2012-01-13 Paul Thomas <pault@gcc.gnu.org>

[official-gcc.git] / libgo / runtime / mheap.c

// 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.

// Page heap.
//
// See malloc.h for overview.
//
// When a MSpan is in the heap free list, state == MSpanFree
// and heapmap(s->start) == span, heapmap(s->start+s->npages-1) == span.
//
// When a MSpan is allocated, state == MSpanInUse
// and heapmap(i) == span for all s->start <= i < s->start+s->npages.

#include "runtime.h"
#include "arch.h"
#include "malloc.h"

static MSpan *MHeap_AllocLocked(MHeap*, uintptr, int32);
static bool MHeap_Grow(MHeap*, uintptr);
static void MHeap_FreeLocked(MHeap*, MSpan*);
static MSpan *MHeap_AllocLarge(MHeap*, uintptr);
static MSpan *BestFit(MSpan*, uintptr, MSpan*);

static void
RecordSpan(void *vh, byte *p)
{
        MHeap *h;
        MSpan *s;

        h = vh;
        s = (MSpan*)p;
        s->allnext = h->allspans;
        h->allspans = s;
}

// Initialize the heap; fetch memory using alloc.
void
runtime_MHeap_Init(MHeap *h, void *(*alloc)(uintptr))
{
        uint32 i;

        runtime_FixAlloc_Init(&h->spanalloc, sizeof(MSpan), alloc, RecordSpan, h);
        runtime_FixAlloc_Init(&h->cachealloc, sizeof(MCache), alloc, nil, nil);
        // h->mapcache needs no init
        for(i=0; i<nelem(h->free); i++)
                runtime_MSpanList_Init(&h->free[i]);
        runtime_MSpanList_Init(&h->large);
        for(i=0; i<nelem(h->central); i++)
                runtime_MCentral_Init(&h->central[i], i);
}

// Allocate a new span of npage pages from the heap
// and record its size class in the HeapMap and HeapMapCache.
MSpan*
runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, int32 acct)
{
        MSpan *s;

        runtime_lock(h);
        runtime_purgecachedstats(runtime_m());
        s = MHeap_AllocLocked(h, npage, sizeclass);
        if(s != nil) {
                mstats.heap_inuse += npage<<PageShift;
                if(acct) {
                        mstats.heap_objects++;
                        mstats.heap_alloc += npage<<PageShift;
                }
        }
        runtime_unlock(h);
        return s;
}

static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
        uintptr n;
        MSpan *s, *t;
        PageID p;

        // Try in fixed-size lists up to max.
        for(n=npage; n < nelem(h->free); n++) {
                if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
                        s = h->free[n].next;
                        goto HaveSpan;
                }
        }

        // Best fit in list of large spans.
        if((s = MHeap_AllocLarge(h, npage)) == nil) {
                if(!MHeap_Grow(h, npage))
                        return nil;
                if((s = MHeap_AllocLarge(h, npage)) == nil)
                        return nil;
        }

HaveSpan:
        // Mark span in use.
        if(s->state != MSpanFree)
                runtime_throw("MHeap_AllocLocked - MSpan not free");
        if(s->npages < npage)
                runtime_throw("MHeap_AllocLocked - bad npages");
        runtime_MSpanList_Remove(s);
        s->state = MSpanInUse;
        mstats.heap_idle -= s->npages<<PageShift;

        if(s->npages > npage) {
                // Trim extra and put it back in the heap.
                t = runtime_FixAlloc_Alloc(&h->spanalloc);
                mstats.mspan_inuse = h->spanalloc.inuse;
                mstats.mspan_sys = h->spanalloc.sys;
                runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
                s->npages = npage;
                p = t->start;
                if(sizeof(void*) == 8)
                        p -= ((uintptr)h->arena_start>>PageShift);
                if(p > 0)
                        h->map[p-1] = s;
                h->map[p] = t;
                h->map[p+t->npages-1] = t;
                *(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift);  // copy "needs zeroing" mark
                t->state = MSpanInUse;
                MHeap_FreeLocked(h, t);
        }

        if(*(uintptr*)(s->start<<PageShift) != 0)
                runtime_memclr((byte*)(s->start<<PageShift), s->npages<<PageShift);

