linux-kernel - [PATCH 5.2 102/215] f2fs: fix is

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Message-Id: <20190729190756.728874297@linuxfoundation.org>
Date:   Mon, 29 Jul 2019 21:21:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sahitya Tummala <stummala@...eaurora.org>,
        Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.2 102/215] f2fs: fix is_idle() check for discard type

[ Upstream commit 56659ce838456c6f2315ce8a4bd686ac4b23e9d1 ]

The discard thread should issue upto dpolicy->max_requests at once
and wait for all those discard requests at once it reaches
dpolicy->max_requests. It should then sleep for dpolicy->min_interval
timeout before issuing the next batch of discard requests. But in the
current code of is_idle(), it checks for dcc_info->queued_discard and
aborts issuing the discard batch of max_requests. This
dcc_info->queued_discard will be true always once one discard command
is issued.

It is thus resulting into this type of discard request pattern -

- Issue discard request#1
- is_idle() returns false, discard thread waits for request#1 and then
  sleeps for min_interval 50ms.
- Issue discard request#2
- is_idle() returns false, discard thread waits for request#2 and then
  sleeps for min_interval 50ms.
- and so on for all other discard requests, assuming f2fs is idle w.r.t
  other conditions.

With this fix, the pattern will look like this -

- Issue discard request#1
- Issue discard request#2
  and so on upto max_requests of 8
- Issue discard request#8
- wait for min_interval 50ms.

Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
Reviewed-by: Chao Yu <yuchao0@...wei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/f2fs/f2fs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9e6721e15b24..cbdc2f88a98c 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2204,7 +2204,7 @@ static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
 		get_pages(sbi, F2FS_DIO_WRITE))
 		return false;
 
-	if (SM_I(sbi) && SM_I(sbi)->dcc_info &&
+	if (type != DISCARD_TIME && SM_I(sbi) && SM_I(sbi)->dcc_info &&
 			atomic_read(&SM_I(sbi)->dcc_info->queued_discard))
 		return false;
 
-- 
2.20.1