1 /* Blue Sky: File Systems in the Cloud
3 * Copyright (C) 2009 The Regents of the University of California
4 * Written by Michael Vrable <mvrable@cs.ucsd.edu>
14 #include "bluesky-private.h"
16 #define WRITEBACK_DELAY (20 * 1000000)
17 #define CACHE_DROP_DELAY (20 * 1000000)
19 /* Filesystem caching and cache coherency. There are actually a couple of
20 * different tasks that are performed here:
21 * - Forcing data to the log if needed to reclaim memory or simply if the
22 * data has been dirty in memory long enough.
23 * - Writing batches of data to the cloud.
26 static void flushd_dirty_inode(BlueSkyInode *inode)
28 BlueSkyFS *fs = inode->fs;
30 g_mutex_lock(fs->lock);
31 bluesky_list_unlink(&fs->unlogged_list, inode->unlogged_list);
32 inode->unlogged_list = NULL;
33 g_mutex_unlock(fs->lock);
35 /* Inode is clean; nothing to do. */
36 if (inode->change_count == inode->change_commit)
39 if (bluesky_verbose) {
40 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
41 "Starting flush of inode %"PRIu64, inode->inum);
44 bluesky_inode_start_sync(inode);
47 /* Check whether memory usage may have dropped below critical thresholds for
48 * waking up waiting threads. */
49 void flushd_check_wakeup(BlueSkyFS *fs)
51 int dirty = g_atomic_int_get(&fs->cache_dirty);
52 dirty += g_atomic_int_get(&fs->cache_log_dirty);
54 if (dirty <= bluesky_watermark_high_dirty)
55 g_cond_broadcast(fs->flushd_cond);
58 /* Try to flush dirty data to disk, either due to memory pressure or due to
60 static void flushd_dirty(BlueSkyFS *fs)
62 int64_t start_time = bluesky_get_current_time();
63 g_mutex_lock(fs->lock);
67 if (fs->unlogged_list.prev == NULL)
69 inode = fs->unlogged_list.prev->data;
71 if (bluesky_verbose) {
72 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
73 "Considering flushing inode %"PRIu64, inode->inum);
76 /* Stop processing dirty inodes if we both have enough memory available
77 * and the oldest inode is sufficiently new that it need not be flushed
79 uint64_t elapsed = bluesky_get_current_time() - inode->change_time;
80 if (g_atomic_int_get(&fs->cache_dirty) < bluesky_watermark_low_dirty
81 && elapsed < WRITEBACK_DELAY)
83 if (inode->change_time > start_time)
86 bluesky_inode_ref(inode);
88 g_mutex_unlock(fs->lock);
90 g_mutex_lock(inode->lock);
91 flushd_dirty_inode(inode);
92 g_mutex_unlock(inode->lock);
93 bluesky_inode_unref(inode);
95 g_mutex_lock(fs->lock);
96 flushd_check_wakeup(fs);
99 g_cond_broadcast(fs->flushd_cond);
101 g_mutex_unlock(fs->lock);
104 /* Try to flush dirty data to the cloud.
105 * TODO: Rewrite this to work on cloud log items rather than inodes, so we can
106 * better track which logs are fully synchronized to the cloud and can be
107 * garbage collected if needed? */
108 static void flushd_cloud(BlueSkyFS *fs)
110 int64_t start_time = bluesky_get_current_time();
111 g_mutex_lock(fs->lock);
115 if (fs->dirty_list.prev == NULL)
117 inode = fs->dirty_list.prev->data;
119 if (bluesky_verbose) {
120 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
121 "Flushing inode %"PRIu64" to cloud", inode->inum);
124 /* Stop processing dirty inodes if we both have enough memory available
125 * and the oldest inode is sufficiently new that it need not be flushed
127 uint64_t elapsed = bluesky_get_current_time() - inode->change_time;
128 if (g_atomic_int_get(&fs->cache_dirty) < bluesky_watermark_low_dirty
129 && elapsed < WRITEBACK_DELAY)
131 if (inode->change_time > start_time)
134 bluesky_inode_ref(inode);
136 g_mutex_unlock(fs->lock);
138 g_mutex_lock(inode->lock);
139 flushd_dirty_inode(inode);
140 g_mutex_lock(fs->lock);
141 bluesky_list_unlink(&fs->dirty_list, inode->dirty_list);
142 inode->dirty_list = NULL;
143 g_mutex_unlock(fs->lock);
145 BlueSkyCloudLog *log = inode->committed_item;
146 bluesky_cloudlog_ref(log);
147 g_mutex_unlock(inode->lock);
150 bluesky_cloudlog_serialize(log, fs);
151 bluesky_inode_unref(inode);
152 bluesky_cloudlog_unref(log);
154 g_mutex_lock(fs->lock);
157 g_mutex_unlock(fs->lock);
158 bluesky_cloudlog_flush(fs);
161 /* Drop cached data for a given inode, if it is clean. inode must be locked. */
162 static void drop_caches(BlueSkyInode *inode)
164 if (inode->type == BLUESKY_REGULAR)
165 bluesky_file_drop_cached(inode);
168 /* Drop clean data from the cache if needed. Clean data should generally be
169 * memory-mapped from log file or similar, so the kernel can drop this clean
170 * data from memory for us and hence memory management isn't too important.
