On Thu, Feb 9, 2023 at 9:03 PM Jaewon Kim <jaewon31.kim@xxxxxxxxxxx> wrote:
>
> >Using order 4 pages would be helpful for IOMMUs mapping, but trying to get order 4 pages could spend quite much time in the page allocation.
> >From the perspective of responsiveness, the deterministic memory allocation speed, I think, is quite important.
> >
> >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. And let me remove meaningless __GFP_COMP for order 0.
> >
> >According to my tests, order 4 with MID_ORDER_GFP could get more number of order 4 pages but the elapsed times could be very slow.
> >
> > time order 8 order 4 order 0
> > 584 usec 0 160 0
> > 28,428 usec 0 160 0
> > 100,701 usec 0 160 0
> > 76,645 usec 0 160 0
> > 25,522 usec 0 160 0
> > 38,798 usec 0 160 0
> > 89,012 usec 0 160 0
> > 23,015 usec 0 160 0
> > 73,360 usec 0 160 0
> > 76,953 usec 0 160 0
> > 31,492 usec 0 160 0
> > 75,889 usec 0 160 0
> > 84,551 usec 0 160 0
> > 84,352 usec 0 160 0
> > 57,103 usec 0 160 0
> > 93,452 usec 0 160 0
> >
> >If HIGH_ORDER_GFP is used for order 4, the number of order 4 could be decreased but the elapsed time results were quite stable and fast enough.
> >
> > time order 8 order 4 order 0
> > 1,356 usec 0 155 80
> > 1,901 usec 0 11 2384
> > 1,912 usec 0 0 2560
> > 1,911 usec 0 0 2560
> > 1,884 usec 0 0 2560
> > 1,577 usec 0 0 2560
> > 1,366 usec 0 0 2560
> > 1,711 usec 0 0 2560
> > 1,635 usec 0 28 2112
> > 544 usec 10 0 0
> > 633 usec 2 128 0
> > 848 usec 0 160 0
> > 729 usec 0 160 0
> > 1,000 usec 0 160 0
> > 1,358 usec 0 160 0
> > 2,638 usec 0 31 2064
> >
> >Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
> >---
> > drivers/dma-buf/heaps/system_heap.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> >index e8bd10e60998..920db302a273 100644
> >--- a/drivers/dma-buf/heaps/system_heap.c
> >+++ b/drivers/dma-buf/heaps/system_heap.c
> >@@ -41,12 +41,11 @@ struct dma_heap_attachment {
> > bool mapped;
> > };
> >
> >-#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO | __GFP_COMP) -#define MID_ORDER_GFP (LOW_ORDER_GFP | __GFP_NOWARN)
> >+#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO)
> > #define HIGH_ORDER_GFP (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
> > | __GFP_NORETRY) & ~__GFP_RECLAIM) \
> > | __GFP_COMP)
> >-static gfp_t order_flags[] = {HIGH_ORDER_GFP, MID_ORDER_GFP, LOW_ORDER_GFP};
> >+static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP,
> >+LOW_ORDER_GFP};
> > /*
> > * The selection of the orders used for allocation (1MB, 64K, 4K) is designed
> > * to match with the sizes often found in IOMMUs. Using order 4 pages instead
> >--
> >2.17.1
> >
> >
>
> added John Stultz <jstultz@xxxxxxxxxx>
Sorry for the delay!
Reviewed-by: John Stultz <jstultz@xxxxxxxxxx>
thanks
-john
