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authorAlexander Shishkin <alexander.shishkin@linux.intel.com>2015-07-28 09:00:04 +0300
committerIngo Molnar <mingo@kernel.org>2015-08-12 11:43:20 +0200
commitc2ad6b51efc5f27d70ce952decd2a15679b83600 (patch)
treea459e9e5f988ea348973af04c31e25ee37bb35e0
parent19b3340cf58d14decf2898fc795cc2b1fa49e79e (diff)
downloadlinux-c2ad6b51efc5f27d70ce952decd2a15679b83600.tar.bz2
perf/ring-buffer: Clarify the use of page::private for high-order AUX allocations
A question [1] was raised about the use of page::private in AUX buffer allocations, so let's add a clarification about its intended use. The private field and flag are used by perf's rb_alloc_aux() path to tell the pmu driver the size of each high-order allocation, so that the driver can program those appropriately into its hardware. This only matters for PMUs that don't support hardware scatter tables. Otherwise, every page in the buffer is just a page. This patch adds a comment about the private field to the AUX buffer allocation path. [1] http://marc.info/?l=linux-kernel&m=143803696607968 Reported-by: Mathieu Poirier <mathieu.poirier@linaro.org> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1438063204-665-1-git-send-email-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/events/ring_buffer.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index c8aa3f75bc4d..182bc30899d5 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -437,7 +437,10 @@ static struct page *rb_alloc_aux_page(int node, int order)
if (page && order) {
/*
- * Communicate the allocation size to the driver
+ * Communicate the allocation size to the driver:
+ * if we managed to secure a high-order allocation,
+ * set its first page's private to this order;
+ * !PagePrivate(page) means it's just a normal page.
*/
split_page(page, order);
SetPagePrivate(page);