src/pkg/runtime/mprof.goc

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Malloc profiling.
// Patterned after tcmalloc's algorithms; shorter code.

package runtime
#include "runtime.h"
#include "malloc.h"
#include "defs.h"
#include "type.h"

// NOTE(rsc): Everything here could use cas if contention became an issue.
static Lock proflock;

// Per-call-stack allocation information.
// Lookup by hashing call stack into a linked-list hash table.
typedef struct Bucket Bucket;
struct Bucket
{
	Bucket	*next;	// next in hash list
	Bucket	*allnext;	// next in list of all buckets
	uintptr	allocs;
	uintptr	frees;
	uintptr	alloc_bytes;
	uintptr	free_bytes;
	uintptr	hash;
	uintptr	nstk;
	uintptr	stk[1];
};
enum {
	BuckHashSize = 179999,
};
static Bucket **buckhash;
static Bucket *buckets;
static uintptr bucketmem;

// Return the bucket for stk[0:nstk], allocating new bucket if needed.
static Bucket*
stkbucket(uintptr *stk, int32 nstk)
{
	int32 i;
	uintptr h;
	Bucket *b;

	if(buckhash == nil) {
		buckhash = SysAlloc(BuckHashSize*sizeof buckhash[0]);
		mstats.buckhash_sys += BuckHashSize*sizeof buckhash[0];
	}

	// Hash stack.
	h = 0;
	for(i=0; i<nstk; i++) {
		h += stk[i];
		h += h<<10;
		h ^= h>>6;
	}
	h += h<<3;
	h ^= h>>11;

	i = h%BuckHashSize;
	for(b = buckhash[i]; b; b=b->next)
		if(b->hash == h && b->nstk == nstk &&
		   mcmp((byte*)b->stk, (byte*)stk, nstk*sizeof stk[0]) == 0)
			return b;

	b = mallocgc(sizeof *b + nstk*sizeof stk[0], RefNoProfiling, 0, 1);
	bucketmem += sizeof *b + nstk*sizeof stk[0];
	memmove(b->stk, stk, nstk*sizeof stk[0]);
	b->hash = h;
	b->nstk = nstk;
	b->next = buckhash[i];
	buckhash[i] = b;
	b->allnext = buckets;
	buckets = b;
	return b;
}

// Map from pointer to Bucket* that allocated it.
// Three levels:
//	Linked-list hash table for top N-20 bits.
//	Array index for next 13 bits.
//	Linked list for next 7 bits.
// This is more efficient than using a general map,
// because of the typical clustering of the pointer keys.

typedef struct AddrHash AddrHash;
typedef struct AddrEntry AddrEntry;

struct AddrHash
{
	AddrHash *next;	// next in top-level hash table linked list
	uintptr addr;	// addr>>20
	AddrEntry *dense[1<<13];
};

struct AddrEntry
{
	AddrEntry *next;	// next in bottom-level linked list
	uint32 addr;
	Bucket *b;
};

enum {
	AddrHashBits = 12	// 1MB per entry, so good for 4GB of used address space
};
static AddrHash *addrhash[1<<AddrHashBits];
static AddrEntry *addrfree;
static uintptr addrmem;

// Multiplicative hash function:
// hashMultiplier is the bottom 32 bits of int((sqrt(5)-1)/2 * (1<<32)).
// This is a good multiplier as suggested in CLR, Knuth.  The hash
// value is taken to be the top AddrHashBits bits of the bottom 32 bits
// of the muliplied value.
enum {
	HashMultiplier = 2654435769U
};