        // Record span info, because gc needs to be
        // able to map interior pointer to containing span.
        s->sizeclass = sizeclass;
        p = s->start;
        if(sizeof(void*) == 8)
                p -= ((uintptr)h->arena_start>>PageShift);
        for(n=0; n<npage; n++)
                h->map[p+n] = s;
        return s;
}

// Allocate a span of exactly npage pages from the list of large spans.
static MSpan*
MHeap_AllocLarge(MHeap *h, uintptr npage)
{
        return BestFit(&h->large, npage, nil);
}

// Search list for smallest span with >= npage pages.
// If there are multiple smallest spans, take the one
// with the earliest starting address.
static MSpan*
BestFit(MSpan *list, uintptr npage, MSpan *best)
{
        MSpan *s;

        for(s=list->next; s != list; s=s->next) {
                if(s->npages < npage)
                        continue;
                if(best == nil
                || s->npages < best->npages
                || (s->npages == best->npages && s->start < best->start))
                        best = s;
        }
        return best;
}

// Try to add at least npage pages of memory to the heap,
// returning whether it worked.
static bool
MHeap_Grow(MHeap *h, uintptr npage)
{
        uintptr ask;
        void *v;
        MSpan *s;
        PageID p;

        // Ask for a big chunk, to reduce the number of mappings
        // the operating system needs to track; also amortizes
        // the overhead of an operating system mapping.
        // Allocate a multiple of 64kB (16 pages).
        npage = (npage+15)&~15;
        ask = npage<<PageShift;
        if(ask < HeapAllocChunk)
                ask = HeapAllocChunk;

        v = runtime_MHeap_SysAlloc(h, ask);
        if(v == nil) {
                if(ask > (npage<<PageShift)) {
                        ask = npage<<PageShift;
                        v = runtime_MHeap_SysAlloc(h, ask);
                }
                if(v == nil) {
                        runtime_printf("runtime: out of memory: cannot allocate %llu-byte block (%llu in use)\n", (unsigned long long)ask, (unsigned long long)mstats.heap_sys);
                        return false;
                }
        }
        mstats.heap_sys += ask;

        // Create a fake "in use" span and free it, so that the
        // right coalescing happens.
        s = runtime_FixAlloc_Alloc(&h->spanalloc);
        mstats.mspan_inuse = h->spanalloc.inuse;
        mstats.mspan_sys = h->spanalloc.sys;
        runtime_MSpan_Init(s, (uintptr)v>>PageShift, ask>>PageShift);
        p = s->start;
        if(sizeof(void*) == 8)
                p -= ((uintptr)h->arena_start>>PageShift);
        h->map[p] = s;
        h->map[p + s->npages - 1] = s;
        s->state = MSpanInUse;
        MHeap_FreeLocked(h, s);
        return true;
}

// Look up the span at the given address.
// Address is guaranteed to be in map
// and is guaranteed to be start or end of span.
MSpan*
runtime_MHeap_Lookup(MHeap *h, void *v)
{
        uintptr p;
        
        p = (uintptr)v;
        if(sizeof(void*) == 8)
                p -= (uintptr)h->arena_start;
        return h->map[p >> PageShift];
}

// Look up the span at the given address.
// Address is *not* guaranteed to be in map
// and may be anywhere in the span.
// Map entries for the middle of a span are only
// valid for allocated spans.  Free spans may have
// other garbage in their middles, so we have to
// check for that.
MSpan*
runtime_MHeap_LookupMaybe(MHeap *h, void *v)
{
        MSpan *s;
        PageID p, q;

        if((byte*)v < h->arena_start || (byte*)v >= h->arena_used)
                return nil;
        p = (uintptr)v>>PageShift;
        q = p;
        if(sizeof(void*) == 8)
                q -= (uintptr)h->arena_start >> PageShift;
        s = h->map[q];
        if(s == nil || p < s->start || p - s->start >= s->npages)
                return nil;
        if(s->state != MSpanInUse)
                return nil;
        return s;
}

