fs/nfsd/nfscache.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * 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 <okir@monad.swb.de>
  */

 #include <linux/sunrpc/svc_xprt.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/sunrpc/addr.h>
 #include <linux/highmem.h>
 #include <linux/log2.h>
 #include <linux/hash.h>
 #include <net/checksum.h>

 #include "nfsd.h"
 #include "cache.h"
 #include "trace.h"

 /*
  * 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

 struct nfsd_drc_bucket {
 	struct rb_root rb_head;
 	struct list_head lru_head;
 	spinlock_t cache_lock;
 };

 static struct kmem_cache	*drc_slab;

 static int	nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
 static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
 					    struct shrink_control *sc);
 static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
 					   struct shrink_control *sc);

 /*
  * 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.
  *
  * XXX: these limits are per-container, so memory used will increase
  * linearly with number of containers.  Maybe that's OK.
  */
 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(struct svc_rqst *rqstp, __wsum csum,
 			struct nfsd_net *nn)
 {
 	struct svc_cacherep	*rp;

 	rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
 	if (rp) {
 		rp->c_state = RC_UNUSED;
 		rp->c_type = RC_NOCACHE;
 		RB_CLEAR_NODE(&rp->c_node);
 		INIT_LIST_HEAD(&rp->c_lru);

 		memset(&rp->c_key, 0, sizeof(rp->c_key));
 		rp->c_key.k_xid = rqstp->rq_xid;
 		rp->c_key.k_proc = rqstp->rq_proc;
 		rpc_copy_addr((struct sockaddr *)&rp->c_key.k_addr, svc_addr(rqstp));
 		rpc_set_port((struct sockaddr *)&rp->c_key.k_addr, rpc_get_port(svc_addr(rqstp)));
 		rp->c_key.k_prot = rqstp->rq_prot;
 		rp->c_key.k_vers = rqstp->rq_vers;
 		rp->c_key.k_len = rqstp->rq_arg.len;
 		rp->c_key.k_csum = csum;
 	}
 	return rp;
 }

 static void
 nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
 				struct nfsd_net *nn)
 {
 	if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
 		nfsd_stats_drc_mem_usage_sub(nn, rp->c_replvec.iov_len);
 		kfree(rp->c_replvec.iov_base);
 	}
 	if (rp->c_state != RC_UNUSED) {
 		rb_erase(&rp->c_node, &b->rb_head);
 		list_del(&rp->c_lru);
 		atomic_dec(&nn->num_drc_entries);
 		nfsd_stats_drc_mem_usage_sub(nn, sizeof(*rp));
 	}
 	kmem_cache_free(drc_slab, rp);
 }

 static void
 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
 			struct nfsd_net *nn)
 {
 	spin_lock(&b->cache_lock);
 	nfsd_reply_cache_free_locked(b, rp, nn);
 	spin_unlock(&b->cache_lock);
 }

 int nfsd_drc_slab_create(void)
 {
 	drc_slab = kmem_cache_create("nfsd_drc",
 				sizeof(struct svc_cacherep), 0, 0, NULL);
 	return drc_slab ? 0: -ENOMEM;
 }

 void nfsd_drc_slab_free(void)
 {
 	kmem_cache_destroy(drc_slab);
 }

 static int nfsd_reply_cache_stats_init(struct nfsd_net *nn)
 {
 	return nfsd_percpu_counters_init(nn->counter, NFSD_NET_COUNTERS_NUM);
 }

 static void nfsd_reply_cache_stats_destroy(struct nfsd_net *nn)
 {
 	nfsd_percpu_counters_destroy(nn->counter, NFSD_NET_COUNTERS_NUM);
 }

 int nfsd_reply_cache_init(struct nfsd_net *nn)
 {
 	unsigned int hashsize;
 	unsigned int i;
 	int status = 0;

