1 /* 2 * This file is part of UBIFS. 3 * 4 * Copyright (C) 2006-2008 Nokia Corporation. 5 * 6 * This program is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 as published by 8 * the Free Software Foundation. 9 * 10 * This program is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 13 * more details. 14 * 15 * You should have received a copy of the GNU General Public License along with 16 * this program; if not, write to the Free Software Foundation, Inc., 51 17 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA 18 * 19 * Authors: Artem Bityutskiy (Битюцкий Артём) 20 * Adrian Hunter 21 */ 22 23 /* 24 * This file implements UBIFS shrinker which evicts clean znodes from the TNC 25 * tree when Linux VM needs more RAM. 26 * 27 * We do not implement any LRU lists to find oldest znodes to free because it 28 * would add additional overhead to the file system fast paths. So the shrinker 29 * just walks the TNC tree when searching for znodes to free. 30 * 31 * If the root of a TNC sub-tree is clean and old enough, then the children are 32 * also clean and old enough. So the shrinker walks the TNC in level order and 33 * dumps entire sub-trees. 34 * 35 * The age of znodes is just the time-stamp when they were last looked at. 36 * The current shrinker first tries to evict old znodes, then young ones. 37 * 38 * Since the shrinker is global, it has to protect against races with FS 39 * un-mounts, which is done by the 'ubifs_infos_lock' and 'c->umount_mutex'. 40 */ 41 42 #include "ubifs.h" 43 44 /* List of all UBIFS file-system instances */ 45 LIST_HEAD(ubifs_infos); 46 47 /* 48 * We number each shrinker run and record the number on the ubifs_info structure 49 * so that we can easily work out which ubifs_info structures have already been 50 * done by the current run. 51 */ 52 static unsigned int shrinker_run_no; 53 54 /* Protects 'ubifs_infos' list */ 55 DEFINE_SPINLOCK(ubifs_infos_lock); 56 57 /* Global clean znode counter (for all mounted UBIFS instances) */ 58 atomic_long_t ubifs_clean_zn_cnt; 59 60 /** 61 * shrink_tnc - shrink TNC tree. 62 * @c: UBIFS file-system description object 63 * @nr: number of znodes to free 64 * @age: the age of znodes to free 65 * @contention: if any contention, this is set to %1 66 * 67 * This function traverses TNC tree and frees clean znodes. It does not free 68 * clean znodes which younger then @age. Returns number of freed znodes. 69 */ 70 static int shrink_tnc(struct ubifs_info *c, int nr, int age, int *contention) 71 { 72 int total_freed = 0; 73 struct ubifs_znode *znode, *zprev; 74 int time = get_seconds(); 75 76 ubifs_assert(mutex_is_locked(&c->umount_mutex)); 77 ubifs_assert(mutex_is_locked(&c->tnc_mutex)); 78 79 if (!c->zroot.znode || atomic_long_read(&c->clean_zn_cnt) == 0) 80 return 0; 81 82 /* 83 * Traverse the TNC tree in levelorder manner, so that it is possible 84 * to destroy large sub-trees. Indeed, if a znode is old, then all its 85 * children are older or of the same age. 86 * 87 * Note, we are holding 'c->tnc_mutex', so we do not have to lock the 88 * 'c->space_lock' when _reading_ 'c->clean_zn_cnt', because it is 89 * changed only when the 'c->tnc_mutex' is held. 90 */ 91 zprev = NULL; 92 znode = ubifs_tnc_levelorder_next(c->zroot.znode, NULL); 93 while (znode && total_freed < nr && 94 atomic_long_read(&c->clean_zn_cnt) > 0) { 95 int freed; 96 97 /* 98 * If the znode is clean, but it is in the 'c->cnext' list, this 99 * means that this znode has just been written to flash as a 100 * part of commit and was marked clean. They will be removed 101 * from the list at end commit. We cannot change the list, 102 * because it is not protected by any mutex (design decision to 103 * make commit really independent and parallel to main I/O). So 104 * we just skip these znodes. 105 * 106 * Note, the 'clean_zn_cnt' counters are not updated until 107 * after the commit, so the UBIFS shrinker does not report 108 * the znodes which are in the 'c->cnext' list as freeable. 109 * 110 * Also note, if the root of a sub-tree is not in 'c->cnext', 111 * then the whole sub-tree is not in 'c->cnext' as well, so it 112 * is safe to dump whole sub-tree. 113 */ 114 115 if (znode->cnext) { 116 /* 117 * Very soon these znodes will be removed from the list 118 * and become freeable. 119 */ 120 *contention = 1; 121 } else if (!ubifs_zn_dirty(znode) && 122 abs(time - znode->time) >= age) { 123 if (znode->parent) 124 znode->parent->zbranch[znode->iip].znode = NULL; 125 else 126 c->zroot.znode = NULL; 127 128 freed = ubifs_destroy_tnc_subtree(znode); 129 atomic_long_sub(freed, &ubifs_clean_zn_cnt); 130 atomic_long_sub(freed, &c->clean_zn_cnt); 131 ubifs_assert(atomic_long_read(&c->clean_zn_cnt) >= 0); 132 total_freed += freed; 133 znode = zprev; 134 } 135 136 if (unlikely(!c->zroot.znode)) 137 break; 138 139 zprev = znode; 140 znode = ubifs_tnc_levelorder_next(c->zroot.znode, znode); 141 cond_resched(); 142 } 143 144 return total_freed; 145 } 146 147 /** 148 * shrink_tnc_trees - shrink UBIFS TNC trees. 