/* * Request reply cache. This is currently a global cache, but this may * change in the future and be a per-client cache. * * This code is heavily inspired by the 44BSD implementation, although * it does things a bit differently. * * Copyright (C) 1995, 1996 Olaf Kirch */ #include #include #include #include #include #include #include "nfsd.h" #include "cache.h" #define NFSDDBG_FACILITY NFSDDBG_REPCACHE /* * We use this value to determine the number of hash buckets from the max * cache size, the idea being that when the cache is at its maximum number * of entries, then this should be the average number of entries per bucket. */ #define TARGET_BUCKET_SIZE 64 static struct hlist_head * cache_hash; static struct list_head lru_head; static struct kmem_cache *drc_slab; /* max number of entries allowed in the cache */ static unsigned int max_drc_entries; /* number of significant bits in the hash value */ static unsigned int maskbits; /* * Stats and other tracking of on the duplicate reply cache. All of these and * the "rc" fields in nfsdstats are protected by the cache_lock */ /* total number of entries */ static unsigned int num_drc_entries; /* cache misses due only to checksum comparison failures */ static unsigned int payload_misses; /* amount of memory (in bytes) currently consumed by the DRC */ static unsigned int drc_mem_usage; /* longest hash chain seen */ static unsigned int longest_chain; /* size of cache when we saw the longest hash chain */ static unsigned int longest_chain_cachesize; static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec); static void cache_cleaner_func(struct work_struct *unused); static int nfsd_reply_cache_shrink(struct shrinker *shrink, struct shrink_control *sc); struct shrinker nfsd_reply_cache_shrinker = { .shrink = nfsd_reply_cache_shrink, .seeks = 1, }; /* * locking for the reply cache: * A cache entry is "single use" if c_state == RC_INPROG * Otherwise, it when accessing _prev or _next, the lock must be held. */ static DEFINE_SPINLOCK(cache_lock); static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func); /* * Put a cap on the size of the DRC based on the amount of available * low memory in the machine. * * 64MB: 8192 * 128MB: 11585 * 256MB: 16384 * 512MB: 23170 * 1GB: 32768 * 2GB: 46340 * 4GB: 65536 * 8GB: 92681 * 16GB: 131072 * * ...with a hard cap of 256k entries. In the worst case, each entry will be * ~1k, so the above numbers should give a rough max of the amount of memory * used in k. */ static unsigned int nfsd_cache_size_limit(void) { unsigned int limit; unsigned long low_pages = totalram_pages - totalhigh_pages; limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10); return min_t(unsigned int, limit, 256*1024); } /* * Compute the number of hash buckets we need. Divide the max cachesize by * the "target" max bucket size, and round up to next power of two. */ static unsigned int nfsd_hashsize(unsigned int limit) { return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE); } static struct svc_cacherep * nfsd_reply_cache_alloc(void) { struct svc_cacherep *rp; rp = kmem_cache_alloc(drc_slab, GFP_KERNEL); if (rp) { rp->c_state = RC_UNUSED; rp->c_type = RC_NOCACHE; INIT_LIST_HEAD(&rp->c_lru); INIT_HLIST_NODE(&rp->c_hash); } return rp; } static void nfsd_reply_cache_free_locked(struct svc_cacherep *rp) { if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) { drc_mem_usage -= rp->c_replvec.iov_len; kfree(rp->c_replvec.iov_base); } if (!hlist_unhashed(&rp->c_hash)) hlist_del(&rp->c_hash); list_del(&rp->c_lru); --num_drc_entries; drc_mem_usage -= sizeof(*rp); kmem_cache_free(drc_slab, rp); } static void nfsd_reply_cache_free(struct svc_cacherep *rp) { spin_lock(&cache_lock); nfsd_reply_cache_free_locked(rp); spin_unlock(&cache_lock); } int nfsd_reply_cache_init(void) { unsigned