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Bug 312238: gcBytes and gcPrivateBytes from JSRuntime now means the total 

amount of memory allocated by GC arenas, not the size of allocated things
which does not include the memory taken by free GC cells. This simplified
accounting and allows to implement lock-less allocation of GC things.
This commit is contained in:
igor%mir2.org 2006-04-20 15:33:35 +00:00
Родитель e76f551ffd
Коммит f63b1ca6f0
2 изменённых файлов: 98 добавлений и 61 удалений
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51
js/src/jsapi.c
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@ -1866,13 +1866,54 @@ JS_MaybeGC(JSContext *cx)
rt = cx->runtime;
bytes = rt->gcBytes;
lastBytes = rt->gcLastBytes;
if ((bytes > 8192 && bytes > lastBytes + lastBytes / 2) ||
rt->gcMallocBytes > rt->gcMaxMallocBytes) {
/*
* Run the GC if we have half again as many bytes of GC-things as
* the last time we GC'd, or if we have malloc'd more bytes through
* JS_malloc than we were told to allocate by JS_NewRuntime.
* We run the GC if we used all available free GC cells and had to
* allocate extra 1/16 of GC arenas since the last run of GC, or if
* we have malloc'd more bytes through JS_malloc than we were told
* to allocate by JS_NewRuntime.
*
* The reason for
* bytes > 17/16 lastBytes
* condition is the following. Bug 312238 changed bytes and lastBytes
* to mean the total amount of memory that the GC uses now and right
* after the last GC.
*
* Before the bug the variables meant the size of allocated GC things
* now and right after the last GC. That size did not include the
* memory taken by free GC cells and the condition was
* bytes > 3/2 lastBytes.
* That is, we run the GC if we have half again as many bytes of
* GC-things as the last time we GC'd. To be compatible we need to
* express that condition through the new meaning of bytes and
* lastBytes.
*
* We write the original condition as
* B*(1-F) > 3/2 Bl*(1-Fl)
* where B is the total memory size allocated by GC and F is the free
* cell density currently and Sl and Fl are the size and the density
* right after GC. The density by definition is memory taken by free
* cells divided by total amount of memory. In other words, B and Bl
* are bytes and lastBytes with the new meaning and B*(1-F) and
* Bl*(1-Fl) are bytes and lastBytes with the original meaning.
*
* Our task is to exclude F and Fl from the last statement. According
* the stats from bug 331770 Fl is about 25-30% for GC allocations
* that contribute to S and Sl for a typical run of the browser. It
* means that the original condition implied that we did not run GC
* unless we exhausted the pool of free cells. Indeed if we still
* have free cells, then B == Bl since we did not yet allocated any
* new arenas and the condition means
* 1 - F > 3/2 (1-Fl) or 3/2Fl > 1/2 + F
* That implies 3/2 Fl > 1/2 or Fl > 1/3. That can not be fulfilled
* for the state described by the stats. So we can write the original
* condition as:
* F == 0 && B > 3/2 Bl(1-Fl)
* Again using the stats we approximate that by B > 17/16 Bl which
* corresponds to using 29% as an average value of Fl.
*/
if ((bytes > 8192 && bytes > lastBytes + lastBytes / 16) ||
rt->gcMallocBytes > rt->gcMaxMallocBytes) {
JS_GC(cx);
}
#endif

70
js/src/jsgc.c
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@ -188,6 +188,9 @@ struct JSGCArena {
uint8 base[1]; /* things+flags allocation area */
};
#define GC_ARENA_SIZE \
(offsetof(JSGCArena, base) + GC_THINGS_SIZE + GC_FLAGS_SIZE)
#define FIRST_THING_PAGE(a) \
(((jsuword)(a)->base + GC_FLAGS_SIZE - 1) & ~GC_PAGE_MASK)
@ -233,7 +236,7 @@ NewGCArena(JSGCArenaList *arenaList, size_t nbytes)
jsuword offset;
JSGCPageInfo *pi;
a = malloc(offsetof(JSGCArena, base) + GC_THINGS_SIZE + GC_FLAGS_SIZE);
a = malloc(GC_ARENA_SIZE);
if (!a)
return JS_FALSE;
@ -274,8 +277,7 @@ DestroyGCArena(JSGCArenaList *arenaList, JSGCArena **ap)
*ap = a->prev;
#ifdef DEBUG
memset(a, JS_FREE_PATTERN,
offsetof(JSGCArena, base) + GC_THINGS_SIZE + GC_FLAGS_SIZE);
memset(a, JS_FREE_PATTERN, GC_ARENA_SIZE);
#endif
free(a);
}
@ -671,10 +673,10 @@ unsigned gchpos;
void *
js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
{
JSBool tried_gc;
JSRuntime *rt;
size_t nflags;
uintN alindex;
JSGCArenaList *arenaList;
JSBool triedGC;
JSGCThing *thing;
uint8 *flagp;
jsuword offset;
@ -682,6 +684,10 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
uint32 *bytesptr;
rt = cx->runtime;
nbytes = JS_ROUNDUP(nbytes, sizeof(JSGCThing));
alindex = GC_FREELIST_INDEX(nbytes);
arenaList = &rt->gcArenaList[alindex];
JS_LOCK_GC(rt);
JS_ASSERT(!rt->gcRunning);
if (rt->gcRunning) {
@ -695,15 +701,12 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
rt->gcPoke = JS_TRUE;
#endif
js_GC(cx, GC_KEEP_ATOMS | GC_ALREADY_LOCKED);
tried_gc = JS_TRUE;
triedGC = JS_TRUE;
#else
tried_gc = JS_FALSE;
triedGC = JS_FALSE;
#endif
METER(rt->gcStats.alloc++);
nbytes = JS_ROUNDUP(nbytes, sizeof(JSGCThing));
nflags = nbytes / sizeof(JSGCThing);
arenaList = &rt->gcArenaList[GC_FREELIST_INDEX(nbytes)];
/* Loop to repeat allocation after forced GC. */
for (;;) {
@ -717,27 +720,31 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
break;
}
/*
* The free list is empty, check if we can allocate more memory from
* arenaList.