149 * @nr: number of znodes to free 150 * @age: the age of znodes to free 151 * @contention: if any contention, this is set to %1 152 * 153 * This function walks the list of mounted UBIFS file-systems and frees clean 154 * znodes which are older than @age, until at least @nr znodes are freed. 155 * Returns the number of freed znodes. 156 */ 157 static int shrink_tnc_trees(int nr, int age, int *contention) 158 { 159 struct ubifs_info *c; 160 struct list_head *p; 161 unsigned int run_no; 162 int freed = 0; 163 164 spin_lock(&ubifs_infos_lock); 165 do { 166 run_no = ++shrinker_run_no; 167 } while (run_no == 0); 168 /* Iterate over all mounted UBIFS file-systems and try to shrink them */ 169 p = ubifs_infos.next; 170 while (p != &ubifs_infos) { 171 c = list_entry(p, struct ubifs_info, infos_list); 172 /* 173 * We move the ones we do to the end of the list, so we stop 174 * when we see one we have already done. 175 */ 176 if (c->shrinker_run_no == run_no) 177 break; 178 if (!mutex_trylock(&c->umount_mutex)) { 179 /* Some un-mount is in progress, try next FS */ 180 *contention = 1; 181 p = p->next; 182 continue; 183 } 184 /* 185 * We're holding 'c->umount_mutex', so the file-system won't go 186 * away. 187 */ 188 if (!mutex_trylock(&c->tnc_mutex)) { 189 mutex_unlock(&c->umount_mutex); 190 *contention = 1; 191 p = p->next; 192 continue; 193 } 194 spin_unlock(&ubifs_infos_lock); 195 /* 196 * OK, now we have TNC locked, the file-system cannot go away - 197 * it is safe to reap the cache. 198 */ 199 c->shrinker_run_no = run_no; 200 freed += shrink_tnc(c, nr, age, contention); 201 mutex_unlock(&c->tnc_mutex); 202 spin_lock(&ubifs_infos_lock); 203 /* Get the next list element before we move this one */ 204 p = p->next; 205 /* 206 * Move this one to the end of the list to provide some 207 * fairness. 208 */ 209 list_move_tail(&c->infos_list, &ubifs_infos); 210 mutex_unlock(&c->umount_mutex); 211 if (freed >= nr) 212 break; 213 } 214 spin_unlock(&ubifs_infos_lock); 215 return freed; 216 } 217 218 /** 219 * kick_a_thread - kick a background thread to start commit. 220 * 221 * This function kicks a background thread to start background commit. Returns 222 * %-1 if a thread was kicked or there is another reason to assume the memory 223 * will soon be freed or become freeable. If there are no dirty znodes, returns 224 * %0. 225 */ 226 static int kick_a_thread(void) 227 { 228 int i; 229 struct ubifs_info *c; 230 231 /* 232 * Iterate over all mounted UBIFS file-systems and find out if there is 233 * already an ongoing commit operation there. If no, then iterate for 234 * the second time and initiate background commit. 235 */ 236 spin_lock(&ubifs_infos_lock); 237 for (i = 0; i < 2; i++) { 238 list_for_each_entry(c, &ubifs_infos, infos_list) { 239 long dirty_zn_cnt; 240 241 if (!mutex_trylock(&c->umount_mutex)) { 242 /* 243 * Some un-mount is in progress, it will 244 * certainly free memory, so just return. 245 */ 246 spin_unlock(&ubifs_infos_lock); 247 return -1; 248 } 249 250 dirty_zn_cnt = atomic_long_read(&c->dirty_zn_cnt); 251 252 if (!dirty_zn_cnt || c->cmt_state == COMMIT_BROKEN || 253 c->ro_mount || c->ro_error) { 254 mutex_unlock(&c->umount_mutex); 255 continue; 256 } 257 258 if (c->cmt_state != COMMIT_RESTING) { 259 spin_unlock(&ubifs_infos_lock); 260 mutex_unlock(&c->umount_mutex); 261 return -1; 262 } 263 264 if (i == 1) { 265 list_move_tail(&c->infos_list, &ubifs_infos); 266 spin_unlock(&ubifs_infos_lock); 267 268 ubifs_request_bg_commit(c); 269 mutex_unlock(&c->umount_mutex); 270 return -1; 271 } 272 mutex_unlock(&c->umount_mutex); 273 } 274 } 275 spin_unlock(&ubifs_infos_lock); 276 277 return 0; 278 } 279 280 int ubifs_shrinker(struct shrinker *shrink, int nr, gfp_t gfp_mask) 281 { 282 int freed, contention = 0; 283 long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt); 284 285 if (nr == 0) 286 return clean_zn_cnt; 287 288 if (!clean_zn_cnt) { 289 /* 290 * No clean znodes, nothing to reap. All we can do in this case 291 * is to kick background threads to start commit, which will 292 * probably make clean znodes which, in turn, will be freeable. 293 * And we return -1 which means will make VM call us again 294 * later. 295 */ 296 dbg_tnc("no clean znodes, kick a thread"); 297 return kick_a_thread(); 298 } 299 300 freed = shrink_tnc_trees(nr, OLD_ZNODE_AGE, &contention); 301 if (freed >= nr) 302 goto out; 303 304 dbg_tnc("not enough old znodes, try to free young ones"); 305 freed += shrink_tnc_trees(nr - freed, YOUNG_ZNODE_AGE, &contention); 306 if (freed >= nr) 307 goto out; 308 309 dbg_tnc("not enough young znodes, free all"); 310 freed += shrink_tnc_trees(nr - freed, 0, &contention); 311 312 if (!freed && contention) { 313 dbg_tnc("freed nothing, but contention"); 314 return -1; 315 } 316 317 out: 318 dbg_tnc("%d znodes were freed, requested %d", freed, nr); 319 return freed; 320 } 321