Avoid holding the keg lock for longer than necessary. This helps ensure
that trimming the zone doesn't block allocations for longer than really
needed. If a zone's bucket list has recently been drained and we are
draining the keg, it is likely that allocations will block until
keg_drain() has emptied the free slab list, and that may take a long
time.
Details
Details
- Reviewers
rlibby jeff - Commits
- rS357776: Reduce lock hold time in keg_drain().
Diff Detail
Diff Detail
- Repository
- rS FreeBSD src repository - subversion
- Lint
Lint Not Applicable - Unit
Tests Not Applicable
Event Timeline
| sys/vm/uma_core.c | ||
|---|---|---|
| 1273 ↗ | (On Diff #67849) | You can delete this check now. |
| 1283–1284 ↗ | (On Diff #67849) | This is outside the lock, so we don't really care, but I think there's no particular reason to maintain the list here vs abandoning it as we iterate with LIST_FOREACH_SAFE. Additionally, only this list maintenance writes the slab header on destruction here. |
| 3426–3430 ↗ | (On Diff #67849) | It might be useful to leave a comment explaining that we know that slab was on the partial list, and NOT the free list (even if it is totally free, and so we aren't missing a ud_free_slabs-- here), and maybe to leave a similar comment about the slab returned by keg_fetch_slab. |
Comment Actions
Apply Ryan's feedback:
- Remove an unneeded check in keg_drain().
- Avoid unnecessarily dirtying slab headers in keg_drain().
- Add some comments to explain how we know that no extra ud_free_slabs manipulation is needed.
| sys/vm/uma_core.c | ||
|---|---|---|
| 4648–4651 ↗ | (On Diff #67867) | Let's make this sequence an inline since it's now three statements that are repeated in multiple places. |
| sys/vm/uma_int.h | ||
| 330 ↗ | (On Diff #67867) | I'm I correct in there being 32bit left before we spill to a new line? |
| sys/vm/uma_int.h | ||
|---|---|---|
| 330 ↗ | (On Diff #67867) | No, ud_lock is in its own cache line and struct slabhead is a single pointer, so there is still a lot of padding left over. |