 	nn->max_drc_entries = nfsd_cache_size_limit();
 	atomic_set(&nn->num_drc_entries, 0);
 	hashsize = nfsd_hashsize(nn->max_drc_entries);
 	nn->maskbits = ilog2(hashsize);

 	status = nfsd_reply_cache_stats_init(nn);
 	if (status)
 		goto out_nomem;

 	nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
 	nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
 	nn->nfsd_reply_cache_shrinker.seeks = 1;
 	status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
 				   "nfsd-reply:%s", nn->nfsd_name);
 	if (status)
 		goto out_stats_destroy;

 	nn->drc_hashtbl = kvzalloc(array_size(hashsize,
 				sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
 	if (!nn->drc_hashtbl)
 		goto out_shrinker;

 	for (i = 0; i < hashsize; i++) {
 		INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
 		spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
 	}
 	nn->drc_hashsize = hashsize;

 	return 0;
 out_shrinker:
 	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
 out_stats_destroy:
 	nfsd_reply_cache_stats_destroy(nn);
 out_nomem:
 	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 	return -ENOMEM;
 }

 void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
 {
 	struct svc_cacherep	*rp;
 	unsigned int i;

 	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);

 	for (i = 0; i < nn->drc_hashsize; i++) {
 		struct list_head *head = &nn->drc_hashtbl[i].lru_head;
 		while (!list_empty(head)) {
 			rp = list_first_entry(head, struct svc_cacherep, c_lru);
 			nfsd_reply_cache_free_locked(&nn->drc_hashtbl[i],
 									rp, nn);
 		}
 	}
 	nfsd_reply_cache_stats_destroy(nn);

 	kvfree(nn->drc_hashtbl);
 	nn->drc_hashtbl = NULL;
 	nn->drc_hashsize = 0;

 }

 /*
  * 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 nfsd_drc_bucket *b, struct svc_cacherep *rp)
 {
 	rp->c_timestamp = jiffies;
 	list_move_tail(&rp->c_lru, &b->lru_head);
 }

 static noinline struct nfsd_drc_bucket *
 nfsd_cache_bucket_find(__be32 xid, struct nfsd_net *nn)
 {
 	unsigned int hash = hash_32((__force u32)xid, nn->maskbits);

 	return &nn->drc_hashtbl[hash];
 }

 static long prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn,
 			 unsigned int max)
 {
 	struct svc_cacherep *rp, *tmp;
 	long freed = 0;

 	list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
 		/*
 		 * Don't free entries attached to calls that are still
 		 * in-progress, but do keep scanning the list.
 		 */
 		if (rp->c_state == RC_INPROG)
 			continue;
 		if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
 		    time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
 			break;
 		nfsd_reply_cache_free_locked(b, rp, nn);
 		if (max && freed++ > max)
 			break;
 	}
 	return freed;
 }

 static long nfsd_prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn)
 {
 	return prune_bucket(b, nn, 3);
 }

 /*
  * 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 long
 prune_cache_entries(struct nfsd_net *nn)
 {
 	unsigned int i;
 	long freed = 0;

 	for (i = 0; i < nn->drc_hashsize; i++) {
 		struct nfsd_drc_bucket *b = &nn->drc_hashtbl[i];

 		if (list_empty(&b->lru_head))
 			continue;
 		spin_lock(&b->cache_lock);
 		freed += prune_bucket(b, nn, 0);
 		spin_unlock(&b->cache_lock);
 	}
 	return freed;
 }

 static unsigned long
 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 {
 	struct nfsd_net *nn = container_of(shrink,
 				struct nfsd_net, nfsd_reply_cache_shrinker);

 	return atomic_read(&nn->num_drc_entries);
 }

 static unsigned long
 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
 	struct nfsd_net *nn = container_of(shrink,
 				struct nfsd_net, nfsd_reply_cache_shrinker);

