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Subject: [f2fs-dev] [PATCH] f2fs: change write_hint for hot/warm nodes
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Sender: Daejun Park <daejun7.park@samsung.com>
From:   Daejun Park <daejun7.park@samsung.com>
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        "chao@kernel.org" <chao@kernel.org>
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        SEUNGUK SHIN <seunguk.shin@samsung.com>,
        Sang-yoon Oh <sangyoon.oh@samsung.com>,
        Sung-Jun Park <sungjun07.park@samsung.com>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        Daejun Park <daejun7.park@samsung.com>,
        Jinyoung CHOI <j-young.choi@samsung.com>,
        Jieon Seol <jieon.seol@samsung.com>,
        Mankyu PARK <manq.park@samsung.com>,
        Jaemyung Lee <jaemyung.lee@samsung.com>,
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Message-ID: <20201103064039epcms2p30ecac0e7cefff0d50745f2e2e61ce38e@epcms2p3>
Date:   Tue, 03 Nov 2020 15:40:39 +0900
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From 818a76a9aee5bf225565264274d211edb07bae7d Mon Sep 17 00:00:00 2001
From: Daejun Park <daejun7.park@samsung.com>
Date: Tue, 3 Nov 2020 15:30:26 +0900


In the fs-based mode of F2FS, the mapping of hot/warm node to
WRITE_LIFE_NOT_SET should be changed to WRITE_LIFE_SHORT.

As a result of analyzing the write pattern of f2fs using real workload,
hot/warm nodes have high update ratio close to hot data.[*]
However, F2FS passes write hints for hot/warm nodes as WRITE_LIFE_NOT_SET.

Furthermore, WRITE_LIFE_NOT_SET is a default value of write hint when it is
not provided from the file system.
In storage, write_hint is used to distinguish streams (e.g. NVMe).
So, the hot/warm node of F2FS is not distinguished from other write_hints,
which can make the wrong stream seperation.

* Liang, Yu, et al. "An empirical study of F2FS on mobile devices." 2017
IEEE 23rd International Conference on Embedded and Real-Time Computing
Systems and Applications (RTCSA).

Signed-off-by: Daejun Park <daejun7.park@samsung.com>
---
 fs/f2fs/segment.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 1596502f7375..7b42bb10c6c3 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -3208,7 +3208,7 @@ enum rw_hint f2fs_io_type_to_rw_hint(struct f2fs_sb_info *sbi,
 				return WRITE_LIFE_EXTREME;
 		} else if (type == NODE) {
 			if (temp == WARM || temp == HOT)
-				return WRITE_LIFE_NOT_SET;
+				return WRITE_LIFE_SHORT;
 			else if (temp == COLD)
 				return WRITE_LIFE_NONE;
 		} else if (type == META) {
-- 
2.25.1