231917 2021-10-18 16:02:12 -0700 [bmalloc] Heap.shrinkLarge() allocates non-aligned region 2021-10-25 16:03:18 -0700 1 1 1 Unclassified WebKit bmalloc WebKit Nightly Build Unspecified Unspecified NEW InRadar P2 Normal --- 1 basuke webkit-unassigned fpizlo ggaren webkit-bug-importer oldest_to_newest 1805756 0 basuke 2021-10-18 16:02:12 -0700 Because the newly allocated region is not aligned well, unaligned region will be returned to LargeFree while splitAndAllocate() is called. Those regions won't match to any request to LargeFree until the neighbor region is returned to LargeFree and get merged with that. 1. Align 40k memory region A. Both start and end is aligned in 4k boundary. 2. realloc A to 36k + 1. shrinkLarge tries to split it in that size, B (36k +1) and C (4k - 1) 3. B's end is not aligned, but there's no practical issue. 4. On the other hand, C's start address is not aligned and sit in the LargeFree. It won't fit to any request because it's not aligned. 1805790 1 basuke 2021-10-18 17:09:42 -0700 Above description was wrong. Rewrote. Because the newly allocated region is not aligned well, unaligned region will be returned to LargeFree while splitAndAllocate() is called. Those regions won't match to any request to LargeFree until the neighbor region is returned to LargeFree and get merged with that. 1. Align 40k memory region A. Both start and end is aligned in 4k boundary. 2. realloc A to 36k + 8. shrinkLarge tries to split it in that size, B (36k +8) and C (4k - 8) 3. B's end is not aligned, but there's no practical issue. 4. On the other hand, C's start address is not aligned and sit in the LargeFree. It won't fit to any request because it's not aligned. 1808648 2 webkit-bug-importer 2021-10-25 16:03:18 -0700 <rdar://problem/84635991>