[ur] optimize align allocation in DisjointPool #625
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| // so the bucket will be properly aligned. | ||
| AlignedSize = (Size > 1) ? AlignUp(Size, Alignment) : Alignment; | ||
| } else { | ||
| AlignedSize = Size + Alignment - 1; |
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I'm not exactly sure what's the purpose of adding alignment to the size here? Can't we just always AlignUp? This should always be called with size being a multiple of alignment anyway (which is what AlignUp enforces).
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Consider a case where size = alignment = 1MB. Slabs are only aligned to ProviderMinPageSize (let's say 4KB) so aligning up to Alignment is not enough (and we're allocating from Slabs up to 2GB allocations).
When we're allocating directly from the memory provider (line 775) we don't need to do any adjustments, we just leave it to the provider.
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This is potentially very wasteful if there are many such allocations. We just need to create a bucket that offsets the beginning of the slab. Or we can just create an aligned slab, which should be doable if alignment is page-aligned. And even if it's not, at worst we'd waste 4kb per slab.
Let's leave it as-is for now, but might be worth investigating whether this is a common case and worth optimizing.
But please add a comment here explaining this.
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Done. Just one clarification - the 2GB I mentioned is actually just the upper limit for poolableSize. By default poolableSize is around a few MB (so allocation bigger than a few MBs will bypass the pooling).
Do not increase size by Alignment - 1 if the requested Alignment is smaller or equal to coarse-grain allocation alignemnt - in such case, Bucket for the allocation will already be properly aligned.
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Do not increase size by Alignment - 1 if the requested Alignment is smaller or equal to coarse-grain allocation alignemnt - in such case, Bucket for the allocation will already be properly aligned.