Dear Gophers: I have some questions about GC and map[int]int, please help.
consider the following program: ```go package main import ( "fmt" "os" "runtime/pprof" ) func main() { f, err := os.OpenFile("memory.pb.gz", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666 ) if err != nil { panic(err) } m := make(map[int]int) for i := 0; i < 10e6; i++ { m[i] = 2 * i } if err := pprof.WriteHeapProfile(f); err != nil { panic(err) } } ``` after inserting 10 million key/value pair, the result of this memory profile show inuse_objects count ~ 100k [image: inuse_objects.png] in my view this inuse_objects is found by GC by following the bucket and old_buckets pointer of hmap ```go // A header for a Go map. type hmap struct { // Note: the format of the hmap is also encoded in cmd/compile/internal/reflectdata/reflect.go. // Make sure this stays in sync with the compiler's definition. count int // # live cells == size of map. Must be first (used by len() builtin) flags uint8 B uint8 // log_2 of # of buckets (can hold up to loadFactor * 2^B items) noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details hash0 uint32 // hash seed buckets unsafe.Pointer // array of 2^B Buckets. may be nil if count==0. oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing nevacuate uintptr // progress counter for evacuation (buckets less than this have been evacuated) extra *mapextra // optional fields } ``` but according to this doc: https://go101.org/optimizations/6-map.html If the key type and element type of a map both don't contain pointers, then in the scan phase of a GC cycle, the garbage collector will not scan the entries of the map. This could save much time. My question is: maybe GC should not follow the bucket and old_buckets pointer of hmap? or the doc above just forbid GC from scan the entries not the bucket and old_buckets pointer of hmap, and larger map[int]int do increase GC scan overhead by having more buckets and old_buckets? Thanks -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/db9507eb-fd64-46c0-867a-f4eaf5c78b38n%40googlegroups.com.