Eric Wong <e@xxxxxxxxx> writes:
> Fortunately, this set of changes is unintrusive; but I'm
> hoping to have more time to make deeper changes this year.
>
> Eric Wong (3):
> list-objects-filter: use kh_size API
> treewide: switch to khashl for memory savings
> khashl: fix ensemble lookups on empty table
>
> builtin/fast-import.c | 2 +-
> builtin/fsmonitor--daemon.c | 4 +-
> delta-islands.c | 4 +-
> khash.h | 338 -----------------------
> khashl.h | 522 ++++++++++++++++++++++++++++++++++++
> list-objects-filter.c | 2 +-
> object-store-ll.h | 2 +-
> object-store.h | 7 +-
> oidset.h | 2 +-
> pack-bitmap.h | 2 +-
> 10 files changed, 535 insertions(+), 350 deletions(-)
> delete mode 100644 khash.h
> create mode 100644 khashl.h
>
> Range-diff:
> -: ---------- > 1: 3bf3148cab list-objects-filter: use kh_size API
> 1: e74965907e ! 2: 09900edb48 treewide: switch to khashl for memory savings
Do you have the correct range-diff? The previous round had the
change to the list-object-filter.c to use kh_size() already.
But I see the 0 -> NULL fixes. Perhaps the left-side base was off
by one when you took the range-diff and there is nothing else going
on that we should be worried about...
> @@ Commit message
>
> khashl is an updated version of khash with less memory overhead
> (one bit/bucket instead of two) than the original khash and
> - similar overall performance. Insertions are simpler (linear
> - probing) but deletions may be slightly slower[1]. Of course,
> - the majority of hash tables in git do not delete individual
> - elements.
> + similar overall performance. According to its author,
> + insertions are simpler (linear probing) but deletions may be
> + slightly slower[1]. Of course, the majority of hash tables in
> + git do not delete individual elements.
>
> Overall memory usage did not decrease much, as the hash tables
> and elements we store in them are big and currently dwarf the
> overhead of the khash internals. Only around 10 MB in
> - allocations (not peak use) is saved when doing a no-op `git gc'
> - of a Linux kernel object store with thousands of refs and
> - islands.
> + allocations (and a few dozen KB peak use out of ~6 GB) is saved
> + when doing a no-op `git gc' of a Linux kernel object store with
> + thousands of refs and islands.
>
> A summary of differences I've found from khash to khashl:
>
> @@ Commit message
> * flesh out KHASHL_{SET,MAP}_INIT wrappers with *_clear, *_resize,
> and *_release functions
>
> + * sparse fixes from Junio and Jeff
> +
> [1] https://attractivechaos.wordpress.com/2019/12/28/deletion-from-hash-tables-without-tombstones/
> [2] git clone https://github.com/attractivechaos/klib.git
> 2895a16cb55e (support an ensemble of hash tables, 2023-12-18)
> @@ Commit message
> typedef) and was the only place where I had to change a definition.
>
> Signed-off-by: Eric Wong <e@xxxxxxxxx>
> + Helped-by: Junio C Hamano <gitster@xxxxxxxxx>
> + Helped-by: Jeff King <peff@xxxxxxxx>
>
> ## builtin/fast-import.c ##
> @@
> @@ khashl.h (new)
> +#define __KHASHL_IMPL_GET(SCOPE, HType, prefix, khkey_t, __hash_fn, __hash_eq) \
> + SCOPE khint_t prefix##_getp_core(const HType *h, const khkey_t *key, khint_t hash) { \
> + khint_t i, last, n_buckets, mask; \
> -+ if (h->keys == 0) return 0; \
> ++ if (!h->keys) return 0; \
> + n_buckets = (khint_t)1U << h->bits; \
> + mask = n_buckets - 1U; \
> + i = last = __kh_h2b(hash, h->bits); \
> @@ khashl.h (new)
> +
> +#define __KHASHL_IMPL_RESIZE(SCOPE, HType, prefix, khkey_t, __hash_fn, __hash_eq) \
> + SCOPE void prefix##_resize(HType *h, khint_t new_n_buckets) { \
> -+ khint32_t *new_used = 0; \
> ++ khint32_t *new_used = NULL; \
> + khint_t j = 0, x = new_n_buckets, n_buckets, new_bits, new_mask; \
> + while ((x >>= 1) != 0) ++j; \
> + if (new_n_buckets & (new_n_buckets - 1)) ++j; \
> @@ khashl.h (new)
> +#define __KHASHL_IMPL_DEL(SCOPE, HType, prefix, khkey_t, __hash_fn) \
> + SCOPE int prefix##_del(HType *h, khint_t i) { \
> + khint_t j = i, k, mask, n_buckets; \
> -+ if (h->keys == 0) return 0; \
> ++ if (!h->keys) return 0; \
> + n_buckets = (khint_t)1U<<h->bits; \
> + mask = n_buckets - 1U; \
> + while (1) { \
> 2: 744e1b7198 = 3: bfb20eae37 khashl: fix ensemble lookups on empty table