171 * Mainly, we'll want to drop references to data that hasn't been accessed in a
172 * while so that it is possible to reclaim log segments on disk. */
173 static void flushd_clean(BlueSkyFS *fs)
175 g_mutex_lock(fs->lock);
177 size_t inode_count = g_hash_table_size(fs->inodes);
181 while (inode_count-- > 0) {
183 if (fs->accessed_list.prev == NULL)
185 inode = fs->accessed_list.prev->data;
187 uint64_t elapsed = bluesky_get_current_time() - inode->access_time;
188 if (elapsed < CACHE_DROP_DELAY)
191 if (bluesky_verbose) {
192 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
193 "Considering dropping cached data for inode %"PRIu64,
197 bluesky_inode_ref(inode);
199 g_mutex_unlock(fs->lock);
201 g_mutex_lock(inode->lock);
203 g_mutex_lock(fs->lock);
204 bluesky_list_unlink(&fs->accessed_list, inode->accessed_list);
205 inode->accessed_list = bluesky_list_prepend(&fs->accessed_list, inode);
206 g_mutex_unlock(fs->lock);
210 g_mutex_unlock(inode->lock);
211 bluesky_inode_unref(inode);
213 g_mutex_lock(fs->lock);
216 g_mutex_unlock(fs->lock);
219 /* Run the flush daemon for a single iteration, though if it is already
220 * executing returns immediately. */
221 static gpointer flushd_task(BlueSkyFS *fs)
223 if (!g_mutex_trylock(fs->flushd_lock))
228 g_mutex_unlock(fs->flushd_lock);
233 void bluesky_flushd_invoke(BlueSkyFS *fs)
235 g_thread_create((GThreadFunc)flushd_task, fs, FALSE, NULL);
238 void bluesky_flushd_invoke_conditional(BlueSkyFS *fs)
240 if (g_atomic_int_get(&fs->cache_dirty) < bluesky_watermark_medium_dirty)
243 if (bluesky_verbose) {
244 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
245 "Too much data; invoking flushd: dirty=%d",
246 g_atomic_int_get(&fs->cache_dirty));
249 bluesky_flushd_invoke(fs);
251 /* If the system is under heavy memory pressure, actually delay execution
252 * so the flush daemon can catch up. */
253 while (g_atomic_int_get(&fs->cache_dirty)
254 + g_atomic_int_get(&fs->cache_log_dirty)
255 > bluesky_watermark_high_dirty) {
256 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
257 "Waiting due to memory pressure, dirty=%d + %d",
258 g_atomic_int_get(&fs->cache_dirty),
259 g_atomic_int_get(&fs->cache_log_dirty));
260 g_mutex_lock(fs->lock);
261 g_cond_wait(fs->flushd_cond, fs->lock);
262 g_mutex_unlock(fs->lock);
266 /* Start a perpetually-running thread that flushes the cache occasionally. */
267 static gpointer flushd_thread(BlueSkyFS *fs)
270 bluesky_flushd_invoke(fs);
271 struct timespec delay;
274 nanosleep(&delay, NULL);
280 void bluesky_flushd_thread_launch(BlueSkyFS *fs)
282 g_thread_create((GThreadFunc)flushd_thread, fs, FALSE, NULL);