linux-kernel - [for-linus][PATCH 12/15] ftrace: Simplify the calculation of page number for ftrace

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Date:   Tue, 06 Oct 2020 10:34:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>
Subject: [for-linus][PATCH 12/15] ftrace: Simplify the calculation of page number for
 ftrace_page->records

From: Wei Yang <richard.weiyang@...ux.alibaba.com>

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.

Link: https://lkml.kernel.org/r/20200831031104.23322-5-richard.weiyang@linux.alibaba.com

Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 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 c51a91aea1fd..c3be18b4f27b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3129,18 +3129,19 @@ 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:
-- 
2.28.0