diff options
Diffstat (limited to 'fs/logfs/gc.c')
| -rw-r--r-- | fs/logfs/gc.c | 730 |
1 files changed, 730 insertions, 0 deletions
diff --git a/fs/logfs/gc.c b/fs/logfs/gc.c new file mode 100644 index 0000000..92949f9 --- /dev/null +++ b/fs/logfs/gc.c @@ -0,0 +1,730 @@ +/* + * fs/logfs/gc.c - garbage collection code + * + * As should be obvious for Linux kernel code, license is GPLv2 + * + * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org> + */ +#include "logfs.h" +#include <linux/sched.h> + +/* + * Wear leveling needs to kick in when the difference between low erase + * counts and high erase counts gets too big. A good value for "too big" + * may be somewhat below 10% of maximum erase count for the device. + * Why not 397, to pick a nice round number with no specific meaning? :) + * + * WL_RATELIMIT is the minimum time between two wear level events. A huge + * number of segments may fulfil the requirements for wear leveling at the + * same time. If that happens we don't want to cause a latency from hell, + * but just gently pick one segment every so often and minimize overhead. + */ +#define WL_DELTA 397 +#define WL_RATELIMIT 100 +#define MAX_OBJ_ALIASES 2600 +#define SCAN_RATIO 512 /* number of scanned segments per gc'd segment */ +#define LIST_SIZE 64 /* base size of candidate lists */ +#define SCAN_ROUNDS 128 /* maximum number of complete medium scans */ +#define SCAN_ROUNDS_HIGH 4 /* maximum number of higher-level scans */ + +static int no_free_segments(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + + return super->s_free_list.count; +} + +/* journal has distance -1, top-most ifile layer distance 0 */ +static u8 root_distance(struct super_block *sb, gc_level_t __gc_level) +{ + struct logfs_super *super = logfs_super(sb); + u8 gc_level = (__force u8)__gc_level; + + switch (gc_level) { + case 0: /* fall through */ + case 1: /* fall through */ + case 2: /* fall through */ + case 3: + /* file data or indirect blocks */ + return super->s_ifile_levels + super->s_iblock_levels - gc_level; + case 6: /* fall through */ + case 7: /* fall through */ + case 8: /* fall through */ + case 9: + /* inode file data or indirect blocks */ + return super->s_ifile_levels - (gc_level - 6); + default: + printk(KERN_ERR"LOGFS: segment of unknown level %x found\n", + gc_level); + WARN_ON(1); + return super->s_ifile_levels + super->s_iblock_levels; + } +} + +static int segment_is_reserved(struct super_block *sb, u32 segno) +{ + struct logfs_super *super = logfs_super(sb); + struct logfs_area *area; + void *reserved; + int i; + + /* Some segments are reserved. Just pretend they were all valid */ + reserved = btree_lookup32(&super->s_reserved_segments, segno); + if (reserved) + return 1; + + /* Currently open segments */ + for_each_area(i) { + area = super->s_area[i]; + if (area->a_is_open && area->a_segno == segno) + return 1; + } + + return 0; +} + +static void logfs_mark_segment_bad(struct super_block *sb, u32 segno) +{ + BUG(); +} + +/* + * Returns the bytes consumed by valid objects in this segment. Object headers + * are counted, the segment header is not. + */ +static u32 logfs_valid_bytes(struct super_block *sb, u32 segno, u32 *ec, + gc_level_t *gc_level) +{ + struct logfs_segment_entry se; + u32 ec_level; + + logfs_get_segment_entry(sb, segno, &se); + if (se.ec_level == cpu_to_be32(BADSEG) || + se.valid == cpu_to_be32(RESERVED)) + return RESERVED; + + ec_level = be32_to_cpu(se.ec_level); + *ec = ec_level >> 4; + *gc_level = GC_LEVEL(ec_level & 0xf); + return be32_to_cpu(se.valid); +} + +static void logfs_cleanse_block(struct super_block *sb, u64 ofs, u64 ino, + u64 bix, gc_level_t gc_level) +{ + struct inode *inode; + int err, cookie; + + inode = logfs_safe_iget(sb, ino, &cookie); + err = logfs_rewrite_block(inode, bix, ofs, gc_level, 0); + BUG_ON(err); + logfs_safe_iput(inode, cookie); +} + +static u32 logfs_gc_segment(struct super_block *sb, u32 segno, u8 dist) +{ + struct logfs_super *super = logfs_super(sb); + struct logfs_segment_header sh; + struct logfs_object_header oh; + u64 ofs, ino, bix; + u32 seg_ofs, logical_segno, cleaned = 0; + int err, len, valid; + gc_level_t