051809e352
This extends the sweeper to free workbufs back to the heap between GC cycles, allowing this memory to be reused for GC'd allocations or eventually returned to the OS. This helps for applications that have high peak heap usage relative to their regular heap usage (for example, a high-memory initialization phase). Workbuf memory is roughly proportional to heap size and since we currently never free workbufs, it's proportional to *peak* heap size. By freeing workbufs, we can release and reuse this memory for other purposes when the heap shrinks. This is somewhat complicated because this costs ~1–2 µs per workbuf span, so for large heaps it's too expensive to just do synchronously after mark termination between starting the world and dropping the worldsema. Hence, we do it asynchronously in the sweeper. This adds a list of "free" workbuf spans that can be returned to the heap. GC moves all workbuf spans to this list after mark termination and the background sweeper drains this list back to the heap. If the sweeper doesn't finish, that's fine, since getempty can directly reuse any remaining spans to allocate more workbufs. Performance impact is negligible. On the x/benchmarks, this reduces GC-bytes-from-system by 6–11%. Fixes #19325. Change-Id: Icb92da2196f0c39ee984faf92d52f29fd9ded7a8 Reviewed-on: https://go-review.googlesource.com/38582 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> |
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