 	return prune_cache_entries(nn);
 }
 /*
  * 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 int
 nfsd_cache_key_cmp(const struct svc_cacherep *key,
 			const struct svc_cacherep *rp, struct nfsd_net *nn)
 {
 	if (key->c_key.k_xid == rp->c_key.k_xid &&
 	    key->c_key.k_csum != rp->c_key.k_csum) {
 		nfsd_stats_payload_misses_inc(nn);
 		trace_nfsd_drc_mismatch(nn, key, rp);
 	}

 	return memcmp(&key->c_key, &rp->c_key, sizeof(key->c_key));
 }

 /*
  * Search the request hash for an entry that matches the given rqstp.
  * Must be called with cache_lock held. Returns the found entry or
  * inserts an empty key on failure.
  */
 static struct svc_cacherep *
 nfsd_cache_insert(struct nfsd_drc_bucket *b, struct svc_cacherep *key,
 			struct nfsd_net *nn)
 {
 	struct svc_cacherep	*rp, *ret = key;
 	struct rb_node		**p = &b->rb_head.rb_node,
 				*parent = NULL;
 	unsigned int		entries = 0;
 	int cmp;

 	while (*p != NULL) {
 		++entries;
 		parent = *p;
 		rp = rb_entry(parent, struct svc_cacherep, c_node);

 		cmp = nfsd_cache_key_cmp(key, rp, nn);
 		if (cmp < 0)
 			p = &parent->rb_left;
 		else if (cmp > 0)
 			p = &parent->rb_right;
 		else {
 			ret = rp;
 			goto out;
 		}
 	}
 	rb_link_node(&key->c_node, parent, p);
 	rb_insert_color(&key->c_node, &b->rb_head);
 out:
 	/* tally hash chain length stats */
 	if (entries > nn->longest_chain) {
 		nn->longest_chain = entries;
 		nn->longest_chain_cachesize = atomic_read(&nn->num_drc_entries);
 	} else if (entries == nn->longest_chain) {
 		/* prefer to keep the smallest cachesize possible here */
 		nn->longest_chain_cachesize = min_t(unsigned int,
 				nn->longest_chain_cachesize,
 				atomic_read(&nn->num_drc_entries));
 	}

 	lru_put_end(b, ret);
 	return ret;
 }

 /**
  * nfsd_cache_lookup - Find an entry in the duplicate reply cache
  * @rqstp: Incoming Call to find
  *
  * 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.
  *
  * Return values:
  *   %RC_DOIT: Process the request normally
  *   %RC_REPLY: Reply from cache
  *   %RC_DROPIT: Do not process the request further
  */
 int nfsd_cache_lookup(struct svc_rqst *rqstp)
 {
 	struct nfsd_net		*nn;
 	struct svc_cacherep	*rp, *found;
 	__wsum			csum;
 	struct nfsd_drc_bucket	*b;
 	int type = rqstp->rq_cachetype;
 	int rtn = RC_DOIT;

 	rqstp->rq_cacherep = NULL;
 	if (type == RC_NOCACHE) {
 		nfsd_stats_rc_nocache_inc();
 		goto out;
 	}

 	csum = nfsd_cache_csum(rqstp);

 	/*
 	 * Since the common case is a cache miss followed by an insert,
 	 * preallocate an entry.
 	 */
 	nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 	rp = nfsd_reply_cache_alloc(rqstp, csum, nn);
 	if (!rp)
 		goto out;

 	b = nfsd_cache_bucket_find(rqstp->rq_xid, nn);
 	spin_lock(&b->cache_lock);
 	found = nfsd_cache_insert(b, rp, nn);
 	if (found != rp)
 		goto found_entry;

 	nfsd_stats_rc_misses_inc();
 	rqstp->rq_cacherep = rp;
 	rp->c_state = RC_INPROG;

 	atomic_inc(&nn->num_drc_entries);
 	nfsd_stats_drc_mem_usage_add(nn, sizeof(*rp));

 	nfsd_prune_bucket(b, nn);

 out_unlock:
 	spin_unlock(&b->cache_lock);
 out:
 	return rtn;

 found_entry:
 	/* We found a matching entry which is either in progress or done. */
 	nfsd_reply_cache_free_locked(NULL, rp, nn);
 	nfsd_stats_rc_hits_inc();
 	rtn = RC_DROPIT;
 	rp = found;

