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Index free extents by order of length

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Allocators store free extents in two items, one sorted by their blkno
position and the other by their precise length.

The length index makes it easy to search for precise extent lengths, but
it makes it hard to search for a large extent within a given blkno
region.  Skipping in the blkno dimension has to be done for every
precise length value.

We don't need that level of precision.  If we index the extents by a
coarser order of the length then we have a fixed number of orders in
which we have to skip in the blkno dimension when searching within a
specific region.

This changes the length item to be stored at the log(8) order of the
length of the extents.  This groups extents into orders that are close
to the human-friendly base 10 orders of magnitude.

With this change the order field in the key no longer stores the precise
extent length.  To preserve the length of the extent we need to use
another field.  The only 64bit field remaining is the first which is a
higher comparision priority than the type.  So we use the highest
comparison priority zone field to differentiate the position and order
indexes and can now use all three 64bit fields in the key.

Finally, we have to be careful when constructing a key to use _next when
searching for a large extent.  Previously keys were relying on the magic
property that building a key from an extent length of 0 ended up at the
key value -0 = 0.  That only worked because we never stored zero length
extents.  We now store zero length orders so we can't use the negative
trick anymore.  We explicitly treat 0 length extents carefully when
building keys and we subtract the order from U64_MAX to store the orders
from largest to smallest.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-05-21 15:25:56 -07:00
parent 0aa6005c99
commit 9de3ae6dcb
4 changed files with 97 additions and 62 deletions
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utils/src/mkfs.c
+14 -8
View File
@@ -57,6 +57,15 @@ static int write_block(int fd, u32 magic, __le64 fsid, u64 seq, u64 blkno,
return 0;
}
/*
* Return the order of the length of a free extent, which we define as
* floor(log_8_(len)): 0..7 = 0, 8..63 = 1, etc.
*/
static u64 free_extent_order(u64 len)
{
return (flsll(len | 1) - 1) / 3;
}
/*
* Write the single btree block that contains the blkno and len indexed
* items to store the given extent, and update the root to point to it.
@@ -72,19 +81,16 @@ static int write_alloc_root(int fd, __le64 fsid,
root->total_len = cpu_to_le64(len);
memset(&key, 0, sizeof(key));
key.sk_zone = SCOUTFS_FREE_EXTENT_ZONE;
key.sk_type = SCOUTFS_FREE_EXTENT_BLKNO_TYPE;
key.skii_ino = cpu_to_le64(SCOUTFS_ROOT_INO);
key.sk_zone = SCOUTFS_FREE_EXTENT_BLKNO_ZONE;
key.skfb_end = cpu_to_le64(start + len - 1);
key.skfb_len = cpu_to_le64(len);
btree_append_item(bt, &key, NULL, 0);
memset(&key, 0, sizeof(key));
key.sk_zone = SCOUTFS_FREE_EXTENT_ZONE;
key.sk_type = SCOUTFS_FREE_EXTENT_LEN_TYPE;
key.skii_ino = cpu_to_le64(SCOUTFS_ROOT_INO);
key.skfl_neglen = cpu_to_le64(-len);
key.skfl_blkno = cpu_to_le64(start);
key.sk_zone = SCOUTFS_FREE_EXTENT_ORDER_ZONE;
key.skfo_revord = cpu_to_le64(U64_MAX - free_extent_order(len));
key.skfo_end = cpu_to_le64(start + len - 1);
key.skfo_len = cpu_to_le64(len);
btree_append_item(bt, &key, NULL, 0);
return write_block(fd, SCOUTFS_BLOCK_MAGIC_BTREE, fsid, seq, blkno,
utils/src/print.c
+5 -5
View File
@@ -362,17 +362,17 @@ static int print_mounted_client_entry(struct scoutfs_key *key, void *val,
static int print_alloc_item(struct scoutfs_key *key, void *val,
unsigned val_len, void *arg)
{
if (key->sk_type == SCOUTFS_FREE_EXTENT_BLKNO_TYPE)
if (key->sk_zone == SCOUTFS_FREE_EXTENT_BLKNO_ZONE)
printf(" free extent: blkno %llu len %llu end %llu\n",
le64_to_cpu(key->skfb_end) -
le64_to_cpu(key->skfb_len) + 1,
le64_to_cpu(key->skfb_len),
le64_to_cpu(key->skfb_end));
else
printf(" free extent: blkno %llu len %llu neglen %lld\n",
le64_to_cpu(key->skfl_blkno),
-le64_to_cpu(key->skfl_neglen),
(long long)le64_to_cpu(key->skfl_neglen));
printf(" free extent: blkno %llu len %llu order %llu\n",
le64_to_cpu(key->skfo_end) - le64_to_cpu(key->skfo_len) + 1,
le64_to_cpu(key->skfo_len),
(long long)(U64_MAX - le64_to_cpu(key->skfo_revord)));
return 0;
}