// Free the span back into the heap.
void
runtime_MHeap_Free(MHeap *h, MSpan *s, int32 acct)
{
        runtime_lock(h);
        runtime_purgecachedstats(runtime_m());
        mstats.heap_inuse -= s->npages<<PageShift;
        if(acct) {
                mstats.heap_alloc -= s->npages<<PageShift;
                mstats.heap_objects--;
        }
        MHeap_FreeLocked(h, s);
        runtime_unlock(h);
}

static void
MHeap_FreeLocked(MHeap *h, MSpan *s)
{
        uintptr *sp, *tp;
        MSpan *t;
        PageID p;

        if(s->state != MSpanInUse || s->ref != 0) {
                // runtime_printf("MHeap_FreeLocked - span %p ptr %p state %d ref %d\n", s, s->start<<PageShift, s->state, s->ref);
                runtime_throw("MHeap_FreeLocked - invalid free");
        }
        mstats.heap_idle += s->npages<<PageShift;
        s->state = MSpanFree;
        runtime_MSpanList_Remove(s);
        sp = (uintptr*)(s->start<<PageShift);

        // Coalesce with earlier, later spans.
        p = s->start;
        if(sizeof(void*) == 8)
                p -= (uintptr)h->arena_start >> PageShift;
        if(p > 0 && (t = h->map[p-1]) != nil && t->state != MSpanInUse) {
                tp = (uintptr*)(t->start<<PageShift);
                *tp |= *sp;     // propagate "needs zeroing" mark
                s->start = t->start;
                s->npages += t->npages;
                p -= t->npages;
                h->map[p] = s;
                runtime_MSpanList_Remove(t);
                t->state = MSpanDead;
                runtime_FixAlloc_Free(&h->spanalloc, t);
                mstats.mspan_inuse = h->spanalloc.inuse;
                mstats.mspan_sys = h->spanalloc.sys;
        }
        if(p+s->npages < nelem(h->map) && (t = h->map[p+s->npages]) != nil && t->state != MSpanInUse) {
                tp = (uintptr*)(t->start<<PageShift);
                *sp |= *tp;     // propagate "needs zeroing" mark
                s->npages += t->npages;
                h->map[p + s->npages - 1] = s;
                runtime_MSpanList_Remove(t);
                t->state = MSpanDead;
                runtime_FixAlloc_Free(&h->spanalloc, t);
                mstats.mspan_inuse = h->spanalloc.inuse;
                mstats.mspan_sys = h->spanalloc.sys;
        }

        // Insert s into appropriate list.
        if(s->npages < nelem(h->free))
                runtime_MSpanList_Insert(&h->free[s->npages], s);
        else
                runtime_MSpanList_Insert(&h->large, s);

        // TODO(rsc): IncrementalScavenge() to return memory to OS.
}

// Initialize a new span with the given start and npages.
void
runtime_MSpan_Init(MSpan *span, PageID start, uintptr npages)
{
        span->next = nil;
        span->prev = nil;
        span->start = start;
        span->npages = npages;
        span->freelist = nil;
        span->ref = 0;
        span->sizeclass = 0;
        span->state = 0;
}

// Initialize an empty doubly-linked list.
void
runtime_MSpanList_Init(MSpan *list)
{
        list->state = MSpanListHead;
        list->next = list;
        list->prev = list;
}

void
runtime_MSpanList_Remove(MSpan *span)
{
        if(span->prev == nil && span->next == nil)
                return;
        span->prev->next = span->next;
        span->next->prev = span->prev;
        span->prev = nil;
        span->next = nil;
}

bool
runtime_MSpanList_IsEmpty(MSpan *list)
{
        return list->next == list;
}

void
runtime_MSpanList_Insert(MSpan *list, MSpan *span)
{
        if(span->next != nil || span->prev != nil) {
                // runtime_printf("failed MSpanList_Insert %p %p %p\n", span, span->next, span->prev);
                runtime_throw("MSpanList_Insert");
        }
        span->next = list->next;
        span->prev = list;
        span->next->prev = span;
        span->prev->next = span;
}