// Set the bucket associated with addr to b.
static void
setaddrbucket(uintptr addr, Bucket *b)
{
	int32 i;
	uint32 h;
	AddrHash *ah;
	AddrEntry *e;

	h = (uint32)((addr>>20)*HashMultiplier) >> (32-AddrHashBits);
	for(ah=addrhash[h]; ah; ah=ah->next)
		if(ah->addr == (addr>>20))
			goto found;

	ah = mallocgc(sizeof *ah, RefNoProfiling, 0, 1);
	addrmem += sizeof *ah;
	ah->next = addrhash[h];
	ah->addr = addr>>20;
	addrhash[h] = ah;

found:
	if((e = addrfree) == nil) {
		e = mallocgc(64*sizeof *e, RefNoProfiling, 0, 0);
		addrmem += 64*sizeof *e;
		for(i=0; i+1<64; i++)
			e[i].next = &e[i+1];
		e[63].next = nil;
	}
	addrfree = e->next;
	e->addr = (uint32)~(addr & ((1<<20)-1));
	e->b = b;
	h = (addr>>7)&(nelem(ah->dense)-1);	// entry in dense is top 13 bits of low 20.
	e->next = ah->dense[h];
	ah->dense[h] = e;
}

// Get the bucket associated with addr and clear the association.
static Bucket*
getaddrbucket(uintptr addr)
{
	uint32 h;
	AddrHash *ah;
	AddrEntry *e, **l;
	Bucket *b;

	h = (uint32)((addr>>20)*HashMultiplier) >> (32-AddrHashBits);
	for(ah=addrhash[h]; ah; ah=ah->next)
		if(ah->addr == (addr>>20))
			goto found;
	return nil;

found:
	h = (addr>>7)&(nelem(ah->dense)-1);	// entry in dense is top 13 bits of low 20.
	for(l=&ah->dense[h]; (e=*l) != nil; l=&e->next) {
		if(e->addr == (uint32)~(addr & ((1<<20)-1))) {
			*l = e->next;
			b = e->b;
			e->next = addrfree;
			addrfree = e;
			return b;
		}
	}
	return nil;
}

// Called by malloc to record a profiled block.
void
MProf_Malloc(void *p, uintptr size)
{
	int32 nstk;
	uintptr stk[32];
	Bucket *b;

	if(m->nomemprof > 0)
		return;

	m->nomemprof++;
	nstk = callers(1, stk, 32);
	lock(&proflock);
	b = stkbucket(stk, nstk);
	b->allocs++;
	b->alloc_bytes += size;
	setaddrbucket((uintptr)p, b);
	unlock(&proflock);
	m->nomemprof--;
}

// Called when freeing a profiled block.
void
MProf_Free(void *p, uintptr size)
{
	Bucket *b;

	if(m->nomemprof > 0)
		return;

	m->nomemprof++;
	lock(&proflock);
	b = getaddrbucket((uintptr)p);
	if(b != nil) {
		b->frees++;
		b->free_bytes += size;
	}
	unlock(&proflock);
	m->nomemprof--;
}


// Go interface to profile data.  (Declared in extern.go)
// Assumes Go sizeof(int) == sizeof(int32)

// Must match MemProfileRecord in extern.go.
typedef struct Record Record;
struct Record {
	int64 alloc_bytes, free_bytes;
	int64 alloc_objects, free_objects;
	uintptr stk[32];
};

// Write b's data to r.
static void
record(Record *r, Bucket *b)
{
	int32 i;

	r->alloc_bytes = b->alloc_bytes;
	r->free_bytes = b->free_bytes;
	r->alloc_objects = b->allocs;
	r->free_objects = b->frees;
	for(i=0; i<b->nstk && i<nelem(r->stk); i++)
		r->stk[i] = b->stk[i];
	for(; i<nelem(r->stk); i++)
		r->stk[i] = 0;
}

func MemProfile(p Slice, include_inuse_zero bool) (n int32, ok bool) {
	Bucket *b;
	Record *r;

	lock(&proflock);
	n = 0;
	for(b=buckets; b; b=b->allnext)
		if(include_inuse_zero || b->alloc_bytes != b->free_bytes)
			n++;
	ok = false;
	if(n <= p.len) {
		ok = true;
		r = (Record*)p.array;
		for(b=buckets; b; b=b->allnext)
			if(include_inuse_zero || b->alloc_bytes != b->free_bytes)
				record(r++, b);
	}
	unlock(&proflock);
}