int hashsize; INIT_LIST_HEAD(&lru_head); max_drc_entries = nfsd_cache_size_limit(); num_drc_entries = 0; hashsize = nfsd_hashsize(max_drc_entries); maskbits = ilog2(hashsize); register_shrinker(&nfsd_reply_cache_shrinker); drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep), 0, 0, NULL); if (!drc_slab) goto out_nomem; cache_hash = kcalloc(hashsize, sizeof(struct hlist_head), GFP_KERNEL); if (!cache_hash) goto out_nomem; return 0; out_nomem: printk(KERN_ERR "nfsd: failed to allocate reply cache\n"); nfsd_reply_cache_shutdown(); return -ENOMEM; } void nfsd_reply_cache_shutdown(void) { struct svc_cacherep *rp; unregister_shrinker(&nfsd_reply_cache_shrinker); cancel_delayed_work_sync(&cache_cleaner); while (!list_empty(&lru_head)) { rp = list_entry(lru_head.next, struct svc_cacherep, c_lru); nfsd_reply_cache_free_locked(rp); } kfree (cache_hash); cache_hash = NULL; if (drc_slab) { kmem_cache_destroy(drc_slab); drc_slab = NULL; } } /* * Move cache entry to end of LRU list, and queue the cleaner to run if it's * not already scheduled. */ static void lru_put_end(struct svc_cacherep *rp) { rp->c_timestamp = jiffies; list_move_tail(&rp->c_lru, &lru_head); schedule_delayed_work(&cache_cleaner, RC_EXPIRE); } /* * Move a cache entry from one hash list to another */ static void hash_refile(struct svc_cacherep *rp) { hlist_del_init(&rp->c_hash); hlist_add_head(&rp->c_hash, cache_hash + hash_32(rp->c_xid, maskbits)); } static inline bool nfsd_cache_entry_expired(struct svc_cacherep *rp) { return rp->c_state != RC_INPROG && time_after(jiffies, rp->c_timestamp + RC_EXPIRE); } /* * Walk the LRU list and prune off entries that are older than RC_EXPIRE. * Also prune the oldest ones when the total exceeds the max number of entries. */ static void prune_cache_entries(void) { struct svc_cacherep *rp, *tmp; list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) { if (!nfsd_cache_entry_expired(rp) && num_drc_entries <= max_drc_entries) break; nfsd_reply_cache_free_locked(rp); } /* * Conditionally rearm the job. If we cleaned out the list, then * cancel any pending run (since there won't be any work to do). * Otherwise, we rearm the job or modify the existing one to run in * RC_EXPIRE since we just ran the pruner. */ if (list_empty(&lru_head)) cancel_delayed_work(&cache_cleaner); else mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE); } static void cache_cleaner_func(struct work_struct *unused) { spin_lock(&cache_lock); prune_cache_entries(); spin_unlock(&cache_lock); } static int nfsd_reply_cache_shrink(struct shrinker *shrink, struct shrink_control *sc) { unsigned int num; spin_lock(&cache_lock); if (sc->nr_to_scan) prune_cache_entries(); num = num_drc_entries; spin_unlock(&cache_lock); return num; } /* * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes */ static __wsum nfsd_cache_csum(struct svc_rqst *rqstp) { int idx; unsigned int base; __wsum csum; struct xdr_buf *buf = &rqstp->rq_arg; const unsigned char *p = buf->head[0].iov_base; size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len, RC_CSUMLEN); size_t len = min(buf->head[0].iov_len, csum_len); /* rq_arg.head first */ csum = csum_partial(p, len, 0); csum_len -= len; /* Continue into page array */ idx = buf->page_base / PAGE_SIZE; base = buf->page_base & ~PAGE_MASK; while (csum_len) { p = page_address(buf->pages[idx]) + base; len = min_t(size_t, PAGE_SIZE - base, csum_len); csum = csum_partial(p, len, csum); csum_len -= len; base = 0; ++idx; } return csum; } static bool nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp) { /* Check RPC header info first */ if (rqstp->rq_xid != rp->c_xid || rqstp->rq_proc != rp->c_proc || rqstp->rq_prot != rp->c_prot || rqstp->rq_vers != rp->c_vers || rqstp->rq_arg.len != rp->c_len || !rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) || rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr)) return false; /* compare checksum of NFS data */ if (csum != rp->c_csum) { ++payload_misses; return false; } return true; } /* * Search the request hash for an entry that matches the given rqstp. * Must be called with cache_lock held. Returns the found entry or * NULL on failure. */ static struct svc_cacherep * nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum) { struct svc_cacherep *rp, *ret = NULL; struct hlist_head *rh; unsigned int entries = 0; rh = &cache_hash[hash_32(rqstp->rq_xid, maskbits)]; hlist_for_each_entry(rp, rh, c_hash) { ++entries; if (nfsd_cache_match(rqstp, csum, rp)) { ret = rp; break; } } /* tally hash chain length stats */ if (entries > longest_chain) { longest_chain = entries; longest_chain_cachesize = num_drc_entries; } else if (entries == longest_chain) { /* prefer to keep the smallest cachesize possible here */ longest_chain_cachesize = min(longest_chain_cachesize, num_drc_entries); } return ret; } /* * Try to find an entry matching the current call in the cache. When none * is found, we try to grab the oldest expired entry off the LRU list. If * a suitable one isn't there, then drop the cache_lock and allocate a * new one, then search again in case one got inserted while this thread * didn't hold the lock. */ int nfsd_cache_lookup(struct svc_rqst *rqstp) { struct svc_cacherep *rp, *found; __be32 xid = rqstp->rq_xid; u32 proto = rqstp->rq_prot, vers = rqstp->rq_vers, proc = rqstp->rq_proc; __wsum csum; unsigned long age; int type = rqstp->rq_cachetype; int rtn = RC_DOIT; rqstp->rq_cacherep = NULL; if (type == RC_NOCACHE) { nfsdstats.rcnocache++; return rtn; } csum = nfsd_cache_csum(rqstp); /* * Since the common case is a cache miss followed by an insert, * preallocate an entry. First, try to reuse the first entry on the LRU * if it works, then go ahead and prune the LRU list. */ spin_lock(&cache_lock); if (!list_empty(&lru_head)) { rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru); if (nfsd_cache_entry_expired(rp) || num_drc_entries >= max_drc_entries) { lru_put_end(rp); prune_cache_entries(); goto search_cache; } } /* No expired ones available, allocate a new one. */ spin_unlock(&cache_lock); rp = nfsd_reply_cache_alloc(); spin_lock(&cache_lock); if (likely(rp)) { ++num_drc_entries; drc_mem_usage += sizeof(*rp); } search_cache: found = nfsd_cache_search(rqstp, csum); if (found) { if (likely(rp)) nfsd_reply_cache_free_locked(rp); rp = found; goto found_entry; } if (!rp) { dprintk("nfsd: unable to allocate DRC entry!\n"); goto out; } /* * We're keeping the one we just allocated. Are we now over the * limit? Prune one off the tip of the LRU in trade for the one we * just allocated if so. */ if (num_drc_entries >= max_drc_entries) nfsd_reply_cache_free_locked(list_first_entry(&lru_head, struct svc_cacherep, c_lru)); nfsdstats.rcmisses++; rqstp->rq_cacherep = rp; rp->c_state = RC_INPROG; rp->c_xid = xid; rp->c_proc = proc; rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp)); rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp))); rp->c_prot = proto; rp->c_vers = vers; rp->c_len = rqstp->rq_arg.len; rp->c_csum = csum; hash_refile(rp); lru_put_end(rp); /* release any buffer */ if (rp->c_type == RC_REPLBUFF) { drc_mem_usage -= rp->c_replvec.iov_len; kfree(rp->c_replvec.iov_base); rp->c_replvec.iov_base = NULL; } rp->c_type = RC_NOCACHE; out: spin_unlock(&cache_lock); return rtn; found_entry: nfsdstats.rchits++; /* We found a matching entry which is either in progress or done. */ age = jiffies - rp->c_timestamp; lru_put_end(rp); rtn = RC_DROPIT; /* Request being processed or excessive rexmits */ if (rp->c_state == RC_INPROG || age < RC_DELAY) goto out; /* From the hall of fame of impractical