On Tue, Jan 17, 2023 at 12:31 AM Jaewon Kim <jaewon31.kim@xxxxxxxxxxx> wrote: > > Using order 4 pages would be helpful for many IOMMUs, but it could spend > > quite much time in page allocation perspective. > > > > The order 4 allocation with __GFP_RECLAIM may spend much time in > > reclaim and compation logic. __GFP_NORETRY also may affect. These cause > > unpredictable delay. > > > > To get reasonable allocation speed from dma-buf system heap, use > > HIGH_ORDER_GFP for order 4 to avoid reclaim. Thanks for sharing this! The case where the allocation gets stuck behind reclaim under pressure does sound undesirable, but I'd be a bit hesitant to tweak numbers that have been used for a long while (going back to ion) without a bit more data. It might be good to also better understand the tradeoff of potential on-going impact to performance from using low order pages when the buffer is used. Do you have any details like or tests that you could share to help ensure this won't impact other users? TJ: Do you have any additional thoughts on this? thanks -john
