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Eagerly discard attr-list in lfsr_mdir_commit__

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This is an interesting optimization made possible by our attr-lists now
only operating on one mid. We can now discard the entire attr-list based
on if that mid is in the commit's filter range.

Unfortunately, while I had hoped this would lead to more
simplifications, we can't really push this up through many functions:

- While this eager discard works for splits, lfsr_btree_commit can also
  merge, which affects two separate bids. The attrs on these bids need
  to be split over the new btree inner-nodes, so we end up still needing
  filtering in lfsr_rbyd_appendattrs.

  We could move the filtering up into lfsr_btree_commit, but would that
  really gain anything?

- lfsr_mdir_commit_ needs the filter range because we leverage this in
  higher-layers to for lfsr_mdir_commit_ to omit non--1 attrs when
  committing to newly hollow mroots.

  In theory it might still be possible to push this up into
  lfsr_mdir_commit, but we would still need to unconditionally commit
  during mdir splits to append the cksum. This ends up with duplicate
  function calls which ends up annoyingly expensive. Though maybe there
  is a conditional count trick that could avoid this?

At least the code changes are ok:

            code          stack
  before:  33884           2896
  after:   33808 (-0.2%)   2896 (+0.0%)
This commit is contained in:
Christopher Haster
2024-01-25 01:41:53 -06:00
parent 4ebc7d0119
commit b09e933e1e
1 changed files with 12 additions and 28 deletions
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lfs.c
+12 -28
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@@ -5498,16 +5498,18 @@ static int lfsr_mdir_commit__(lfs_t *lfs, lfsr_mdir_t *mdir,
lfsr_smid_t mid, const lfsr_attr_t *attrs, lfs_size_t attr_count) {
// try to append a commit
lfsr_rbyd_t rbyd_ = mdir->rbyd;
lfsr_srid_t rid = lfsr_mid_rid(lfs, mid);
// mark as erased in case of failure
mdir->rbyd.eoff = -1;
for (lfs_size_t i = 0; i < attr_count; i++) {
// don't write tags outside of the requested range
if (rid >= start_rid
// note the use of rid+1 and unsigned comparison here to
// treat end_rid=-1 as "unbounded" in such a way that rid=-1
// is still included
&& (lfs_size_t)(rid + 1) <= (lfs_size_t)end_rid) {
// since we only ever commit to one mid or split, we can ignore the
// entire attr-list if our mid is out of range
lfsr_srid_t rid = lfsr_mid_rid(lfs, mid);
if (rid >= start_rid
// note the use of rid+1 and unsigned comparison here to
// treat end_rid=-1 as "unbounded" in such a way that rid=-1
// is still included
&& (lfs_size_t)(rid + 1) <= (lfs_size_t)end_rid) {
for (lfs_size_t i = 0; i < attr_count; i++) {
// adjust for inserts
if (!lfsr_tag_isgrow(attrs[i].tag) && attrs[i].delta > 0) {
rid -= 1;
@@ -5703,26 +5705,8 @@ static int lfsr_mdir_commit__(lfs_t *lfs, lfsr_mdir_t *mdir,
}
}
// adjust for inserts
if (!lfsr_tag_isgrow(attrs[i].tag) && attrs[i].delta > 0) {
rid += 1;
}
}
// we need to make sure we keep start_rid/end_rid updated with
// weight changes
if (rid < start_rid) {
start_rid += attrs[i].delta;
}
if (rid < end_rid) {
end_rid += attrs[i].delta;
}
// adjust rid
rid += attrs[i].delta;
// adjust for inserts
if (!lfsr_tag_isgrow(attrs[i].tag) && attrs[i].delta > 0) {
rid -= 1;
// adjust rid
rid += attrs[i].delta;
}
}