Re: [PATCH 0/1] bcache: reduce front IO latency during GC

On Mon, Apr 14, 2025 at 03:44:03PM -0700, Robert Pang wrote:
> In performance benchmarks on disks with bcache using the Linux 6.6 kernel, we
> observe noticeable IO latency increase during btree garbage collection. The
> increase ranges from high tens to hundreds of milliseconds, depending on the
> size of the cache device. Further investigation reveals that it is the same
> issue reported in [1], where the large number of nodes processed in each
> incremental GC cycle causes the front IO latency.
> 
> Building upon the approach suggested in [1], this patch decomposes the
> incremental GC process into more but smaller cycles. In contrast to [1], this
> implementation adopts a simpler strategy by setting a lower limit of 10 nodes
> per cycle to reduce front IO delay and introducing a fixed 10ms sleep per cycle
> when front IO is in progress. Furthermore, when garbage collection statistics
> are available, the number of nodes processed per cycle is dynamically rescaled
> based on the average GC frequency to ensure GC completes well within the next
> subsequent scheduled interval.
> 
> Testing with a 750GB NVMe cache and 256KB bucket size using the following fio
> configuration demonstrates that our patch reduces front IO latency during GC
> without significantly increasing GC duration.

Have you been looking at bcachefs yet? It solves all the latency issues
in bcache.