On Tue, Aug 12, 2025 at 4:14 AM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > On Mon, 11 Aug 2025 at 23:13, Joanne Koong <joannelkoong@xxxxxxxxx> wrote: > > > > On Mon, Aug 11, 2025 at 1:43 PM Joanne Koong <joannelkoong@xxxxxxxxx> wrote: > > > > > > Large folios are only enabled if the writeback cache isn't on. > > > (Strictlimiting needs to be turned off if the writeback cache is used in > > > conjunction with large folios, else this tanks performance.) > > Is there an explanation somewhere about the writeback cache vs. > strictlimit issue? There's not much documentation about how strictlimit affects writeback but from the balance dirty pages code, my understanding is that with strictlimit on, the dirty throttle control uses the wb counters/limits instead of the global ones and calculates stuff like the setpoint and position ratio more conservatively, which leads to more eager io throttling. This rfc patchset [1] is meant to help but it won't help workloads that do lots of large sequential writes. Experimentally, with strictlimiting on and the writeback cache used with large folios, I saw around a 25 to 50% hit in throughput but with strictlimiting disabled, there was around a 12% to 15% improvement. (It'd also be great if others have time to confirm these benchmarks on their systems to make sure they're also seeing the same percentage improvements on their machines) [1] https://lore.kernel.org/linux-fsdevel/20250801002131.255068-1-joannelkoong@xxxxxxxxx/T/#t Thanks, Joanne > > Thanks, > Miklos