 	/* Request being processed */
 	if (rp->c_state == RC_INPROG)
 		goto out_trace;

 	/* From the hall of fame of impractical attacks:
 	 * Is this a user who tries to snoop on the cache? */
 	rtn = RC_DOIT;
 	if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
 		goto out_trace;

 	/* Compose RPC reply header */
 	switch (rp->c_type) {
 	case RC_NOCACHE:
 		break;
 	case RC_REPLSTAT:
 		xdr_stream_encode_be32(&rqstp->rq_res_stream, rp->c_replstat);
 		rtn = RC_REPLY;
 		break;
 	case RC_REPLBUFF:
 		if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 			goto out_unlock; /* should not happen */
 		rtn = RC_REPLY;
 		break;
 	default:
 		WARN_ONCE(1, "nfsd: bad repcache type %d\n", rp->c_type);
 	}

 out_trace:
 	trace_nfsd_drc_found(nn, rqstp, rtn);
 	goto out_unlock;
 }

 /**
  * nfsd_cache_update - Update an entry in the duplicate reply cache.
  * @rqstp: svc_rqst with a finished Reply
  * @cachetype: which cache to update
  * @statp: pointer to Reply's NFS status code, or NULL
  *
  * 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 nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 	struct svc_cacherep *rp = rqstp->rq_cacherep;
 	struct kvec	*resv = &rqstp->rq_res.head[0], *cachv;
 	struct nfsd_drc_bucket *b;
 	int		len;
 	size_t		bufsize = 0;

 	if (!rp)
 		return;

 	b = nfsd_cache_bucket_find(rp->c_key.k_xid, nn);

 	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(b, rp, nn);
 		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(b, rp, nn);
 			return;
 		}
 		cachv->iov_len = bufsize;
 		memcpy(cachv->iov_base, statp, bufsize);
 		break;
 	case RC_NOCACHE:
 		nfsd_reply_cache_free(b, rp, nn);
 		return;
 	}
 	spin_lock(&b->cache_lock);
 	nfsd_stats_drc_mem_usage_add(nn, bufsize);
 	lru_put_end(b, rp);
 	rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
 	rp->c_type = cachetype;
 	rp->c_state = RC_DONE;
 	spin_unlock(&b->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.
  */
 int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
 {
 	struct nfsd_net *nn = net_generic(file_inode(m->file)->i_sb->s_fs_info,
 					  nfsd_net_id);

 	seq_printf(m, "max entries:           %u\n", nn->max_drc_entries);
 	seq_printf(m, "num entries:           %u\n",
 		   atomic_read(&nn->num_drc_entries));
 	seq_printf(m, "hash buckets:          %u\n", 1 << nn->maskbits);
 	seq_printf(m, "mem usage:             %lld\n",
 		   percpu_counter_sum_positive(&nn->counter[NFSD_NET_DRC_MEM_USAGE]));
 	seq_printf(m, "cache hits:            %lld\n",
 		   percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_HITS]));
 	seq_printf(m, "cache misses:          %lld\n",
 		   percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_MISSES]));
 	seq_printf(m, "not cached:            %lld\n",
 		   percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_NOCACHE]));
 	seq_printf(m, "payload misses:        %lld\n",
 		   percpu_counter_sum_positive(&nn->counter[NFSD_NET_PAYLOAD_MISSES]));
 	seq_printf(m, "longest chain len:     %u\n", nn->longest_chain);
 	seq_printf(m, "cachesize at longest:  %u\n", nn->longest_chain_cachesize);
 	return 0;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* 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 <okir@monad.swb.de>
	*/

