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 <[email protected]> Signed-off-by: Alexander Shishkin <[email protected]> --- kernel/events/ring_buffer.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 9c01d531ee..1c892fa034 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -472,7 +472,10 @@ 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); -- 2.4.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
