucket *b = &drc_hashtbl[hash];
 419         unsigned long           age;
 420         int type = rqstp->rq_cachetype;
 421         int rtn = RC_DOIT;
 422
 423         rqstp->rq_cacherep = NULL;
 424         if (type == RC_NOCACHE) {
 425                 nfsdstats.rcnocache++;
 426                 return rtn;
 427         }
 428
 429         csum = nfsd_cache_csum(rqstp);
 430
 431         /*
 432          * Since the common case is a cache miss followed by an insert,
 433          * preallocate an entry.
 434          */
 435         rp = nfsd_reply_cache_alloc();
 436         spin_lock(&b->cache_lock);
 437         if (likely(rp)) {
 438                 atomic_inc(&num_drc_entries);
 439                 drc_mem_usage += sizeof(*rp);
 440         }
 441
 442         /* go ahead and prune the cache */
 443         prune_bucket(b);
 444
 445         found = nfsd_cache_search(b, rqstp, csum);
 446         if (found) {
 447                 if (likely(rp))
 448                         nfsd_reply_cache_free_locked(rp);
 449                 rp = found;
 450                 goto found_entry;
 451         }
 452
 453         if (!rp) {
 454                 dprintk("nfsd: unable to allocate DRC entry!\n");
 455                 goto out;
 456         }
 457
 458         nfsdstats.rcmisses++;
 459         rqstp->rq_cacherep = rp;
 460         rp->c_state = RC_INPROG;
 461         rp->c_xid = xid;
 462         rp->c_proc = proc;
 463         rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
 464         rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
 465         rp->c_prot = proto;
 466         rp->c_vers = vers;
 467         rp->c_len = rqstp->rq_arg.len;
 468         rp->c_csum = csum;
 469
 470         lru_put_end(b, rp);
 471
 472         /* release any buffer */
 473         if (rp->c_type == RC_REPLBUFF) {
 474                 drc_mem_usage -= rp->c_replvec.iov_len;
 475                 kfree(rp->c_replvec.iov_base);
 476                 rp->c_replvec.iov_base = NULL;
 477         }
 478         rp->c_type = RC_NOCACHE;
 479  out:
 480         spin_unlock(&b->cache_lock);
 481         return rtn;
 482
 483 found_entry:
 484         nfsdstats.rchits++;
 485         /* We found a matching entry which is either in progress or done. */
 486         age = jiffies - rp->c_timestamp;
 487         lru_put_end(b, rp);
 488
 489         rtn = RC_DROPIT;
 490         /* Request being processed or excessive rexmits */
 491         if (rp->c_state == RC_INPROG || age < RC_DELAY)
 492                 goto out;
 493
 494         /* From the hall of fame of impractical attacks:
 495          * Is this a user who tries to snoop on the cache? */
 496         rtn = RC_DOIT;
 497         if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
 498                 goto out;
 499
 500         /* Compose RPC reply header */
 501         switch (rp->c_type) {
 502         case RC_NOCACHE:
 503                 break;
 504         case RC_REPLSTAT:
 505                 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
 506                 rtn = RC_REPLY;
 507                 break;
 508         case RC_REPLBUFF:
 509                 if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 510                         goto out;       /* should not happen */
 511                 rtn = RC_REPLY;
 512                 break;
 513         default:
 514                 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
 515                 nfsd_reply_cache_free_locked(rp);
 516         }
 517
 518         goto out;
 519 }
 520
 521 /*
 522  * Update a cache entry. This is called from nfsd_dispatch when
 523  * the procedure has been executed and the complete reply is in
 524  * rqstp->rq_res.
 525  *
 526  * We're copying around data here rather than swapping buffers because
 527  * the toplevel loop requires max-sized buffers, which would be a waste
 528  * of memory for a cache with a max reply size of 100 bytes (diropokres).
 529  *
 530  * If we should start to use different types of cache entries tailored
 531  * specifically for attrstat and fh's, we may save even more space.
