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Reverted lazy encoding for branch attrs

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This was the one lazy attr that did _not_ save us code or stack, and in
fact hurt us a bit. Fortunately our lazy attr scheme still allows for
eager attr encoding, so we can revert just this one attr.

The reason is because we need to keep the children branches around as we
recursively commit up the btree, and, even assuming worst-case, the
branch encoding takes up way less RAM than an active rbyd.

Compare for yourself:

  in-RAM rbyd:         on-disk branch:
  .---+---+---+---.    .---+- -+- -+- -+- -.
  |     weight    |    | block             |
  +---+---+---+---+    +---+- -+- -+- -+- -'
  |     blocks    |    | trunk         |
  +               +    +---+- -+- -+- -+
  |               |    |     cksum     |
  +---+---+---+---+    '---+---+---+---'
  |s|   trunk     |
  +---+---+---+---+
  |p|    eoff     |
  +---+---+---+---+
  |     cksum     |
  '---+---+---+---'
  '-------.-------'    '---------.---------'
       24 bytes               13 bytes

Note we also don't have to care about alignment issues when passing
around the raw encoding.

There may also be something going on with the compiler assuming all
lfsr_rbyd_t pointers may alias, but it's a bit hard to tell.

Saves both code and stack:

           code          stack          ctx
  before: 35592           2472          636
  after:  35552 (-0.1%)   2440 (-1.3%)  636 (+0.0%)
This commit is contained in:
Christopher Haster
2025-02-11 02:00:44 -06:00
parent 3b3b8eab03
commit eaf24b81be
1 changed files with 21 additions and 27 deletions
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lfs.c
+21 -27
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@@ -3363,8 +3363,6 @@ static lfsr_data_t lfsr_data_frombtree(const lfsr_btree_t *btree,
uint8_t buffer[static LFSR_BTREE_DSIZE]);
static lfsr_data_t lfsr_data_frommptr(const lfs_block_t mptr[static 2],
uint8_t buffer[static LFSR_MPTR_DSIZE]);
static lfsr_data_t lfsr_data_frombranch(const lfsr_rbyd_t *branch,
uint8_t buffer[static LFSR_BRANCH_DSIZE]);
static int lfsr_rbyd_appendrattr_(lfs_t *lfs, lfsr_rbyd_t *rbyd,
lfsr_rattr_t rattr) {
@@ -3398,9 +3396,7 @@ static int lfsr_rbyd_appendrattr_(lfs_t *lfs, lfsr_rbyd_t *rbyd,
LFSR_BTREE_DSIZE,
LFS_MAX(
LFSR_MPTR_DSIZE,
LFS_MAX(
LFSR_BRANCH_DSIZE,
LFSR_ECKSUM_DSIZE))))))))];
LFSR_ECKSUM_DSIZE)))))))];
struct {
lfsr_data_t datas[2];
uint8_t buf[LFSR_LEB128_DSIZE];
@@ -3489,15 +3485,6 @@ static int lfsr_rbyd_appendrattr_(lfs_t *lfs, lfsr_rbyd_t *rbyd,
data_count = size;
break;
// branch?
case LFSR_TAG_BRANCH:;
case LFSR_TAG_SHRUB | LFSR_TAG_BRANCH:;
data = lfsr_data_frombranch(rattr.u.etc, ctx.u.buf);
size = lfsr_data_size(data);
datas = ctx.u.buf;
data_count = size;
break;
// ecksum?
case LFSR_TAG_ECKSUM:;
data = lfsr_data_fromecksum(rattr.u.etc, ctx.u.buf);
@@ -5334,7 +5321,7 @@ static int lfsr_btree_parent(lfs_t *lfs, const lfsr_btree_t *btree,
typedef struct lfsr_bctx {
lfsr_rattr_t rattrs[4];
