(2.12) Elastic pointers in the filestore write-through cache #7180
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Want to investigate some flaking tests first before review. |
| // The reference mb.cache shouldn't have changed ordinarily, but | ||
| // stash it away into the weak pointer again just in case. | ||
| mb.ecache.Set(mb.cache) | ||
| mb.cache = nil |
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We have two levels in the cache, the indexing and the data itself. Both IIRC are under mb.cache but they have different lifetimes under normal operations. This seems to undo that?
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They're still held in the ecache until it is GC'd (and for that there would need to be no strong references left too), but if that happens, we'll just reload the block and re-index it the next time we need to.
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fss is held outside this scope. Not sure if we want this extended to that in a follow on PR or not.
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Yep, I can look into it as a follow-up for sure.
| mbcache.wp = 0 | ||
| } | ||
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| mb.ecache.Weaken() |
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This a no-op if line 5557 excuted?
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Yes, it would have no effect in that case.
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| "weak" | ||
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| func Make[T any](ptr *T) *Pointer[T] { |
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Seems this is unused, can it be removed?
| // can reuse. | ||
| if mb.cacheAlreadyLoaded() { | ||
| return | ||
| } |
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mb.cache is initialized below, but then mb.ecache is not set to it?
This would probably lead to the mb.ecache.Strengthen() call not actually doing work.
Signed-off-by: Neil Twigg <[email protected]>
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This PR modifies the write-through cache in the filestore to use elastic pointers. Elastic pointers are weak by default and can be reclaimed by the GC under pressure, but can be strengthened when there are pending writes for a block. Once the flush has completed, we weaken the cache again.
There are now two cache references within each
msgBlock:mb.ecache: The elastic pointer, populated when the cache is set up and only reset back tonileither by the GC or whenclearCacheis calledmb.cache: Left asnilby default, populated with a strong reference frommb.ecachewhen we need to use the cache, and then reset back tonilafter we're done with itThis PR replaces and therefore closes #7097.
Signed-off-by: Neil Twigg [email protected]