	#include <linux/sunrpc/svc_xprt.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/sunrpc/addr.h>
	#include <linux/highmem.h>
	#include <linux/log2.h>
	#include <linux/hash.h>
	#include <net/checksum.h>

	#include "nfsd.h"
	#include "cache.h"
	#include "trace.h"

	/*
	* 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

	struct nfsd_drc_bucket {
	struct rb_root rb_head;
	struct list_head lru_head;
	spinlock_t cache_lock;
	};

	static struct kmem_cache *drc_slab;

	static int nfsd_cache_append(struct svc_rqst rqstp, struct kvec vec);
	static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
	struct shrink_control *sc);
	static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
	struct shrink_control *sc);

	/*
	* 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.
	*
	* XXX: these limits are per-container, so memory used will increase
	* linearly with number of containers. Maybe that's OK.
	*/
	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(struct svc_rqst *rqstp, __wsum csum,
	struct nfsd_net *nn)
	{
	struct svc_cacherep *rp;

	rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
	if (rp) {
	rp->c_state = RC_UNUSED;
	rp->c_type = RC_NOCACHE;
	RB_CLEAR_NODE(&rp->c_node);
	INIT_LIST_HEAD(&rp->c_lru);

	memset(&rp->c_key, 0, sizeof(rp->c_key));
	rp->c_key.k_xid = rqstp->rq_xid;
	rp->c_key.k_proc = rqstp->rq_proc;
	rpc_copy_addr((struct sockaddr *)&rp->c_key.k_addr, svc_addr(rqstp));
	rpc_set_port((struct sockaddr *)&rp->c_key.k_addr, rpc_get_port(svc_addr(rqstp)));
	rp->c_key.k_prot = rqstp->rq_prot;
	rp->c_key.k_vers = rqstp->rq_vers;
	rp->c_key.k_len = rqstp->rq_arg.len;
	rp->c_key.k_csum = csum;
	}
	return rp;
	}

	static void
	nfsd_reply_cache_free_locked(struct nfsd_drc_bucket b, struct svc_cacherep rp,
	struct nfsd_net *nn)
	{
	if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
	nfsd_stats_drc_mem_usage_sub(nn, rp->c_replvec.iov_len);
	kfree(rp->c_replvec.iov_base);
	}
	if (rp->c_state != RC_UNUSED) {
	rb_erase(&rp->c_node, &b->rb_head);
	list_del(&rp->c_lru);
	atomic_dec(&nn->num_drc_entries);
	nfsd_stats_drc_mem_usage_sub(nn, sizeof(*rp));
	}
	kmem_cache_free(drc_slab, rp);
	}

	static void
	nfsd_reply_cache_free(struct nfsd_drc_bucket b, struct svc_cacherep rp,
	struct nfsd_net *nn)
	{
	spin_lock(&b->cache_lock);
	nfsd_reply_cache_free_locked(b, rp, nn);
	spin_unlock(&b->cache_lock);
	}

	int nfsd_drc_slab_create(void)
	{
	drc_slab = kmem_cache_create("nfsd_drc",
	sizeof(struct svc_cacherep), 0, 0, NULL);
	return drc_slab ? 0: -ENOMEM;
	}

	void nfsd_drc_slab_free(void)
	{
	kmem_cache_destroy(drc_slab);
	}

	static int nfsd_reply_cache_stats_init(struct nfsd_net *nn)
	{
	return nfsd_percpu_counters_init(nn->counter, NFSD_NET_COUNTERS_NUM);
	}

	static void nfsd_reply_cache_stats_destroy(struct nfsd_net *nn)
	{
	nfsd_percpu_counters_destroy(nn->counter, NFSD_NET_COUNTERS_NUM);
	}

	int nfsd_reply_cache_init(struct nfsd_net *nn)
	{
	unsigned int hashsize;
	unsigned int i;
	int status = 0;

