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![Chuck Lever](/assets/img/avatar_default.png)
DRC bucket pruning is done by nfsd_cache_lookup(), which is part of every NFSv2 and NFSv3 dispatch (ie, it's done while the client is waiting). I added a trace_printk() in prune_bucket() to see just how long it takes to prune. Here are two ends of the spectrum: prune_bucket: Scanned 1 and freed 0 in 90 ns, 62 entries remaining prune_bucket: Scanned 2 and freed 1 in 716 ns, 63 entries remaining ... prune_bucket: Scanned 75 and freed 74 in 34149 ns, 1 entries remaining Pruning latency is noticeable on fast transports with fast storage. By noticeable, I mean that the latency measured here in the worst case is the same order of magnitude as the round trip time for cached server operations. We could do something like moving expired entries to an expired list and then free them later instead of freeing them right in prune_bucket(). But simply limiting the number of entries that can be pruned by a lookup is simple and retains more entries in the cache, making the DRC somewhat more effective. Comparison with a 70/30 fio 8KB 12 thread direct I/O test: Before: write: IOPS=61.6k, BW=481MiB/s (505MB/s)(14.1GiB/30001msec); 0 zone resets WRITE: 1848726 ops (30%) avg bytes sent per op: 8340 avg bytes received per op: 136 backlog wait: 0.635158 RTT: 0.128525 total execute time: 0.827242 (milliseconds) After: write: IOPS=63.0k, BW=492MiB/s (516MB/s)(14.4GiB/30001msec); 0 zone resets WRITE: 1891144 ops (30%) avg bytes sent per op: 8340 avg bytes received per op: 136 backlog wait: 0.616114 RTT: 0.126842 total execute time: 0.805348 (milliseconds) Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
636 lines
17 KiB
C
636 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Request reply cache. This is currently a global cache, but this may
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* change in the future and be a per-client cache.
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*
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* This code is heavily inspired by the 44BSD implementation, although
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* it does things a bit differently.
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*
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* Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
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*/
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#include <linux/sunrpc/svc_xprt.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/sunrpc/addr.h>
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#include <linux/highmem.h>
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#include <linux/log2.h>
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#include <linux/hash.h>
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#include <net/checksum.h>
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#include "nfsd.h"
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#include "cache.h"
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#include "trace.h"
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/*
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* We use this value to determine the number of hash buckets from the max
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* cache size, the idea being that when the cache is at its maximum number
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* of entries, then this should be the average number of entries per bucket.
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*/
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#define TARGET_BUCKET_SIZE 64
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struct nfsd_drc_bucket {
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struct rb_root rb_head;
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struct list_head lru_head;
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spinlock_t cache_lock;
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};
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static struct kmem_cache *drc_slab;
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static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
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static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
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struct shrink_control *sc);
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static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
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struct shrink_control *sc);
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/*
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* Put a cap on the size of the DRC based on the amount of available
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* low memory in the machine.
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*
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* 64MB: 8192
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* 128MB: 11585
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* 256MB: 16384
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* 512MB: 23170
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* 1GB: 32768
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* 2GB: 46340
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* 4GB: 65536
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* 8GB: 92681
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* 16GB: 131072
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*
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* ...with a hard cap of 256k entries. In the worst case, each entry will be
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* ~1k, so the above numbers should give a rough max of the amount of memory
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* used in k.
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*
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* XXX: these limits are per-container, so memory used will increase
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* linearly with number of containers. Maybe that's OK.
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*/
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static unsigned int
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nfsd_cache_size_limit(void)
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{
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unsigned int limit;
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unsigned long low_pages = totalram_pages() - totalhigh_pages();
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limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
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return min_t(unsigned int, limit, 256*1024);
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}
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/*
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* Compute the number of hash buckets we need. Divide the max cachesize by
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* the "target" max bucket size, and round up to next power of two.