*/
if (rt->gcBytes < rt->gcMaxBytes &&
(tried_gc || rt->gcMallocBytes < rt->gcMaxMallocBytes)) {
if (!arenaList->last || arenaList->lastLimit == GC_THINGS_SIZE) {
/*
* The last arena (and the whole arenaList) is full, time
* to allocate new one.
* The free list is empty and the last arena is full.
* Check if we allowed to allocate a new arena.
*/
if (rt->gcBytes >= rt->gcMaxBytes)
goto try_gc;
if (!triedGC && rt->gcMallocBytes >= rt->gcMaxMallocBytes)
goto try_gc;
if (!NewGCArena(arenaList, nbytes))
goto try_gc;
bytesptr = (alindex != 0) ? &rt->gcPrivateBytes : &rt->gcBytes;
*bytesptr += GC_ARENA_SIZE;
}
offset = arenaList->lastLimit;
if ((offset & GC_PAGE_MASK) == 0) {
/* Skip JSGCPageInfo record located at GC_PAGE_SIZE boundary. */
offset += PAGE_THING_GAP(nbytes);
}
/* Assert that at this point space for things should exist. */
/*
* At this point, the last arena should have space for more things.
*/
JS_ASSERT(offset + nbytes <= GC_THINGS_SIZE);
arenaList->lastLimit = (uint16)(offset + nbytes);
thing = (JSGCThing *)(FIRST_THING_PAGE(arenaList->last) + offset);
@ -746,7 +753,6 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
METER(arenaList->stats.maxthings =
JS_MAX(arenaList->stats.nthings, arenaList->stats.maxthings));
break;
}
/*
* Consider doing a "last ditch" GC if thing couldn't be allocated.
@ -759,7 +765,7 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
* (http://bugzilla.mozilla.org/show_bug.cgi?id=162779).
*/
try_gc:
if (tried_gc)
if (triedGC)
goto fail;
rt->gcPoke = JS_TRUE;
js_GC(cx, GC_KEEP_ATOMS | GC_ALREADY_LOCKED);
@ -769,7 +775,7 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
JS_UNLOCK_GC(rt);
return NULL;
}
tried_gc = JS_TRUE;
triedGC = JS_TRUE;
METER(rt->gcStats.retry++);
}
@ -794,10 +800,6 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
/* We can't fail now, so update flags and rt->gc{,Private}Bytes. */
*flagp = (uint8)flags;
bytesptr = ((flags & GCF_TYPEMASK) == GCX_PRIVATE)
? &rt->gcPrivateBytes
: &rt->gcBytes;
*bytesptr += nbytes + nflags;
/*
* Clear thing before unlocking in case a GC run is about to scan it,
@ -806,7 +808,7 @@ js_NewGCThing(JSContext *cx, uintN flags, size_t nbytes)
thing->next = NULL;
thing->flagp = NULL;
#ifdef DEBUG_gchist
gchist[gchpos].lastDitch = tried_gc;
gchist[gchpos].lastDitch = triedGC;
gchist[gchpos].freeList = arenaList->freeList;
if (++gchpos == NGCHIST)
gchpos = 0;
@ -1821,7 +1823,7 @@ js_GC(JSContext *cx, uintN gcflags)
uintN i, type;
JSStackHeader *sh;
JSTempValueRooter *tvr;
size_t nbytes, nflags, limit, offset;
size_t nbytes, limit, offset;
JSGCArena *a, **ap;
uint8 flags, *flagp, *firstPage;
JSGCThing *thing, *freeList;
@ -2106,8 +2108,6 @@ restart:
for (i = 0; i < GC_NUM_FREELISTS; i++) {
arenaList = &rt->gcArenaList[i];
nbytes = GC_FREELIST_NBYTES(i);
nflags = nbytes / sizeof(JSGCThing);
limit = arenaList->lastLimit;
for (a = arenaList->last; a; a = a->prev) {
JS_ASSERT(!a->prevUnscanned);
@ -2140,13 +2140,6 @@ restart:
/* Set flags to GCF_FINAL, signifying that thing is free. */
*flagp = GCF_FINAL;
bytesptr = (type == GCX_PRIVATE)
? &rt->gcPrivateBytes
: &rt->gcBytes;
JS_ASSERT(*bytesptr >= nbytes + nflags);
*bytesptr -= nbytes + nflags;
}
}
limit = GC_THINGS_SIZE;
@ -2209,6 +2202,9 @@ restart:
*/
freeList = arenaList->freeList;
DestroyGCArena(arenaList, ap);
bytesptr = (i != 0) ? &rt->gcPrivateBytes : &rt->gcBytes;
JS_ASSERT(*bytesptr >= GC_ARENA_SIZE);
*bytesptr -= GC_ARENA_SIZE;
METER(rt->gcStats.afree++);
} else {
all_clear = JS_TRUE;