![Jeff Layton](/assets/img/avatar_default.png)
It's not sufficient to only clean the cache when requests come in. What if we have a flurry of activity and then the server goes idle? Add a workqueue job that will clean the cache every RC_EXPIRE period. Care is taken to only run this when we expect to have entries expiring. Signed-off-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
459 lines
11 KiB
C
459 lines
11 KiB
C
/*
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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/slab.h>
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#include <linux/sunrpc/clnt.h>
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#include <linux/highmem.h>
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#include "nfsd.h"
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#include "cache.h"
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#define NFSDDBG_FACILITY NFSDDBG_REPCACHE
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#define HASHSIZE 64
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static struct hlist_head * cache_hash;
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static struct list_head lru_head;
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static struct kmem_cache *drc_slab;
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static unsigned int num_drc_entries;
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static unsigned int max_drc_entries;
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/*
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* Calculate the hash index from an XID.
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*/
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static inline u32 request_hash(u32 xid)
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{
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u32 h = xid;
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h ^= (xid >> 24);
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return h & (HASHSIZE-1);
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}
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static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
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static void cache_cleaner_func(struct work_struct *unused);
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/*
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* locking for the reply cache:
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* A cache entry is "single use" if c_state == RC_INPROG
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* Otherwise, it when accessing _prev or _next, the lock must be held.
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*/
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static DEFINE_SPINLOCK(cache_lock);
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static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func);
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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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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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static struct svc_cacherep *
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nfsd_reply_cache_alloc(void)
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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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INIT_LIST_HEAD(&rp->c_lru);
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INIT_HLIST_NODE(&rp->c_hash);
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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 svc_cacherep *rp)
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{
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if (rp->c_type == RC_REPLBUFF)
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kfree(rp->c_replvec.iov_base);
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hlist_del(&rp->c_hash);
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list_del(&rp->c_lru);
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--num_drc_entries;
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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 svc_cacherep *rp)
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{
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spin_lock(&cache_lock);
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nfsd_reply_cache_free_locked(rp);
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spin_unlock(&cache_lock);
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}
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int nfsd_reply_cache_init(void)
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{
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drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
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0, 0, NULL);
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if (!drc_slab)
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goto out_nomem;
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cache_hash = kcalloc(HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
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if (!cache_hash)
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goto out_nomem;
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INIT_LIST_HEAD(&lru_head);
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max_drc_entries = nfsd_cache_size_limit();
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num_drc_entries = 0;
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return 0;
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out_nomem:
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printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
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nfsd_reply_cache_shutdown();
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return -ENOMEM;
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}
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void nfsd_reply_cache_shutdown(void)
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{
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struct svc_cacherep *rp;
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cancel_delayed_work_sync(&cache_cleaner);
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while (!list_empty(&lru_head)) {
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rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
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nfsd_reply_cache_free_locked(rp);
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}
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kfree (cache_hash);
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cache_hash = NULL;
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if (drc_slab) {
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kmem_cache_destroy(drc_slab);
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drc_slab = NULL;
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}
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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 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, &lru_head);
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schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
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}
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/*
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* Move a cache entry from one hash list to another
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*/
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static void
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hash_refile(struct svc_cacherep *rp)
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{
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hlist_del_init(&rp->c_hash);
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hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
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}
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static inline bool
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nfsd_cache_entry_expired(struct svc_cacherep *rp)
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{
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return rp->c_state != RC_INPROG &&
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time_after(jiffies, rp->c_timestamp + RC_EXPIRE);
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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 void
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prune_cache_entries(void)
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{
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struct svc_cacherep *rp, *tmp;
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list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) {
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if (!nfsd_cache_entry_expired(rp) &&
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num_drc_entries <= max_drc_entries)
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break;
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nfsd_reply_cache_free_locked(rp);
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}
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/*
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* Conditionally rearm the job. If we cleaned out the list, then
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* cancel any pending run (since there won't be any work to do).
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* Otherwise, we rearm the job or modify the existing one to run in
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* RC_EXPIRE since we just ran the pruner.
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*/
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if (list_empty(&lru_head))
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cancel_delayed_work(&cache_cleaner);
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else
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mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
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}
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static void
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cache_cleaner_func(struct work_struct *unused)
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{
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spin_lock(&cache_lock);
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prune_cache_entries();
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spin_unlock(&cache_lock);
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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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* NULL on failure.
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*/
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static struct svc_cacherep *
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nfsd_cache_search(struct svc_rqst *rqstp)
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{
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struct svc_cacherep *rp;
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struct hlist_node *hn;
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struct hlist_head *rh;
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__be32 xid = rqstp->rq_xid;
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u32 proto = rqstp->rq_prot,
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vers = rqstp->rq_vers,
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proc = rqstp->rq_proc;
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rh = &cache_hash[request_hash(xid)];
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hlist_for_each_entry(rp, hn, rh, c_hash) {
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if (xid == rp->c_xid && proc == rp->c_proc &&
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proto == rp->c_prot && vers == rp->c_vers &&
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rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) &&
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rpc_get_port(svc_addr(rqstp)) == rpc_get_port((struct sockaddr *)&rp->c_addr))
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return rp;
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}
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return NULL;
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}
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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 grab the oldest unlocked entry off the LRU list.
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* Note that no operation within the loop may sleep.