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*/
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static unsigned int
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nfsd_hashsize(unsigned int limit)
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{
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return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
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}
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static u32
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nfsd_cache_hash(__be32 xid, struct nfsd_net *nn)
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{
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return hash_32(be32_to_cpu(xid), nn->maskbits);
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}
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static struct svc_cacherep *
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nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum,
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struct nfsd_net *nn)
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{
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struct svc_cacherep *rp;
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rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
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if (rp) {
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rp->c_state = RC_UNUSED;
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rp->c_type = RC_NOCACHE;
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RB_CLEAR_NODE(&rp->c_node);
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INIT_LIST_HEAD(&rp->c_lru);
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memset(&rp->c_key, 0, sizeof(rp->c_key));
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rp->c_key.k_xid = rqstp->rq_xid;
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rp->c_key.k_proc = rqstp->rq_proc;
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rpc_copy_addr((struct sockaddr *)&rp->c_key.k_addr, svc_addr(rqstp));
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rpc_set_port((struct sockaddr *)&rp->c_key.k_addr, rpc_get_port(svc_addr(rqstp)));
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rp->c_key.k_prot = rqstp->rq_prot;
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rp->c_key.k_vers = rqstp->rq_vers;
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rp->c_key.k_len = rqstp->rq_arg.len;
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rp->c_key.k_csum = csum;
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}
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return rp;
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}
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static void
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nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
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struct nfsd_net *nn)
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{
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if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
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nfsd_stats_drc_mem_usage_sub(nn, rp->c_replvec.iov_len);
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kfree(rp->c_replvec.iov_base);
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}
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if (rp->c_state != RC_UNUSED) {
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rb_erase(&rp->c_node, &b->rb_head);
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list_del(&rp->c_lru);
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atomic_dec(&nn->num_drc_entries);
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nfsd_stats_drc_mem_usage_sub(nn, sizeof(*rp));
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}
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kmem_cache_free(drc_slab, rp);
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}
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static void
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nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
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struct nfsd_net *nn)
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{
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spin_lock(&b->cache_lock);
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nfsd_reply_cache_free_locked(b, rp, nn);
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spin_unlock(&b->cache_lock);
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}
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int nfsd_drc_slab_create(void)
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{
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drc_slab = kmem_cache_create("nfsd_drc",
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sizeof(struct svc_cacherep), 0, 0, NULL);
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return drc_slab ? 0: -ENOMEM;
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}
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void nfsd_drc_slab_free(void)
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{
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kmem_cache_destroy(drc_slab);
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}
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static int nfsd_reply_cache_stats_init(struct nfsd_net *nn)
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{
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return nfsd_percpu_counters_init(nn->counter, NFSD_NET_COUNTERS_NUM);
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}
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static void nfsd_reply_cache_stats_destroy(struct nfsd_net *nn)
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{
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nfsd_percpu_counters_destroy(nn->counter, NFSD_NET_COUNTERS_NUM);
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}
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int nfsd_reply_cache_init(struct nfsd_net *nn)
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{
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unsigned int hashsize;
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unsigned int i;
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int status = 0;
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nn->max_drc_entries = nfsd_cache_size_limit();
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atomic_set(&nn->num_drc_entries, 0);
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hashsize = nfsd_hashsize(nn->max_drc_entries);
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nn->maskbits = ilog2(hashsize);
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status = nfsd_reply_cache_stats_init(nn);
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if (status)
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goto out_nomem;
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nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
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nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
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nn->nfsd_reply_cache_shrinker.seeks = 1;
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status = register_shrinker(&nn->nfsd_reply_cache_shrinker);
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if (status)
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goto out_stats_destroy;
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nn->drc_hashtbl = kvzalloc(array_size(hashsize,
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sizeof(*nn->drc_hashtbl)), GFP_KERNEL);
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if (!nn->drc_hashtbl)
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goto out_shrinker;
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for (i = 0; i < hashsize; i++) {
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INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
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spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
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}
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nn->drc_hashsize = hashsize;
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return 0;
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out_shrinker:
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unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
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out_stats_destroy:
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nfsd_reply_cache_stats_destroy(nn);
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out_nomem:
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printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
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return -ENOMEM;
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}
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void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
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{
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struct svc_cacherep *rp;
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unsigned int i;
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nfsd_reply_cache_stats_destroy(nn);
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unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
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for (i = 0; i < nn->drc_hashsize; i++) {
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struct list_head *head = &nn->drc_hashtbl[i].lru_head;
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while (!list_empty(head)) {
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rp = list_first_entry(head, struct svc_cacherep, c_lru);
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nfsd_reply_cache_free_locked(&nn->drc_hashtbl[i],
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rp, nn);
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}
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}
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kvfree(nn->drc_hashtbl);
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nn->drc_hashtbl = NULL;
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nn->drc_hashsize = 0;
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}
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/*
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* Move cache entry to end of LRU list, and queue the cleaner to run if it's
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* not already scheduled.