attacks: * Is this a user who tries to snoop on the cache? */ rtn = RC_DOIT; if (!rqstp->rq_secure && rp->c_secure) goto out; /* Compose RPC reply header */ switch (rp->c_type) { case RC_NOCACHE: break; case RC_REPLSTAT: svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat); rtn = RC_REPLY; break; case RC_REPLBUFF: if (!nfsd_cache_append(rqstp, &rp->c_replvec)) goto out; /* should not happen */ rtn = RC_REPLY; break; default: printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type); nfsd_reply_cache_free_locked(rp); } goto out; } /* * Update a cache entry. This is called from nfsd_dispatch when * the procedure has been executed and the complete reply is in * rqstp->rq_res. * * We're copying around data here rather than swapping buffers because * the toplevel loop requires max-sized buffers, which would be a waste * of memory for a cache with a max reply size of 100 bytes (diropokres). * * If we should start to use different types of cache entries tailored * specifically for attrstat and fh's, we may save even more space. * * Also note that a cachetype of RC_NOCACHE can legally be passed when * nfsd failed to encode a reply that otherwise would have been cached. * In this case, nfsd_cache_update is called with statp == NULL. */ void nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp) { struct svc_cacherep *rp = rqstp->rq_cacherep; struct kvec *resv = &rqstp->rq_res.head[0], *cachv; int len; size_t bufsize = 0; if (!rp) return; len = resv->iov_len - ((char*)statp - (char*)resv->iov_base); len >>= 2; /* Don't cache excessive amounts of data and XDR failures */ if (!statp || len > (256 >> 2)) { nfsd_reply_cache_free(rp); return; } switch (cachetype) { case RC_REPLSTAT: if (len != 1) printk("nfsd: RC_REPLSTAT/reply len %d!\n",len); rp->c_replstat = *statp; break; case RC_REPLBUFF: cachv = &rp->c_replvec; bufsize = len << 2; cachv->iov_base = kmalloc(bufsize, GFP_KERNEL); if (!cachv->iov_base) { nfsd_reply_cache_free(rp); return; } cachv->iov_len = bufsize; memcpy(cachv->iov_base, statp, bufsize); break; case RC_NOCACHE: nfsd_reply_cache_free(rp); return; } spin_lock(&cache_lock); drc_mem_usage += bufsize; lru_put_end(rp); rp->c_secure = rqstp->rq_secure; rp->c_type = cachetype; rp->c_state = RC_DONE; spin_unlock(&cache_lock); return; } /* * Copy cached reply to current reply buffer. Should always fit. * FIXME as reply is in a page, we should just attach the page, and * keep a refcount.... */ static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data) { struct kvec *vec = &rqstp->rq_res.head[0]; if (vec->iov_len + data->iov_len > PAGE_SIZE) { printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n", data->iov_len); return 0; } memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len); vec->iov_len += data->iov_len; return 1; } /* * Note that fields may be added, removed or reordered in the future. Programs * scraping this file for info should test the labels to ensure they're * getting the correct field. */ static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v) { spin_lock(&cache_lock); seq_printf(m, "max entries: %u\n", max_drc_entries); seq_printf(m, "num entries: %u\n", num_drc_entries); seq_printf(m, "hash buckets: %u\n", 1 << maskbits); seq_printf(m, "mem usage: %u\n", drc_mem_usage); seq_printf(m, "cache hits: %u\n", nfsdstats.rchits); seq_printf(m, "cache misses: %u\n", nfsdstats.rcmisses); seq_printf(m, "not cached: %u\n", nfsdstats.rcnocache); seq_printf(m, "payload misses: %u\n", payload_misses); seq_printf(m, "longest chain len: %u\n", longest_chain); seq_printf(m, "cachesize at longest: %u\n", longest_chain_cachesize); spin_unlock(&cache_lock); return 0; } int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file) { return single_open(file, nfsd_reply_cache_stats_show, NULL); }