gc_level; + + LOGFS_BUG_ON(segment_is_reserved(sb, segno), sb); + + btree_insert32(&super->s_reserved_segments, segno, (void *)1, GFP_NOFS); + err = wbuf_read(sb, dev_ofs(sb, segno, 0), sizeof(sh), &sh); + BUG_ON(err); + gc_level = GC_LEVEL(sh.level); + logical_segno = be32_to_cpu(sh.segno); + if (sh.crc != logfs_crc32(&sh, sizeof(sh), 4)) { + logfs_mark_segment_bad(sb, segno); + cleaned = -1; + goto out; + } + + for (seg_ofs = LOGFS_SEGMENT_HEADERSIZE; + seg_ofs + sizeof(oh) < super->s_segsize; ) { + ofs = dev_ofs(sb, logical_segno, seg_ofs); + err = wbuf_read(sb, dev_ofs(sb, segno, seg_ofs), sizeof(oh), + &oh); + BUG_ON(err); + + if (!memchr_inv(&oh, 0xff, sizeof(oh))) + break; + + if (oh.crc != logfs_crc32(&oh, sizeof(oh) - 4, 4)) { + logfs_mark_segment_bad(sb, segno); + cleaned = super->s_segsize - 1; + goto out; + } + + ino = be64_to_cpu(oh.ino); + bix = be64_to_cpu(oh.bix); + len = sizeof(oh) + be16_to_cpu(oh.len); + valid = logfs_is_valid_block(sb, ofs, ino, bix, gc_level); + if (valid == 1) { + logfs_cleanse_block(sb, ofs, ino, bix, gc_level); + cleaned += len; + } else if (valid == 2) { + /* Will be invalid upon journal commit */ + cleaned += len; + } + seg_ofs += len; + } +out: + btree_remove32(&super->s_reserved_segments, segno); + return cleaned; +} + +static struct gc_candidate *add_list(struct gc_candidate *cand, + struct candidate_list *list) +{ + struct rb_node **p = &list->rb_tree.rb_node; + struct rb_node *parent = NULL; + struct gc_candidate *cur; + int comp; + + cand->list = list; + while (*p) { + parent = *p; + cur = rb_entry(parent, struct gc_candidate, rb_node); + + if (list->sort_by_ec) + comp = cand->erase_count < cur->erase_count; + else + comp = cand->valid < cur->valid; + + if (comp) + p = &parent->rb_left; + else + p = &parent->rb_right; + } + rb_link_node(&cand->rb_node, parent, p); + rb_insert_color(&cand->rb_node, &list->rb_tree); + + if (list->count <= list->maxcount) { + list->count++; + return NULL; + } + cand = rb_entry(rb_last(&list->rb_tree), struct gc_candidate, rb_node); + rb_erase(&cand->rb_node, &list->rb_tree); + cand->list = NULL; + return cand; +} + +static void remove_from_list(struct gc_candidate *cand) +{ + struct candidate_list *list = cand->list; + + rb_erase(&cand->rb_node, &list->rb_tree); + list->count--; +} + +static void free_candidate(struct super_block *sb, struct gc_candidate *cand) +{ + struct logfs_super *super = logfs_super(sb); + + btree_remove32(&super->s_cand_tree, cand->segno); + kfree(cand); +} + +u32 get_best_cand(struct super_block *sb, struct candidate_list *list, u32 *ec) +{ + struct gc_candidate *cand; + u32 segno; + + BUG_ON(list->count == 0); + + cand = rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node); + remove_from_list(cand); + segno = cand->segno; + if (ec) + *ec = cand->erase_count; + free_candidate(sb, cand); + return segno; +} + +/* + * We have several lists to manage segments with. The reserve_list is used to + * deal with bad blocks. We try to keep the best (lowest ec) segments on this + * list. + * The free_list contains free segments for normal usage. It usually gets the + * second pick after the reserve_list. But when the free_list is running short + * it is more important to keep the free_list full than to keep a reserve. + * + * Segments that are not free are put onto a per-level low_list. If we have + * to run garbage collection, we pick a candidate from there. All segments on + * those lists should have at least some free space so GC will make progress. + * + * And last we have the ec_list, which is used to pick segments for wear + * leveling. + * + * If all appropriate lists are full, we simply free the candidate and forget + * about that segment for a while. We have better candidates for each purpose. + */ +static void __add_candidate(struct super_block *sb, struct gc_candidate *cand) +{ + struct logfs_super *super = logfs_super(sb); + u32 full = super->s_segsize - LOGFS_SEGMENT_RESERVE; + + if (cand->valid == 0) { + /* 100% free segments */ + log_gc_noisy("add reserve segment %x (ec %x) at %llx\n", + cand->segno, cand->erase_count, + dev_ofs(sb, cand->segno, 0)); + cand = add_list(cand, &super->s_reserve_list); + if (cand) { + log_gc_noisy("add free segment %x (ec %x) at %llx\n", + cand->segno, cand->erase_count, + dev_ofs(sb, cand->segno, 0)); + cand = add_list(cand, &super->s_free_list); + } + } else { + /* good candidates for Garbage Collection */ + if (cand->valid < full) + cand = add_list(cand, &super->s_low_list[cand->dist]); + /* good candidates for wear leveling, + * segments that were recently written get ignored */ + if (cand) + cand = add_list(cand, &super->s_ec_list); + } + if (cand) + free_candidate(sb, cand); +} + +static int add_candidate(struct super_block *sb, u32 segno, u32 valid, u32 ec, + u8 dist) +{ + struct logfs_super *super = logfs_super(sb); + struct gc_candidate *cand; + + cand = kmalloc(sizeof(*cand), GFP_NOFS); + if (!cand) + return -ENOMEM; + + cand->segno = segno; + cand->valid = valid; + cand->erase_count = ec; + cand->dist = dist; + + btree_insert32(&super->s_cand_tree, segno, cand, GFP_NOFS); + __add_candidate(sb, cand); + return 0; +} + +static void remove_segment_from_lists(struct super_block *sb, u32 segno) +{ + struct logfs_super *super = logfs_super(sb); + struct gc_candidate *cand; + + cand = btree_lookup32(&super->s_cand_tree, segno); + if (cand) { + remove_from_list(cand); + free_candidate(sb, cand); + } +} + +static void scan_segment(struct super_block *sb, u32 segno) +{ + u32 valid, ec = 0; + gc_level_t gc_level = 0; + u8 dist; + + if (segment_is_reserved(sb, segno)) + return; + + remove_segment_from_lists(sb, segno); + valid = logfs_valid_bytes(sb, segno, &ec, &gc_level); + if (valid == RESERVED) + return; + + dist = root_distance(sb, gc_level); + add_candidate(sb, segno, valid, ec, dist); +} + +static struct gc_candidate *first_in_list(struct candidate_list *list) +{ + if (list->count == 0) + return NULL; + return rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node); +} + +/* + * Find the best segment for garbage collection. Main criterion is + * the segment requiring the least effort to clean. Secondary + * criterion is to GC on the lowest level available. + * + * So we search the least effort segment on the lowest level first, + * then move up and pick another segment iff is requires significantly + * less effort. Hence the LOGFS_MAX_OBJECTSIZE in the comparison. + */ +static struct gc_candidate *get_candidate(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + int i, max_dist; + struct gc_candidate *cand = NULL, *this; + + max_dist = min(no_free_segments(sb), LOGFS_NO_AREAS); + + for (i = max_dist; i >= 0; i--) { + this = first_in_list(&super->s_low_list[i]); + if (!this) + continue; + if (!cand) + cand = this; + if (this->valid + LOGFS_MAX_OBJECTSIZE <= cand->valid) + cand = this; + } + return cand; +} + +static int __logfs_gc_once(struct super_block *sb, struct gc_candidate *cand) +{ + struct logfs_super *super = logfs_super(sb); + gc_level_t gc_level; + u32 cleaned, valid, segno, ec; + u8 dist; + + if (!cand) { + log_gc("GC attempted, but no candidate found\n"); + return 0; + } + + segno = cand->segno; + dist = cand->dist; + valid = logfs_valid_bytes(sb, segno, &ec, &gc_level); + free_candidate(sb, cand); + log_gc("GC segment #%02x at %llx, %x required, %x free, %x valid, %llx free\n", + segno, (u64)segno << super->s_segshift, + dist, no_free_segments(sb), valid, + super->s_free_bytes); + cleaned = logfs_gc_segment(sb, segno, dist); + log_gc("GC segment #%02x complete - now %x valid\n", segno, + valid - cleaned); + BUG_ON(cleaned != valid); + return 1; +} + +static int logfs_gc_once(struct super_block *sb) +{ + struct gc_candidate *cand; + + cand = get_candidate(sb); + if (cand) + remove_from_list(cand); + return __logfs_gc_once(sb, cand); +} + +/* returns 1 if a wrap occurs, 0 otherwise */ +static int logfs_scan_some(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + u32 segno; + int i, ret = 0; + + segno = super->s_sweeper; + for (i = SCAN_RATIO; i > 0; i--) { + segno++; + if (segno >= super->s_no_segs) { + segno = 0; + ret = 1; + /* Break out of the loop. We want to read a single + * block from the segment size on next invocation if + * SCAN_RATIO is set to match block size + */ + break; + } + + scan_segment(sb, segno); + } + super->s_sweeper = segno; + return ret; +} + +/* + * In principle, this function should loop forever, looking for GC candidates + * and moving data. LogFS is designed in such a way that this loop is + * guaranteed to terminate. + * + * Limiting the loop to some iterations serves purely to catch cases when + * these guarantees have failed. An actual endless loop is an obvious bug + * and should be reported as such. + */ +static void __logfs_gc_pass(struct super_block *sb, int target) +{ + struct logfs_super *super = logfs_super(sb); + struct logfs_block *block; + int round, progress, last_progress = 0; + + if (no_free_segments(sb) >= target && + super->s_no_object_aliases < MAX_OBJ_ALIASES) + return; + + log_gc("__logfs_gc_pass(%x)\n", target); + for (round = 0; round < SCAN_ROUNDS; ) { + if (no_free_segments(sb) >= target) + goto write_alias; + + /* Sync in-memory state with on-medium state in case they + * diverged */ + logfs_write_anchor(sb); + round += logfs_scan_some(sb); + if (no_free_segments(sb) >= target) + goto write_alias; + progress = logfs_gc_once(sb); + if (progress) + last_progress = round; + else if (round - last_progress > 2) + break; + continue; + + /* + * The goto logic is nasty, I just don't know a better way to + * code it. GC is supposed to ensure two things: + * 1. Enough free segments are available. + * 2. The number of aliases is bounded. + * When 1. is achieved, we take a look at 2. and write back + * some alias-containing blocks, if necessary. However, after + * each such write we need to go back to 1., as writes can + * consume free segments. + */ +write_alias: + if (super->s_no_object_aliases < MAX_OBJ_ALIASES) + return; + if (list_empty(&super->s_object_alias)) { + /* All aliases are still in btree */ + return; + } + log_gc("Write back one alias\n"); + block = list_entry(super->s_object_alias.next, + struct logfs_block, alias_list); + block->ops->write_block(block); + /* + * To round off the nasty goto logic, we reset round here. It + * is a safety-net for GC not making any progress and limited + * to something reasonably small. If incremented it for every + * single alias, the loop could terminate rather quickly. + */ + round = 0; + } + LOGFS_BUG(sb); +} + +static int wl_ratelimit(struct super_block *sb, u64 *next_event) +{ + struct logfs_super *super = logfs_super(sb); + + if (*next_event < super->s_gec) { + *next_event = super->s_gec + WL_RATELIMIT; + return 0; + } + return 1; +} + +static void logfs_wl_pass(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + struct gc_candidate *wl_cand, *free_cand; + + if (wl_ratelimit(sb, &super->s_wl_gec_ostore)) + return; + + wl_cand = first_in_list(&super->s_ec_list); + if (!wl_cand) + return; + free_cand = first_in_list(&super->s_free_list); + if (!free_cand) + return; + + if (wl_cand->erase_count < free_cand->erase_count + WL_DELTA) { + remove_from_list(wl_cand); + __logfs_gc_once(sb, wl_cand); + } +} + +/* + * The journal needs wear leveling as well. But moving the journal is an + * expensive operation so we try to avoid it as much as possible. And if we + * have to do it, we move the whole journal, not individual segments. + * + * Ratelimiting is not strictly necessary here, it mainly serves to avoid the + * calculations. First we check whether moving the journal would be a + * significant improvement. That means that a) the current journal segments + * have more wear than the future journal segments and b) the current journal + * segments have more wear than normal ostore segments. + * Rationale for b) is that we don't have to move the journal if it is aging + * less than the ostore, even if the reserve segments age even less (they are + * excluded from wear leveling, after all). + * Next we check that the superblocks have less wear than the journal. Since + * moving the journal requires writing the superblocks, we have to protect the + * superblocks even more than the journal. + * + * Also we double the acceptable wear difference, compared to ostore wear + * leveling. Journal data is read and rewritten rapidly, comparatively. So + * soft errors have much less time to accumulate and we allow the