[PATCH 1/2] perf: Allow non-contiguous AUX buffer pages via PMU capability

[Yabin Cui <yabinc@google.com>]

For PMUs like ARM ETM/ETE, contiguous AUX buffers are unnecessary
and increase memory fragmentation.

This patch introduces PERF_PMU_CAP_AUX_NON_CONTIGUOUS_PAGES, allowing
PMUs to request non-contiguous pages for their AUX buffers.

Signed-off-by: Yabin Cui <yabinc@google.com>
---
 include/linux/perf_event.h  | 1 +
 kernel/events/ring_buffer.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0069ba6866a4..26ca35d6a9f2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -301,6 +301,7 @@ struct perf_event_pmu_context;
 #define PERF_PMU_CAP_AUX_OUTPUT			0x0080
 #define PERF_PMU_CAP_EXTENDED_HW_TYPE		0x0100
 #define PERF_PMU_CAP_AUX_PAUSE			0x0200
+#define PERF_PMU_CAP_AUX_NON_CONTIGUOUS_PAGES	0x0400
 
 /**
  * pmu::scope
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 5130b119d0ae..87f42f4e8edc 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -710,6 +710,12 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
 		max_order = ilog2(nr_pages);
 		watermark = 0;
 	}
+	/*
+	 * When the PMU doesn't prefer contiguous AUX buffer pages, favor
+	 * low-order allocations to reduce memory fragmentation.
+	 */
+	if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NON_CONTIGUOUS_PAGES)
+		max_order = 0;
 
 	/*
 	 * kcalloc_node() is unable to allocate buffer if the size is larger
-- 
2.49.0.805.g082f7c87e0-goog