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roots: separate crawl sizes into bytes and items

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Number of items should be low enough that we don't have too many stale
items, but high enough to amortize system call overhead to a reasonable
ratio.

Number of bytes should be constant:  one worst-case metadata page (the
btrfs limit is 64K, though 16K is much more common) so that we always
have enough space for one worst-case item; otherwise, we get EOVERFLOW
if we set the number of items too low and there's a big item in the tree,
and we can't make further progress.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2020-11-12 12:10:29 -05:00
parent d332616eff
commit de6282c6cd
2 changed files with 6 additions and 3 deletions
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4
src/bees-roots.cc
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@ -995,7 +995,7 @@ BeesCrawl::fetch_extents()
Timer crawl_timer;
BtrfsIoctlSearchKey sk(BEES_MAX_CRAWL_SIZE * (sizeof(btrfs_file_extent_item) + sizeof(btrfs_ioctl_search_header)));
BtrfsIoctlSearchKey sk(BEES_MAX_CRAWL_BYTES);
sk.tree_id = old_state.m_root;
sk.min_objectid = old_state.m_objectid;
sk.min_type = sk.max_type = BTRFS_EXTENT_DATA_KEY;
@ -1006,7 +1006,7 @@ BeesCrawl::fetch_extents()
// the filesystem while slowing us down.
// sk.max_transid = old_state.m_max_transid;
sk.max_transid = numeric_limits<uint64_t>::max();
sk.nr_items = BEES_MAX_CRAWL_SIZE;
sk.nr_items = BEES_MAX_CRAWL_ITEMS;
// Lock in the old state
set_state(old_state);

5
src/bees.h
View File

@ -101,7 +101,10 @@ const double BEES_HASH_TABLE_ANALYZE_INTERVAL = BEES_STATS_INTERVAL;
const size_t BEES_MAX_QUEUE_SIZE = 128;
// Read this many items at a time in SEARCHv2
const size_t BEES_MAX_CRAWL_SIZE = 1024;
const size_t BEES_MAX_CRAWL_ITEMS = 8;
// Read this many bytes at a time in SEARCHv2 (one maximum-sized metadata page)
const size_t BEES_MAX_CRAWL_BYTES = 64 * 1024;
// Insert this many items before switching to a new subvol
const size_t BEES_MAX_CRAWL_BATCH = 128;