 532  *
 533  * Also note that a cachetype of RC_NOCACHE can legally be passed when
 534  * nfsd failed to encode a reply that otherwise would have been cached.
 535  * In this case, nfsd_cache_update is called with statp == NULL.
 536  */
 537 void
 538 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
 539 {
 540         struct svc_cacherep *rp = rqstp->rq_cacherep;
 541         struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
 542         u32             hash;
 543         struct nfsd_drc_bucket *b;
 544         int             len;
 545         size_t          bufsize = 0;
 546
 547         if (!rp)
 548                 return;
 549
 550         hash = nfsd_cache_hash(rp->c_xid);
 551         b = &drc_hashtbl[hash];
 552
 553         len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
 554         len >>= 2;
 555
 556         /* Don't cache excessive amounts of data and XDR failures */
 557         if (!statp || len > (256 >> 2)) {
 558                 nfsd_reply_cache_free(b, rp);
 559                 return;
 560         }
 561
 562         switch (cachetype) {
 563         case RC_REPLSTAT:
 564                 if (len != 1)
 565                         printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
 566                 rp->c_replstat = *statp;
 567                 break;
 568         case RC_REPLBUFF:
 569                 cachv = &rp->c_replvec;
 570                 bufsize = len << 2;
 571                 cachv->iov_base = kmalloc(bufsize, GFP_KERNEL);
 572                 if (!cachv->iov_base) {
 573                         nfsd_reply_cache_free(b, rp);
 574                         return;
 575                 }
 576                 cachv->iov_len = bufsize;
 577                 memcpy(cachv->iov_base, statp, bufsize);
 578                 break;
 579         case RC_NOCACHE:
 580                 nfsd_reply_cache_free(b, rp);
 581                 return;
 582         }
 583         spin_lock(&b->cache_lock);
 584         drc_mem_usage += bufsize;
 585         lru_put_end(b, rp);
 586         rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
 587         rp->c_type = cachetype;
 588         rp->c_state = RC_DONE;
 589         spin_unlock(&b->cache_lock);
 590         return;
 591 }
 592
 593 /*
 594  * Copy cached reply to current reply buffer. Should always fit.
 595  * FIXME as reply is in a page, we should just attach the page, and
 596  * keep a refcount....
 597  */
 598 static int
 599 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
 600 {
 601         struct kvec     *vec = &rqstp->rq_res.head[0];
 602
 603         if (vec->iov_len + data->iov_len > PAGE_SIZE) {
 604                 printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
 605                                 data->iov_len);
 606                 return 0;
 607         }
 608         memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
 609         vec->iov_len += data->iov_len;
 610         return 1;
 611 }
 612
 613 /*
 614  * Note that fields may be added, removed or reordered in the future. Programs
 615  * scraping this file for info should test the labels to ensure they're
 616  * getting the correct field.
 617  */
 618 static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
 619 {
 620         seq_printf(m, "max entries:           %u\n", max_drc_entries);
 621         seq_printf(m, "num entries:           %u\n",
 622                         atomic_read(&num_drc_entries));
 623         seq_printf(m, "hash buckets:          %u\n", 1 << maskbits);
 624         seq_printf(m, "mem usage:             %u\n", drc_mem_usage);
 625         seq_printf(m, "cache hits:            %u\n", nfsdstats.rchits);
 626         seq_printf(m, "cache misses:          %u\n", nfsdstats.rcmisses);
 627         seq_printf(m, "not cached:            %u\n", nfsdstats.rcnocache);
 628         seq_printf(m, "payload misses:        %u\n", payload_misses);
 629         seq_printf(m, "longest chain len:     %u\n", longest_chain);
 630         seq_printf(m, "cachesize at longest:  %u\n", longest_chain_cachesize);
 631         return 0;
 632 }
 633
 634 int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
 635 {
 636         return single_open(file, nfsd_reply_cache_stats_show, NULL);
 637 }