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*/
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int
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nfsd_cache_lookup(struct svc_rqst *rqstp)
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{
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struct svc_cacherep *rp, *found;
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__be32 xid = rqstp->rq_xid;
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u32 proto = rqstp->rq_prot,
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vers = rqstp->rq_vers,
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proc = rqstp->rq_proc;
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unsigned long age;
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int type = rqstp->rq_cachetype;
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int rtn;
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rqstp->rq_cacherep = NULL;
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if (type == RC_NOCACHE) {
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nfsdstats.rcnocache++;
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return RC_DOIT;
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}
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spin_lock(&cache_lock);
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rtn = RC_DOIT;
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rp = nfsd_cache_search(rqstp);
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if (rp)
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goto found_entry;
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/* Try to use the first entry on the LRU */
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if (!list_empty(&lru_head)) {
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rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
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if (nfsd_cache_entry_expired(rp) ||
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num_drc_entries >= max_drc_entries) {
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lru_put_end(rp);
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prune_cache_entries();
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goto setup_entry;
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}
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}
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spin_unlock(&cache_lock);
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rp = nfsd_reply_cache_alloc();
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if (!rp) {
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dprintk("nfsd: unable to allocate DRC entry!\n");
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return RC_DOIT;
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}
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spin_lock(&cache_lock);
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++num_drc_entries;
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/*
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* Must search again just in case someone inserted one
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* after we dropped the lock above.
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*/
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found = nfsd_cache_search(rqstp);
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if (found) {
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nfsd_reply_cache_free_locked(rp);
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rp = found;
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goto found_entry;
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}
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/*
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* We're keeping the one we just allocated. Are we now over the
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* limit? Prune one off the tip of the LRU in trade for the one we
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* just allocated if so.
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*/
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if (num_drc_entries >= max_drc_entries)
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nfsd_reply_cache_free_locked(list_first_entry(&lru_head,
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struct svc_cacherep, c_lru));
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setup_entry:
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nfsdstats.rcmisses++;
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rqstp->rq_cacherep = rp;
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rp->c_state = RC_INPROG;
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rp->c_xid = xid;
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rp->c_proc = proc;
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rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
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rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
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rp->c_prot = proto;
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rp->c_vers = vers;
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hash_refile(rp);
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lru_put_end(rp);
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/* release any buffer */
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if (rp->c_type == RC_REPLBUFF) {
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kfree(rp->c_replvec.iov_base);
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rp->c_replvec.iov_base = NULL;
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}
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rp->c_type = RC_NOCACHE;
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out:
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spin_unlock(&cache_lock);
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return rtn;
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found_entry:
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nfsdstats.rchits++;
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/* We found a matching entry which is either in progress or done. */
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age = jiffies - rp->c_timestamp;
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lru_put_end(rp);
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rtn = RC_DROPIT;
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/* Request being processed or excessive rexmits */
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if (rp->c_state == RC_INPROG || age < RC_DELAY)
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goto out;
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/* From the hall of fame of impractical attacks:
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* Is this a user who tries to snoop on the cache? */
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rtn = RC_DOIT;
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if (!rqstp->rq_secure && rp->c_secure)
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goto out;
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/* Compose RPC reply header */
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switch (rp->c_type) {
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case RC_NOCACHE:
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break;
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case RC_REPLSTAT:
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svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
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rtn = RC_REPLY;
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break;
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case RC_REPLBUFF:
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if (!nfsd_cache_append(rqstp, &rp->c_replvec))
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goto out; /* should not happen */
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rtn = RC_REPLY;
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break;
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default:
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printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
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nfsd_reply_cache_free_locked(rp);
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}
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goto out;
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}
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/*
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* Update a cache entry. This is called from nfsd_dispatch when
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* the procedure has been executed and the complete reply is in
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* rqstp->rq_res.
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*
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* We're copying around data here rather than swapping buffers because
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* the toplevel loop requires max-sized buffers, which would be a waste
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* of memory for a cache with a max reply size of 100 bytes (diropokres).
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*
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* If we should start to use different types of cache entries tailored
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* specifically for attrstat and fh's, we may save even more space.
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*
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* Also note that a cachetype of RC_NOCACHE can legally be passed when
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* nfsd failed to encode a reply that otherwise would have been cached.
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* In this case, nfsd_cache_update is called with statp == NULL.
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*/
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void
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nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
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{
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struct svc_cacherep *rp = rqstp->rq_cacherep;
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struct kvec *resv = &rqstp->rq_res.head[0], *cachv;
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int len;
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if (!rp)
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return;
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len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
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len >>= 2;
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/* Don't cache excessive amounts of data and XDR failures */
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if (!statp || len > (256 >> 2)) {
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nfsd_reply_cache_free(rp);
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return;
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}
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switch (cachetype) {
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case RC_REPLSTAT:
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if (len != 1)
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printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
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rp->c_replstat = *statp;
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break;
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case RC_REPLBUFF:
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cachv = &rp->c_replvec;
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cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
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if (!cachv->iov_base) {
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nfsd_reply_cache_free(rp);
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return;
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}
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cachv->iov_len = len << 2;
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memcpy(cachv->iov_base, statp, len << 2);
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break;
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case RC_NOCACHE:
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nfsd_reply_cache_free(rp);
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return;
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}
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spin_lock(&cache_lock);
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lru_put_end(rp);
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rp->c_secure = rqstp->rq_secure;
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rp->c_type = cachetype;
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rp->c_state = RC_DONE;
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spin_unlock(&cache_lock);
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return;
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}
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/*
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* Copy cached reply to current reply buffer. Should always fit.
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* FIXME as reply is in a page, we should just attach the page, and
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* keep a refcount....
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*/
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static int
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nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
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{
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struct kvec *vec = &rqstp->rq_res.head[0];
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if (vec->iov_len + data->iov_len > PAGE_SIZE) {
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printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
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data->iov_len);
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return 0;
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}
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memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
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vec->iov_len += data->iov_len;
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return 1;
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}
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