Resize-in-place for large allocs. (Shrink-only) #289

dsm9000 · 2023-09-04T03:23:46Z

In re: #265 .
realloc() now resizes in place when possible, using appropriate size class.
Currently only supports realloc() downwards.

sdlib/d/gc/tcache.d

sdlib/d/gc/arena.d

sdlib/d/gc/emap.d

sdlib/d/gc/hpd.d

sdlib/d/gc/arena.d

deadalnix · 2023-09-07T20:52:54Z

sdlib/d/gc/arena.d

+		uint oldSize = cast(uint) e.size;
+		uint oldPages = oldSize / PageSize;


The cast should be on oldPages. Also, it's the currentSize.

deadalnix · 2023-09-07T21:25:24Z

sdlib/d/gc/arena.d

+
+		auto computedPageCount = alignUp(size, PageSize) / PageSize;
+		uint newPages = computedPageCount & uint.max;
+


Remove that empty line. the assert being on its own is quite confusing as it's not obvious that it is just a sanity check on the previous computation (check that there is no truncation going on, which should be impossible considering the allocatable size we have).

sdlib/d/gc/arena.d

deadalnix · 2023-09-07T21:29:43Z

sdlib/d/gc/arena.d

+		e.at(e.address, newPages * PageSize, hpd);
+		hpd.clear(n + newPages, oldPages - newPages);


This tells me what you actually need as input is e, n + newPages, newPages, delta. It's 4 just as before, but it maps to what you actually need in there.

Probably named e, index, pages, delta.

deadalnix · 2023-09-07T21:34:10Z

This is looking good, but there is probably some simplification in argument passing in the various functions in the arena.

maxhaton · 2023-09-07T22:11:20Z

sdlib/d/gc/arena.d

+		assert(isLargeSize(size));
+
+		// Huge is not supported:
+		if (e.isHuge()) {


Can this happen if the isLarge assert pass.

Yes, please see definition, isLarge includes any extent that isn't a slab.

deadalnix · 2023-09-08T12:33:40Z

sdlib/d/gc/arena.d

@@ -338,6 +392,22 @@ private:
 		unusedExtents.insert(e);
 	}

+	void shrinkAllocImpl(Extent* e, uint index, uint pages, uint delta) {
+		assert(mutex.isHeld(), "Mutex not held!");
+		assert(index <= PageCount - pages, "Invalid index!");


Not a blocker, but index > 0.

Thank you, fixed.

deadalnix · 2023-09-08T14:43:54Z

sdlib/d/gc/arena.d

+		auto currentSize = e.size;
+		uint oldPages = cast(uint) (currentSize / PageSize);


e.pageCount

deadalnix · 2023-09-08T14:44:48Z

sdlib/d/gc/arena.d

+		uint currentPages = cast(uint) (e.size / PageSize);
+		assert(currentPages > pages, "Invalid shrink pages!");


e.pageCount

deadalnix · 2023-09-08T14:49:46Z

sdlib/d/gc/arena.d

+		auto hpd = e.hpd;
+		unregisterHPD(hpd);
+
+		e.at(e.address, pages * PageSize, hpd);
+		hpd.clear(index, delta);
+
+		assert(!hpd.empty);
+		registerHPD(hpd);


This is great how clean this became.

deadalnix · 2023-09-08T15:34:12Z

sdlib/d/gc/arena.d

+
+		uint delta = currentPages - pages;
+
+		uint n = ((cast(size_t) e.address) / PageSize) % PageCount;


deadalnix · 2023-09-08T16:10:43Z

sdlib/d/gc/arena.d

+		auto computedPageCount = alignUp(size, PageSize) / PageSize;
+		uint newPages = computedPageCount & uint.max;
+		assert(newPages == computedPageCount, "Unexpected page count!");


getPageCount

deadalnix · 2023-09-08T16:12:03Z

sdlib/d/gc/tcache.d

 	auto p4 = threadCache.realloc(p3, 16000, false);
-	assert(p4 !is p3);
+	assert(p4 is p3);
 	assert(threadCache.getCapacity(p4[0 .. 16000]) == 16384);


Is there a test shrink from large to small?

dsm9000 added 3 commits September 3, 2023 23:21

first try at resize-in-place for large allocs.

49640db

first try at resize-in-place for large allocs. (minor corrections)

355d5d0

first try at resize-in-place for large allocs. (minor corrections)

f5febbd