fscache: Implement simple cookie state machine

Implement a very simple cookie state machine to handle lookup, invalidation, withdrawal, relinquishment and, to be added later, commit on LRU discard. Three cache methods are provided: ->lookup_cookie() to look up and, if necessary, create a data storage object; ->withdraw_cookie() to free the resources associated with that object and potentially delete it; and ->prepare_to_write(), to do prepare for changes to the cached data to be modified locally. Changes ======= ver #3: - Fix a race between LRU discard and relinquishment whereby the former would override the latter and thus the latter would never happen[1]. ver #2: - Don't hold n_accesses elevated whilst cache is bound to a cookie, but rather add a flag that prevents the state machine from being queued when n_accesses reaches 0.

David Howells committed 5 years ago

Commit 5d00e421 parent 29f18e73 files · +300 −44Browse files

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include/linux/fscache-cache.h +25 −2
include/trace/events/fscache.h +4 −0

include/linux/fscache-cache.h+25−2

@@ -57,6 +57,15 @@ struct fscache_cache_ops { · 56 unmodified lines
57	57
58	58	/* Free the cache's data attached to a volume */
59	59	void (free_volume)(struct fscache_volume volume);
	60	+
	61	+ /* Look up a cookie in the cache */
	62	+ bool (lookup_cookie)(struct fscache_cookie cookie);
	63	+
	64	+ /* Withdraw an object without any cookie access counts held */
	65	+ void (withdraw_cookie)(struct fscache_cookie cookie);
	66	+
	67	+ /* Prepare to write to a live cache object */
	68	+ void (prepare_to_write)(struct fscache_cookie cookie);
60	69	};
61	70
62	71	extern struct workqueue_struct *fscache_wq;
@@ -72,6 +81,7 @@ extern int fscache_add_cache(struct fscache_cache *cache, · 9 unmodified lines
72	81	void *cache_priv);
73	82	extern void fscache_withdraw_cache(struct fscache_cache *cache);
74	83	extern void fscache_withdraw_volume(struct fscache_volume *volume);
	84	+extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);
75	85
76	86	extern void fscache_io_error(struct fscache_cache *cache);
77	87
@@ -85,8 +95,21 @@ extern void fscache_put_cookie(struct fscache_cookie *cookie, · 7 unmodified lines
85	95	enum fscache_cookie_trace where);
86	96	extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
87	97	enum fscache_access_trace why);
88		−extern void fscache_set_cookie_state(struct fscache_cookie *cookie,
89		− enum fscache_cookie_state state);
	98	+extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
	99	+extern void fscache_caching_failed(struct fscache_cookie *cookie);
	100	+
	101	+/**
	102	+ * fscache_cookie_state - Read the state of a cookie
	103	+ * @cookie: The cookie to query
	104	+ *
	105	+ * Get the state of a cookie, imposing an ordering between the cookie contents
	106	+ * and the state value. Paired with fscache_set_cookie_state().
	107	+ */
	108	+static inline
	109	+enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
	110	+{
	111	+ return smp_load_acquire(&cookie->state);
	112	+}
90	113
91	114	/**
92	115	* fscache_get_key - Get a pointer to the cookie key

include/trace/events/fscache.h+4−0

@@ -68,6 +68,8 @@ enum fscache_access_trace { · 67 unmodified lines
68	68	fscache_access_acquire_volume_end,
69	69	fscache_access_cache_pin,
70	70	fscache_access_cache_unpin,
	71	+ fscache_access_lookup_cookie_end,
	72	+ fscache_access_lookup_cookie_end_failed,
71	73	fscache_access_relinquish_volume,
72	74	fscache_access_relinquish_volume_end,
73	75	fscache_access_unlive,
@@ -124,6 +126,8 @@ enum fscache_access_trace { · 50 unmodified lines
124	126	EM(fscache_access_acquire_volume_end, "END acq_vol") \
125	127	EM(fscache_access_cache_pin, "PIN cache ") \
126	128	EM(fscache_access_cache_unpin, "UNPIN cache ") \
	129	+ EM(fscache_access_lookup_cookie_end, "END lookup ") \
	130	+ EM(fscache_access_lookup_cookie_end_failed,"END lookupf") \
127	131	EM(fscache_access_relinquish_volume, "BEGIN rlq_vol") \
128	132	EM(fscache_access_relinquish_volume_end,"END rlq_vol") \
129	133	E_(fscache_access_unlive, "END unlive ")

fscache: Implement simple cookie state machine

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