journal to + * be a bit worse than the ostore. + */ +static void logfs_journal_wl_pass(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + struct gc_candidate *cand; + u32 min_journal_ec = -1, max_reserve_ec = 0; + int i; + + if (wl_ratelimit(sb, &super->s_wl_gec_journal)) + return; + + if (super->s_reserve_list.count < super->s_no_journal_segs) { + /* Reserve is not full enough to move complete journal */ + return; + } + + journal_for_each(i) + if (super->s_journal_seg[i]) + min_journal_ec = min(min_journal_ec, + super->s_journal_ec[i]); + cand = rb_entry(rb_first(&super->s_free_list.rb_tree), + struct gc_candidate, rb_node); + max_reserve_ec = cand->erase_count; + for (i = 0; i < 2; i++) { + struct logfs_segment_entry se; + u32 segno = seg_no(sb, super->s_sb_ofs[i]); + u32 ec; + + logfs_get_segment_entry(sb, segno, &se); + ec = be32_to_cpu(se.ec_level) >> 4; + max_reserve_ec = max(max_reserve_ec, ec); + } + + if (min_journal_ec > max_reserve_ec + 2 * WL_DELTA) { + do_logfs_journal_wl_pass(sb); + } +} + +void logfs_gc_pass(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + + //BUG_ON(mutex_trylock(&logfs_super(sb)->s_w_mutex)); + /* Write journal before free space is getting saturated with dirty + * objects. + */ + if (super->s_dirty_used_bytes + super->s_dirty_free_bytes + + LOGFS_MAX_OBJECTSIZE >= super->s_free_bytes) + logfs_write_anchor(sb); + __logfs_gc_pass(sb, super->s_total_levels); + logfs_wl_pass(sb); + logfs_journal_wl_pass(sb); +} + +static int check_area(struct super_block *sb, int i) +{ + struct logfs_super *super = logfs_super(sb); + struct logfs_area *area = super->s_area[i]; + struct logfs_object_header oh; + u32 segno = area->a_segno; + u32 ofs = area->a_used_bytes; + __be32 crc; + int err; + + if (!area->a_is_open) + return 0; + + for (ofs = area->a_used_bytes; + ofs <= super->s_segsize - sizeof(oh); + ofs += (u32)be16_to_cpu(oh.len) + sizeof(oh)) { + err = wbuf_read(sb, dev_ofs(sb, segno, ofs), sizeof(oh), &oh); + if (err) + return err; + + if (!memchr_inv(&oh, 0xff, sizeof(oh))) + break; + + crc = logfs_crc32(&oh, sizeof(oh) - 4, 4); + if (crc != oh.crc) { + printk(KERN_INFO "interrupted header at %llx\n", + dev_ofs(sb, segno, ofs)); + return 0; + } + } + if (ofs != area->a_used_bytes) { + printk(KERN_INFO "%x bytes unaccounted data found at %llx\n", + ofs - area->a_used_bytes, + dev_ofs(sb, segno, area->a_used_bytes)); + area->a_used_bytes = ofs; + } + return 0; +} + +int logfs_check_areas(struct super_block *sb) +{ + int i, err; + + for_each_area(i) { + err = check_area(sb, i); + if (err) + return err; + } + return 0; +} + +static void logfs_init_candlist(struct candidate_list *list, int maxcount, + int sort_by_ec) +{ + list->count = 0; + list->maxcount = maxcount; + list->sort_by_ec = sort_by_ec; + list->rb_tree = RB_ROOT; +} + +int logfs_init_gc(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + int i; + + btree_init_mempool32(&super->s_cand_tree, super->s_btree_pool); + logfs_init_candlist(&super->s_free_list, LIST_SIZE + SCAN_RATIO, 1); + logfs_init_candlist(&super->s_reserve_list, + super->s_bad_seg_reserve, 1); + for_each_area(i) + logfs_init_candlist(&super->s_low_list[i], LIST_SIZE, 0); + logfs_init_candlist(&super->s_ec_list, LIST_SIZE, 1); + return 0; +} + +static void logfs_cleanup_list(struct super_block *sb, + struct candidate_list *list) +{ + struct gc_candidate *cand; + + while (list->count) { + cand = rb_entry(list->rb_tree.rb_node, struct gc_candidate, + rb_node); + remove_from_list(cand); + free_candidate(sb, cand); + } + BUG_ON(list->rb_tree.rb_node); +} + +void logfs_cleanup_gc(struct super_block *sb) +{ + struct logfs_super *super = logfs_super(sb); + int i; + + if (!super->s_free_list.count) + return; + + /* + * FIXME: The btree may still contain a single empty node. So we + * call the grim visitor to clean up that mess. Btree code should + * do it for us, really. + */ + btree_grim_visitor32(&super->s_cand_tree, 0, NULL); + logfs_cleanup_list(sb, &super->s_free_list); + logfs_cleanup_list(sb, &super->s_reserve_list); + for_each_area(i) + logfs_cleanup_list(sb, &super->s_low_list[i]); + logfs_cleanup_list(sb, &super->s_ec_list); +} |