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*/
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static void
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lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
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{
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rp->c_timestamp = jiffies;
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list_move_tail(&rp->c_lru, &b->lru_head);
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}
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static long prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn,
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unsigned int max)
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{
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struct svc_cacherep *rp, *tmp;
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long freed = 0;
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list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
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/*
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* Don't free entries attached to calls that are still
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* in-progress, but do keep scanning the list.
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*/
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if (rp->c_state == RC_INPROG)
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continue;
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if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
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time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
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break;
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nfsd_reply_cache_free_locked(b, rp, nn);
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if (max && freed++ > max)
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break;
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}
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return freed;
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}
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static long nfsd_prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn)
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{
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return prune_bucket(b, nn, 3);
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}
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/*
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* Walk the LRU list and prune off entries that are older than RC_EXPIRE.
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* Also prune the oldest ones when the total exceeds the max number of entries.
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*/
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static long
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prune_cache_entries(struct nfsd_net *nn)
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{
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unsigned int i;
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long freed = 0;
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for (i = 0; i < nn->drc_hashsize; i++) {
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struct nfsd_drc_bucket *b = &nn->drc_hashtbl[i];
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if (list_empty(&b->lru_head))
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continue;
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spin_lock(&b->cache_lock);
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freed += prune_bucket(b, nn, 0);
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spin_unlock(&b->cache_lock);
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}
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return freed;
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}
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static unsigned long
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nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
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{
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struct nfsd_net *nn = container_of(shrink,
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struct nfsd_net, nfsd_reply_cache_shrinker);
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return atomic_read(&nn->num_drc_entries);
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}
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static unsigned long
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nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
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{
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struct nfsd_net *nn = container_of(shrink,
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struct nfsd_net, nfsd_reply_cache_shrinker);
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return prune_cache_entries(nn);
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}
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/*
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* Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
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*/
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static __wsum
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nfsd_cache_csum(struct svc_rqst *rqstp)
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{
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int idx;
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unsigned int base;
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__wsum csum;
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struct xdr_buf *buf = &rqstp->rq_arg;
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const unsigned char *p = buf->head[0].iov_base;
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size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
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RC_CSUMLEN);
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size_t len = min(buf->head[0].iov_len, csum_len);
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/* rq_arg.head first */
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csum = csum_partial(p, len, 0);
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csum_len -= len;
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/* Continue into page array */
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idx = buf->page_base / PAGE_SIZE;
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base = buf->page_base & ~PAGE_MASK;
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while (csum_len) {
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p = page_address(buf->pages[idx]) + base;
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len = min_t(size_t, PAGE_SIZE - base, csum_len);
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csum = csum_partial(p, len, csum);
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csum_len -= len;
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base = 0;
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++idx;
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}
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return csum;
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}
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static int
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nfsd_cache_key_cmp(const struct svc_cacherep *key,
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const struct svc_cacherep *rp, struct nfsd_net *nn)
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{
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if (key->c_key.k_xid == rp->c_key.k_xid &&
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key->c_key.k_csum != rp->c_key.k_csum) {
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nfsd_stats_payload_misses_inc(nn);
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trace_nfsd_drc_mismatch(nn, key, rp);
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}
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return memcmp(&key->c_key, &rp->c_key, sizeof(key->c_key));
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}
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/*
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* Search the request hash for an entry that matches the given rqstp.
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* Must be called with cache_lock held. Returns the found entry or
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* inserts an empty key on failure.
