74af7fc603
This change makes it so that the GC pacer's trigger ratio can never fall below 0.6. Upcoming changes to the allocator make it significantly more scalable and thus much faster in certain cases, creating a large gap between the performance of allocation and scanning. The consequence of this is that the trigger ratio can drop very low (0.07 was observed) in order to drop GC utilization. A low trigger ratio like this results in a high amount of black allocations, which causes the live heap to appear larger, and thus the heap, and RSS, grows to a much higher stable point. This change alleviates the problem by placing a lower bound on the trigger ratio. The expected (and confirmed) effect of this is that utilization in certain scenarios will no longer converge to the expected 25%, and may go higher. As a result of this artificially high trigger ratio, more time will also be spent doing GC assists compared to dedicated mark workers, since the GC will be on for an artifically short fraction of time (artificial with respect to the pacer). The biggest concern of this change is that allocation latency will suffer as a result, since there will now be more assists. But, upcoming changes to the allocator reduce the latency enough to outweigh the expected increase in latency from this change, without the blowup in RSS observed from the changes to the allocator. Updates #35112. Change-Id: Idd7c94fa974d0de673304c4397e716e89bfbf09b Reviewed-on: https://go-review.googlesource.com/c/go/+/200439 Reviewed-by: Austin Clements <austin@google.com> |
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