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Linux/fs/nfsd/nfscache.c

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  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 }
638 

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