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 (5 * 1000000)
17 #define CACHE_CLEAN_DELAY (30 * 1000000)
19 /* Filesystem caching and cache coherency. */
21 static void writeback_complete(gpointer a, gpointer i)
23 BlueSkyInode *inode = (BlueSkyInode *)i;
25 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
26 "Writeback for inode %"PRIu64" complete", inode->inum);
28 g_mutex_lock(inode->lock);
30 inode->change_commit = inode->change_pending;
31 if (inode->change_count == inode->change_commit) {
32 /* If inode is no longer dirty... */
33 inode->change_time = 0;
34 inode->change_pending = 0;
37 g_mutex_unlock(inode->lock);
40 /* Drop cached data for a given inode, if it is clean. inode must be locked. */
41 static void drop_caches(BlueSkyInode *inode)
43 if (inode->type == BLUESKY_REGULAR)
44 bluesky_file_drop_cached(inode);
47 static void flushd_inode(gpointer value, gpointer user_data)
49 BlueSkyFS *fs = (BlueSkyFS *)user_data;
51 BlueSkyInode *inode = (BlueSkyInode *)value;
53 g_mutex_lock(inode->lock);
55 if (inode->change_count == inode->change_commit) {
56 uint64_t delay = bluesky_get_current_time() - inode->access_time;
57 if (delay >= CACHE_CLEAN_DELAY) {
60 /* If the only references are the one we hold and the one in the
61 * filesystem inum->inode hash table... First check the refcount
62 * without the lock for speed, but if the check looks good verify
63 * it after taking the filesystem lock. */
64 if (inode->refcount == 2) {
65 g_mutex_lock(fs->lock);
66 if (inode->refcount == 2) {
67 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
68 "Trying to drop inode %"PRIu64" from cache",
70 if (g_hash_table_remove(fs->inodes, &inode->inum))
71 bluesky_inode_unref(inode);
73 g_mutex_unlock(fs->lock);
77 g_mutex_unlock(inode->lock);
78 bluesky_inode_unref(inode);
82 if (inode->change_pending) {
83 /* Waiting for an earlier writeback to finish, so don't start a new
85 g_mutex_unlock(inode->lock);
86 bluesky_inode_unref(inode);
90 uint64_t elapsed = bluesky_get_current_time() - inode->change_time;
91 if (elapsed < WRITEBACK_DELAY) {
92 /* Give a bit more time before starting writeback. */
93 g_mutex_unlock(inode->lock);
94 bluesky_inode_unref(inode);
98 inode->change_pending = inode->change_count;
100 g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
101 "Starting flush of inode %"PRIu64, inode->inum);
103 /* Create a store barrier. All operations part of the writeback will be
104 * added to this barrier, so when the barrier completes we know that the
105 * writeback is finished. */
106 BlueSkyStoreAsync *barrier = bluesky_store_async_new(fs->store);
107 barrier->op = STORE_OP_BARRIER;
109 bluesky_inode_start_sync(inode, barrier);
111 bluesky_store_async_add_notifier(barrier, writeback_complete, inode);
112 bluesky_store_async_submit(barrier);
113 bluesky_store_async_unref(barrier);
115 g_mutex_unlock(inode->lock);
116 bluesky_inode_unref(inode);
119 /* Scan through the cache for dirty data and start flushing it to stable
120 * storage. This does not guarantee that data is committed when it returns.
121 * Instead, this can be called occasionally to ensure that dirty data is
124 * We do not want to hold the filesystem lock while flushing individual inodes,
125 * a that could lead to deadlock. So first scan through the inode table to get
126 * a reference to all inodes, then process that queue of inodes after dropping
127 * the filesystem lock. */
128 static void gather_inodes(gpointer key, gpointer value, gpointer user_data)
130 GSList **list = (GSList **)user_data;
131 *list = g_slist_prepend(*list, value);
132 bluesky_inode_ref((BlueSkyInode *)value);
135 void bluesky_flushd_invoke(BlueSkyFS *fs)
139 g_mutex_lock(fs->lock);
140 g_hash_table_foreach(fs->inodes, gather_inodes, &list);
141 g_mutex_unlock(fs->lock);
143 list = g_slist_reverse(list);
144 g_slist_foreach(list, flushd_inode, fs);