[PATCH] fs: ratelimit __find_get_block_slow() failure message.

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Jan Kara <jack@suse.cz>, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Vyukov <dvyukov@google.com>,
	linux-fsdevel@vger.kernel.org,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: [PATCH] fs: ratelimit __find_get_block_slow() failure message.
Date: Fri, 11 Jan 2019 19:10:33 +0900	[thread overview]
Message-ID: <1547201433-10231-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> (raw)

When something let __find_get_block_slow() hit all_mapped path, it calls
printk() for 100+ times per a second. But there is no need to print same
message with such high frequency; it is just asking for stall warning, or
at least bloating log files.

  [  399.866302][T15342] __find_get_block_slow() failed. block=1, b_blocknr=8
  [  399.873324][T15342] b_state=0x00000029, b_size=512
  [  399.878403][T15342] device loop0 blocksize: 4096
  [  399.883296][T15342] __find_get_block_slow() failed. block=1, b_blocknr=8
  [  399.890400][T15342] b_state=0x00000029, b_size=512
  [  399.895595][T15342] device loop0 blocksize: 4096
  [  399.900556][T15342] __find_get_block_slow() failed. block=1, b_blocknr=8
  [  399.907471][T15342] b_state=0x00000029, b_size=512
  [  399.912506][T15342] device loop0 blocksize: 4096

This patch reduces frequency to approximately once per a second, in
addition to concatenating three lines into one. This patch uses plain
time_in_range() than __ratelimit(), for there is no need to allocate
space for debug objects in ratelimit_state.lock field.

  [  399.866302][T15342] __find_get_block_slow() failed. block=1, b_blocknr=8, b_state=0x00000029, b_size=512, device loop0 blocksize: 4096

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 fs/buffer.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 52d024b..3fc9167 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -200,6 +200,7 @@ void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 	struct buffer_head *head;
 	struct page *page;
 	int all_mapped = 1;
+	static unsigned long last;
 
 	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
 	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
@@ -227,15 +228,13 @@ void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 	 * file io on the block device and getblk.  It gets dealt with
 	 * elsewhere, don't buffer_error if we had some unmapped buffers
 	 */
-	if (all_mapped) {
-		printk("__find_get_block_slow() failed. "
-			"block=%llu, b_blocknr=%llu\n",
-			(unsigned long long)block,
-			(unsigned long long)bh->b_blocknr);
-		printk("b_state=0x%08lx, b_size=%zu\n",
-			bh->b_state, bh->b_size);
-		printk("device %pg blocksize: %d\n", bdev,
-			1 << bd_inode->i_blkbits);
+	if (all_mapped && !time_in_range(jiffies, last, last + HZ)) {
+		printk("__find_get_block_slow() failed. block=%llu, b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, device %pg blocksize: %d\n",
+		       (unsigned long long)block,
+		       (unsigned long long)bh->b_blocknr,
+		       bh->b_state, bh->b_size, bdev,
+		       1 << bd_inode->i_blkbits);
+		last = jiffies;
 	}
 out_unlock:
 	spin_unlock(&bd_mapping->private_lock);
-- 
1.8.3.1