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*/
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static struct svc_cacherep *
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nfsd_cache_insert(struct nfsd_drc_bucket *b, struct svc_cacherep *key,
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struct nfsd_net *nn)
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{
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struct svc_cacherep *rp, *ret = key;
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struct rb_node **p = &b->rb_head.rb_node,
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*parent = NULL;
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unsigned int entries = 0;
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int cmp;
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while (*p != NULL) {
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++entries;
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parent = *p;
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rp = rb_entry(parent, struct svc_cacherep, c_node);
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cmp = nfsd_cache_key_cmp(key, rp, nn);
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if (cmp < 0)
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p = &parent->rb_left;
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else if (cmp > 0)
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p = &parent->rb_right;
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else {
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ret = rp;
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goto out;
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}
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}
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rb_link_node(&key->c_node, parent, p);
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rb_insert_color(&key->c_node, &b->rb_head);
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out:
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/* tally hash chain length stats */
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if (entries > nn->longest_chain) {
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nn->longest_chain = entries;
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nn->longest_chain_cachesize = atomic_read(&nn->num_drc_entries);
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} else if (entries == nn->longest_chain) {
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/* prefer to keep the smallest cachesize possible here */
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nn->longest_chain_cachesize = min_t(unsigned int,
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nn->longest_chain_cachesize,
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atomic_read(&nn->num_drc_entries));
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}
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lru_put_end(b, ret);
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return ret;
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}
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/**
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* nfsd_cache_lookup - Find an entry in the duplicate reply cache
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* @rqstp: Incoming Call to find
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*
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* Try to find an entry matching the current call in the cache. When none
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* is found, we try to grab the oldest expired entry off the LRU list. If
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* a suitable one isn't there, then drop the cache_lock and allocate a
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* new one, then search again in case one got inserted while this thread
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* didn't hold the lock.
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*
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* Return values:
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* %RC_DOIT: Process the request normally
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* %RC_REPLY: Reply from cache
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* %RC_DROPIT: Do not process the request further
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*/
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int nfsd_cache_lookup(struct svc_rqst *rqstp)
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{
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struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
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struct svc_cacherep *rp, *found;
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__be32 xid = rqstp->rq_xid;
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__wsum csum;
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u32 hash = nfsd_cache_hash(xid, nn);
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struct nfsd_drc_bucket *b = &nn->drc_hashtbl[hash];
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int type = rqstp->rq_cachetype;
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int rtn = RC_DOIT;
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rqstp->rq_cacherep = NULL;
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if (type == RC_NOCACHE) {
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nfsd_stats_rc_nocache_inc();
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goto out;
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}
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csum = nfsd_cache_csum(rqstp);
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/*
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* Since the common case is a cache miss followed by an insert,
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* preallocate an entry.
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*/
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rp = nfsd_reply_cache_alloc(rqstp, csum, nn);
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if (!rp)
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goto out;
|
|
|
|
spin_lock(&b->cache_lock);
|
|
found = nfsd_cache_insert(b, rp, nn);
|
|
if (found != rp) {
|
|
nfsd_reply_cache_free_locked(NULL, rp, nn);
|
|
rp = found;
|
|
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_stats_rc_hits_inc();
|
|
rtn = RC_DROPIT;
|
|
|
|
/* 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:
|
|
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_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: Reply's status code
|
|
*
|
|
* 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;
|
|
u32 hash;
|
|
struct nfsd_drc_bucket *b;
|
|
int len;
|
|
size_t bufsize = 0;
|
|
|
|
if (!rp)
|
|
return;
|
|
|
|
hash = nfsd_cache_hash(rp->c_key.k_xid, nn);
|
|
b = &nn->drc_hashtbl[hash];
|
|
|
|
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.
|
|
*/
|
|
static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
|
|
{
|
|
struct nfsd_net *nn = m->private;
|
|
|
|
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;
|
|
}
|
|
|
|
int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
|
|
{
|
|
struct nfsd_net *nn = net_generic(file_inode(file)->i_sb->s_fs_info,
|
|
nfsd_net_id);
|
|
|
|
return single_open(file, nfsd_reply_cache_stats_show, nn);
|
|
}
|