	nn->max_drc_entries = nfsd_cache_size_limit();
	atomic_set(&nn->num_drc_entries, 0);
	hashsize = nfsd_hashsize(nn->max_drc_entries);
	nn->maskbits = ilog2(hashsize);

	status = nfsd_reply_cache_stats_init(nn);
	if (status)
	goto out_nomem;

	nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
	nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
	nn->nfsd_reply_cache_shrinker.seeks = 1;
	status = register_shrinker(&nn->nfsd_reply_cache_shrinker,
	"nfsd-reply:%s", nn->nfsd_name);
	if (status)
	goto out_stats_destroy;

	nn->drc_hashtbl = kvzalloc(array_size(hashsize,
	sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
	if (!nn->drc_hashtbl)
	goto out_shrinker;

	for (i = 0; i < hashsize; i++) {
	INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
	spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
	}
	nn->drc_hashsize = hashsize;

	return 0;
	out_shrinker:
	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
	out_stats_destroy:
	nfsd_reply_cache_stats_destroy(nn);
	out_nomem:
	printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
	return -ENOMEM;
	}

	void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
	{
	struct svc_cacherep *rp;
	unsigned int i;

	unregister_shrinker(&nn->nfsd_reply_cache_shrinker);

	for (i = 0; i < nn->drc_hashsize; i++) {
	struct list_head *head = &nn->drc_hashtbl[i].lru_head;
	while (!list_empty(head)) {
	rp = list_first_entry(head, struct svc_cacherep, c_lru);
	nfsd_reply_cache_free_locked(&nn->drc_hashtbl[i],
	rp, nn);
	}
	}
	nfsd_reply_cache_stats_destroy(nn);

	kvfree(nn->drc_hashtbl);
	nn->drc_hashtbl = NULL;
	nn->drc_hashsize = 0;

	}

	/*
	* 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 nfsd_drc_bucket b, struct svc_cacherep rp)
	{
	rp->c_timestamp = jiffies;
	list_move_tail(&rp->c_lru, &b->lru_head);
	}

	static noinline struct nfsd_drc_bucket *
	nfsd_cache_bucket_find(__be32 xid, struct nfsd_net *nn)
	{
	unsigned int hash = hash_32((__force u32)xid, nn->maskbits);

	return &nn->drc_hashtbl[hash];
	}

	static long prune_bucket(struct nfsd_drc_bucket b, struct nfsd_net nn,
	unsigned int max)
	{
	struct svc_cacherep rp, tmp;
	long freed = 0;

	list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
	/*
	* Don't free entries attached to calls that are still
	* in-progress, but do keep scanning the list.
	*/
	if (rp->c_state == RC_INPROG)
	continue;
	if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
	time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
	break;
	nfsd_reply_cache_free_locked(b, rp, nn);
	if (max && freed++ > max)
	break;
	}
	return freed;
	}

	static long nfsd_prune_bucket(struct nfsd_drc_bucket b, struct nfsd_net nn)
	{
	return prune_bucket(b, nn, 3);
	}

	/*
	* 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 long
	prune_cache_entries(struct nfsd_net *nn)
	{
	unsigned int i;
	long freed = 0;

	for (i = 0; i < nn->drc_hashsize; i++) {
	struct nfsd_drc_bucket *b = &nn->drc_hashtbl[i];

	if (list_empty(&b->lru_head))
	continue;
	spin_lock(&b->cache_lock);
	freed += prune_bucket(b, nn, 0);
	spin_unlock(&b->cache_lock);
	}
	return freed;
	}

	static unsigned long
	nfsd_reply_cache_count(struct shrinker shrink, struct shrink_control sc)
	{
	struct nfsd_net *nn = container_of(shrink,
	struct nfsd_net, nfsd_reply_cache_shrinker);

