docs(audits): Vec<FileEntry> vs upstream pool allocator (#1050)#3833
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Document the container-level RSS gap between oc-rsync's Vec<FileEntry> + segmented file lists and upstream rsync's pool_alloc.c slab arena. Quantify Vec doubling slack, per-segment fragmentation, and pointer-array overhead at 100K and 1M file scales, then propose five remediation paths ranked by effort/payoff: pre-size from getdents count, bumpalo arena, typed-arena, custom slab pool, and inline-string path collapse. Recommend stacking the cheapest two for an estimated 40-50 MiB win at 1M entries.
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Document the container-level RSS gap between oc-rsync's Vec<FileEntry> + segmented file lists and upstream rsync's pool_alloc.c slab arena. Quantify Vec doubling slack, per-segment fragmentation, and pointer-array overhead at 100K and 1M file scales, then propose five remediation paths ranked by effort/payoff: pre-size from getdents count, bumpalo arena, typed-arena, custom slab pool, and inline-string path collapse. Recommend stacking the cheapest two for an estimated 40-50 MiB win at 1M entries.
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Summary
Vec<FileEntry>(plus segmented per-directory vectors) and upstream rsync'spool_alloc.cslab arena.Vecdoubling slack, per-segment fragmentation, and pointer-array overhead at 100K and 1M file scales; cross-check against the empirical 42.6 vs 7.9 MiB Mode-B baseline.getdentscount,bumpaloarena,typed-arena, custom slab pool, and inline-stringname+dirnamecollapse. Recommend stacking pre-size + path collapse for ~40-50 MiB win at 1M entries with no API breakage.Task: #1050. Companion to #1048 (path-heap), #966 (overall RSS), #971 (1M-file scaling).
Test plan
crates/protocol/src/flist/*andtarget/interop/upstream-src/rsync-3.4.1/{flist.c,rsync.h,lib/pool_alloc.c}.