lfsr_data_t split_name;
lfsr_rbyd_t branches[2];
uint8_t buf[2*LFSR_BRANCH_DSIZE];
} lfsr_bctx_t;
// core btree algorithm
@@ -5723,14 +5710,16 @@ static int lfsr_btree_commit__(lfs_t *lfs, lfsr_btree_t *btree,
rattr_count_ = 0;
// new root?
if (!lfsr_rbyd_trunk(&parent)) {
bctx->branches[0] = rbyd__;
lfsr_data_t branch_l = lfsr_data_frombranch(
&rbyd__, &bctx->buf[0*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, +rbyd__.weight,
&bctx->branches[0], LFSR_BRANCH_DSIZE);
bctx->branches[1] = sibling;
branch_l.u.buffer, lfsr_data_size(branch_l));
lfsr_data_t branch_r = lfsr_data_frombranch(
&sibling, &bctx->buf[1*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, +sibling.weight,
&bctx->branches[1], LFSR_BRANCH_DSIZE);
branch_r.u.buffer, lfsr_data_size(branch_r));
if (lfsr_tag_suptype(split_tag) == LFSR_TAG_NAME) {
bctx->rattrs[rattr_count_++] = LFSR_RATTR_DATA(
LFSR_TAG_NAME, 0,
@@ -5739,19 +5728,21 @@ static int lfsr_btree_commit__(lfs_t *lfs, lfsr_btree_t *btree,
// split root?
} else {
bid_ -= pid - (rbyd_.weight-1);
bctx->branches[0] = rbyd__;
lfsr_data_t branch_l = lfsr_data_frombranch(
&rbyd__, &bctx->buf[0*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, 0,
&bctx->branches[0], LFSR_BRANCH_DSIZE);
branch_l.u.buffer, lfsr_data_size(branch_l));
if (rbyd__.weight != rbyd_.weight) {
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_GROW, -rbyd_.weight + rbyd__.weight,
NULL, 0);
}
bctx->branches[1] = sibling;
lfsr_data_t branch_r = lfsr_data_frombranch(
&sibling, &bctx->buf[1*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, +sibling.weight,
&bctx->branches[1], LFSR_BRANCH_DSIZE);
branch_r.u.buffer, lfsr_data_size(branch_r));
if (lfsr_tag_suptype(split_tag) == LFSR_TAG_NAME) {
bctx->rattrs[rattr_count_++] = LFSR_RATTR_DATA(
LFSR_TAG_NAME, 0,
@@ -5829,13 +5820,15 @@ static int lfsr_btree_commit__(lfs_t *lfs, lfsr_btree_t *btree,
// prepare commit to parent, tail recursing upwards
LFS_ASSERT(rbyd__.weight > 0);
rattr_count_ = 0;
// build attr list
bid_ -= pid - (rbyd_.weight-1);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_RM, -sibling.weight, NULL, 0);
bctx->branches[0] = rbyd__;
lfsr_data_t branch = lfsr_data_frombranch(
&rbyd__, &bctx->buf[0*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, 0,
&bctx->branches[0], LFSR_BRANCH_DSIZE);
branch.u.buffer, lfsr_data_size(branch));
if (rbyd__.weight != rbyd_.weight) {
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_GROW, -rbyd_.weight + rbyd__.weight,
@@ -5873,10 +5866,11 @@ static int lfsr_btree_commit__(lfs_t *lfs, lfsr_btree_t *btree,
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_RM, -rbyd_.weight, NULL, 0);
} else {
bctx->branches[0] = rbyd__;
lfsr_data_t branch = lfsr_data_frombranch(
&rbyd__, &bctx->buf[0*LFSR_BRANCH_DSIZE]);
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_BRANCH, 0,
&bctx->branches[0], LFSR_BRANCH_DSIZE);
branch.u.buffer, lfsr_data_size(branch));
if (rbyd__.weight != rbyd_.weight) {
bctx->rattrs[rattr_count_++] = LFSR_RATTR(
LFSR_TAG_GROW, -rbyd_.weight + rbyd__.weight,