	return atomic_read(&nn->num_drc_entries);
	}

	static unsigned long
	nfsd_reply_cache_scan(struct shrinker shrink, struct shrink_control sc)
	{
	struct nfsd_net *nn = container_of(shrink,
	struct nfsd_net, nfsd_reply_cache_shrinker);

	return prune_cache_entries(nn);
	}
	/*
	* 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 int
	nfsd_cache_key_cmp(const struct svc_cacherep *key,
	const struct svc_cacherep rp, struct nfsd_net nn)
	{
	if (key->c_key.k_xid == rp->c_key.k_xid &&
	key->c_key.k_csum != rp->c_key.k_csum) {
	nfsd_stats_payload_misses_inc(nn);
	trace_nfsd_drc_mismatch(nn, key, rp);
	}

	return memcmp(&key->c_key, &rp->c_key, sizeof(key->c_key));
	}

	/*
	* Search the request hash for an entry that matches the given rqstp.
	* Must be called with cache_lock held. Returns the found entry or
	* inserts an empty key on failure.
	*/
	static struct svc_cacherep *
	nfsd_cache_insert(struct nfsd_drc_bucket b, struct svc_cacherep key,
	struct nfsd_net *nn)
	{
	struct svc_cacherep rp, ret = key;
	struct rb_node **p = &b->rb_head.rb_node,
	*parent = NULL;
	unsigned int entries = 0;
	int cmp;

	while (*p != NULL) {
	++entries;
	parent = *p;
	rp = rb_entry(parent, struct svc_cacherep, c_node);

	cmp = nfsd_cache_key_cmp(key, rp, nn);
	if (cmp < 0)
	p = &parent->rb_left;
	else if (cmp > 0)
	p = &parent->rb_right;
	else {
	ret = rp;
	goto out;
	}
	}
	rb_link_node(&key->c_node, parent, p);
	rb_insert_color(&key->c_node, &b->rb_head);
	out:
	/* tally hash chain length stats */
	if (entries > nn->longest_chain) {
	nn->longest_chain = entries;
	nn->longest_chain_cachesize = atomic_read(&nn->num_drc_entries);
	} else if (entries == nn->longest_chain) {
	/* prefer to keep the smallest cachesize possible here */
	nn->longest_chain_cachesize = min_t(unsigned int,
	nn->longest_chain_cachesize,
	atomic_read(&nn->num_drc_entries));
	}

	lru_put_end(b, ret);
	return ret;
	}

	/**
	* nfsd_cache_lookup - Find an entry in the duplicate reply cache
	* @rqstp: Incoming Call to find
	*
	* 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.
	*
	* Return values:
	* %RC_DOIT: Process the request normally
	* %RC_REPLY: Reply from cache
	* %RC_DROPIT: Do not process the request further
	*/
	int nfsd_cache_lookup(struct svc_rqst *rqstp)
	{
	struct nfsd_net *nn;
	struct svc_cacherep rp, found;
	__wsum csum;
	struct nfsd_drc_bucket *b;
	int type = rqstp->rq_cachetype;
	int rtn = RC_DOIT;

	rqstp->rq_cacherep = NULL;
	if (type == RC_NOCACHE) {
	nfsd_stats_rc_nocache_inc();
	goto out;
	}

	csum = nfsd_cache_csum(rqstp);

	/*
	* Since the common case is a cache miss followed by an insert,
	* preallocate an entry.
	*/
	nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
	rp = nfsd_reply_cache_alloc(rqstp, csum, nn);
	if (!rp)
	goto out;

	b = nfsd_cache_bucket_find(rqstp->rq_xid, nn);
	spin_lock(&b->cache_lock);
	found = nfsd_cache_insert(b, rp, nn);
	if (found != rp)
	goto found_entry;

	nfsd_stats_rc_misses_inc();
	rqstp->rq_cacherep = rp;
	rp->c_state = RC_INPROG;

	atomic_inc(&nn->num_drc_entries);
	nfsd_stats_drc_mem_usage_add(nn, sizeof(*rp));

	nfsd_prune_bucket(b, nn);

	out_unlock:
	spin_unlock(&b->cache_lock);
	out:
	return rtn;

	found_entry:
	/* We found a matching entry which is either in progress or done. */
	nfsd_reply_cache_free_locked(NULL, rp, nn);
	nfsd_stats_rc_hits_inc();
	rtn = RC_DROPIT;
	rp = found;

