Issue #15631 has been updated by methodmissing (Lourens Naud=E9). Thanks for raising this Pavel. `st_init_table_with_size(0)` effectively also allocates additional capacity= , but if and how quickly the hash tables mutate I'll investigate later. References https://github.com/ruby/ruby/blob/trunk/st.c#L573-L578 , https:/= /github.com/ruby/ruby/blob/trunk/st.c#L595 and https://github.com/ruby/ruby= /blob/trunk/st.c#L332-L359 A simple peek suggests a total table size of 152 bytes on init, but will in= vestigate time to mutation of these 0 sized tables this evening: ``` diff --git a/st.c b/st.c index ed235c674e..f2b99d7771 100644 --- a/st.c +++ b/st.c @@ -615,6 +615,8 @@ st_init_table_with_size(const struct st_hash_type *type= , st_index_t size) #ifdef ST_DEBUG st_check(tab); #endif + printf("# st_init_table_with_size(%d) -> %d (%d)\n", size, n, st_memsi= ze(tab)); + return tab; } ``` ``` linking miniruby # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(102) -> 7 (3384) # st_init_table_with_size(255) -> 8 (7224) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(1000) -> 10 (28728) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(1000) -> 10 (28728) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(7) -> 3 (248) # st_init_table_with_size(15) -> 4 (440) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(16) -> 5 (888) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) # st_init_table_with_size(0) -> 2 (152) ``` ahorek (Pavel Rosick=FD) wrote: > right now round_capa value is rounded up to the next power of 2 > ``` > round_capa(4) -> returns 8 > round_capa(8) -> returns 16 > round_capa(16) -> returns 32 > = > round_capa(5) -> returns 8 > round_capa(9) -> returns 16 > round_capa(17) -> returns 32 > etc. > ``` > = > it seems wasteful to allocate the extra items capacity, so this PR change= s that to > ``` > round_capa(4) -> returns 4 > round_capa(8) -> returns 8 > round_capa(16) -> returns 16 > = > round_capa(5) -> returns 8 > round_capa(9) -> returns 16 > round_capa(17) -> returns 32 > etc. > ``` > = > the main purpose is to reduce memory usage especially during boot > = > my patch also uses BUILTIN_CLZ macro instead of shifts that makes it slig= htly faster > = > here's a benchmark > ```ruby > require 'benchmark/ips' > = > Benchmark.ips do |x| > x.config(time: 20, warmup: 3) > = > x.report('struct', "Struct.new(*('a'..'z').map { |x| x.to_sym })") > end > ``` > = > ``` > trunk > Warming up -------------------------------------- > struct 527.000 i/100ms > Calculating ------------------------------------- > struct 5.461k (=B1 5.5%) i/s - 109.089k in 20.0402= 53s > = > methodmising - POW2_P (github) > Warming up -------------------------------------- > struct 544.000 i/100ms > Calculating ------------------------------------- > struct 5.570k (=B1 4.1%) i/s - 111.520k in 20.0572= 45s > = > ahorek - BUILTIN_CLZ (id_table.c.patch) > Warming up -------------------------------------- > struct 571.000 i/100ms > Calculating ------------------------------------- > struct 5.812k (=B1 3.6%) i/s - 116.484k in 20.0706= 07s > ``` > = > discussion https://github.com/ruby/ruby/pull/2083 ---------------------------------------- Feature #15631: Let round_capa for ID table not allocate excess capacity fo= r power of 2 ints >=3D 4 https://bugs.ruby-lang.org/issues/15631#change-77049 * Author: ahorek (Pavel Rosick=FD) * Status: Open * Priority: Normal * Assignee: = * Target version: = ---------------------------------------- right now round_capa value is rounded up to the next power of 2 ``` round_capa(4) -> returns 8 round_capa(8) -> returns 16 round_capa(16) -> returns 32 round_capa(5) -> returns 8 round_capa(9) -> returns 16 round_capa(17) -> returns 32 etc. ``` it seems wasteful to allocate the extra items capacity, so this PR changes = that to ``` round_capa(4) -> returns 4 round_capa(8) -> returns 8 round_capa(16) -> returns 16 round_capa(5) -> returns 8 round_capa(9) -> returns 16 round_capa(17) -> returns 32 etc. ``` the main purpose is to reduce memory usage especially during boot my patch also uses BUILTIN_CLZ macro instead of shifts that makes it slight= ly faster here's a benchmark ```ruby require 'benchmark/ips' Benchmark.ips do |x| x.config(time: 20, warmup: 3) x.report('struct', "Struct.new(*('a'..'z').map { |x| x.to_sym })") end ``` ``` trunk Warming up -------------------------------------- struct 527.000 i/100ms Calculating ------------------------------------- struct 5.461k (=B1 5.5%) i/s - 109.089k in 20.040253s methodmising - POW2_P (github) Warming up -------------------------------------- struct 544.000 i/100ms Calculating ------------------------------------- struct 5.570k (=B1 4.1%) i/s - 111.520k in 20.057245s ahorek - BUILTIN_CLZ (id_table.c.patch) Warming up -------------------------------------- struct 571.000 i/100ms Calculating ------------------------------------- struct 5.812k (=B1 3.6%) i/s - 116.484k in 20.070607s ``` discussion https://github.com/ruby/ruby/pull/2083 ---Files-------------------------------- id_table.c.patch (534 Bytes) -- = https://bugs.ruby-lang.org/ Unsubscribe: <mailto:ruby-core-request / ruby-lang.org?subject=3Dunsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>