1542928 - report LMDB's heap memory allocations

Status: NEW

(Toolkit :: Storage, enhancement, P3)

Description

[Myk Melez [:myk] [@mykmelez]]

We should report LMDB's heap memory allocations so they stop showing up as heap-unclassified in about:memory, per https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Memory_reporting.

The malloc_size_of crate (https://searchfox.org/mozilla-central/source/servo/components/malloc_size_of/lib.rs) may be useful for this. Here's an example that implements its MallocSizeOf trait by calling through to a C++ implementation:

https://searchfox.org/mozilla-central/rev/8d78f219702286c873860f39f9ed78bad1a6d062/servo/components/style/values/computed/font.rs#199-207

Perhaps we could implement this in rkv/lmdb-rs behind a "gecko" feature flag, like the style and style_traits crates.