	/* Request being processed */
	if (rp->c_state == RC_INPROG)
	goto out_trace;

	/* From the hall of fame of impractical attacks:
	* Is this a user who tries to snoop on the cache? */
	rtn = RC_DOIT;
	if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
	goto out_trace;

	/* Compose RPC reply header */
	switch (rp->c_type) {
	case RC_NOCACHE:
	break;
	case RC_REPLSTAT:
	xdr_stream_encode_be32(&rqstp->rq_res_stream, rp->c_replstat);
	rtn = RC_REPLY;
	break;
	case RC_REPLBUFF:
	if (!nfsd_cache_append(rqstp, &rp->c_replvec))
	goto out_unlock; /* should not happen */
	rtn = RC_REPLY;
	break;
	default:
	WARN_ONCE(1, "nfsd: bad repcache type %d\n", rp->c_type);
	}

	out_trace:
	trace_nfsd_drc_found(nn, rqstp, rtn);
	goto out_unlock;
	}

	/**
	* nfsd_cache_update - Update an entry in the duplicate reply cache.
	* @rqstp: svc_rqst with a finished Reply
	* @cachetype: which cache to update
	* @statp: pointer to Reply's NFS status code, or NULL
	*
	* 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 nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
	struct svc_cacherep *rp = rqstp->rq_cacherep;
	struct kvec resv = &rqstp->rq_res.head[0], cachv;
	struct nfsd_drc_bucket *b;
	int len;
	size_t bufsize = 0;

	if (!rp)
	return;

	b = nfsd_cache_bucket_find(rp->c_key.k_xid, nn);

	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(b, rp, nn);
	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(b, rp, nn);
	return;
	}
	cachv->iov_len = bufsize;
	memcpy(cachv->iov_base, statp, bufsize);
	break;
	case RC_NOCACHE:
	nfsd_reply_cache_free(b, rp, nn);
	return;
	}
	spin_lock(&b->cache_lock);
	nfsd_stats_drc_mem_usage_add(nn, bufsize);
	lru_put_end(b, rp);
	rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
	rp->c_type = cachetype;
	rp->c_state = RC_DONE;
	spin_unlock(&b->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.
	*/
	int nfsd_reply_cache_stats_show(struct seq_file m, void v)
	{
	struct nfsd_net *nn = net_generic(file_inode(m->file)->i_sb->s_fs_info,
	nfsd_net_id);

	seq_printf(m, "max entries: %u\n", nn->max_drc_entries);
	seq_printf(m, "num entries: %u\n",
	atomic_read(&nn->num_drc_entries));
	seq_printf(m, "hash buckets: %u\n", 1 << nn->maskbits);
	seq_printf(m, "mem usage: %lld\n",
	percpu_counter_sum_positive(&nn->counter[NFSD_NET_DRC_MEM_USAGE]));
	seq_printf(m, "cache hits: %lld\n",
	percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_HITS]));
	seq_printf(m, "cache misses: %lld\n",
	percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_MISSES]));
	seq_printf(m, "not cached: %lld\n",
	percpu_counter_sum_positive(&nfsdstats.counter[NFSD_STATS_RC_NOCACHE]));
	seq_printf(m, "payload misses: %lld\n",
	percpu_counter_sum_positive(&nn->counter[NFSD_NET_PAYLOAD_MISSES]));
	seq_printf(m, "longest chain len: %u\n", nn->longest_chain);
	seq_printf(m, "cachesize at longest: %u\n", nn->longest_chain_cachesize);
	return 0;
	}