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Subject[PATCH 4/6] ftrace: simplify the calculation of page number for ftrace_page->records
Date
Based on the following two reasones, we could simplify the calculation:

- If the number after roundup count is not power of 2, we would
definitely have more than 1 empty page with a higher order.
- get_count_order() just return current order, so one lower order
could meet the requirement.

The calculation could be simplified by lower one order level when pages
are not power of 2.

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
---
kernel/trace/ftrace.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9021e16fa079..15fcfa16895d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3127,18 +3127,19 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs)
static int ftrace_allocate_records(struct ftrace_page *pg, int count)
{
int order;
- int cnt;
+ int pages, cnt;

if (WARN_ON(!count))
return -EINVAL;

- order = get_count_order(DIV_ROUND_UP(count, ENTRIES_PER_PAGE));
+ pages = DIV_ROUND_UP(count, ENTRIES_PER_PAGE);
+ order = get_count_order(pages);

/*
* We want to fill as much as possible. No more than a page
* may be empty.
*/
- while ((PAGE_SIZE << order) / ENTRY_SIZE >= count + ENTRIES_PER_PAGE)
+ if (!is_power_of_2(pages))
order--;

again:
--
2.20.1 (Apple Git-117)
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