From 33dfb61f528905321bd863e16e44b1b29a30edac Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Wed, 3 Mar 2021 10:19:26 +0000
Subject: [PATCH] rts: Make allocatePinned always take a new block
This change surprisingly fixes quite bad fragmentation issues
When a new block was stolen from the nursery it meant that on the next
GC that the nursery had to be resized and the stolen block replaced.
This led to a few (1 or 2) random blocks from the free list being added to
the nursery, from which they would never escape. Over time, the rest of
the blocks in these megablocks would get collected but the nursery would hold onto 1
block from many different megablocks. This led to the situation where
there were many nearly empty megablocks in the free list.
---
rts/sm/Storage.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/rts/sm/Storage.c b/rts/sm/Storage.c
index 0a87e8fe5b6..38df8ffc4c8 100644
--- a/rts/sm/Storage.c
+++ b/rts/sm/Storage.c
@@ -1125,7 +1125,7 @@ allocatePinned (Capability *cap, W_ n)
// So first, we try taking the next block from the nursery, in
// the same way as allocate().
bd = cap->r.rCurrentNursery->link;
- if (bd == NULL) {
+ if (bd == NULL || true) {
// The nursery is empty: allocate a fresh block (we can't fail
// here).
ACQUIRE_SM_LOCK;
--
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