f2fs: Add the 'whint_mode' mount option to f2fs documentation

Signed-off-by: Hyunchul Lee <cheol.lee@lge.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
[Jaegeuk Kim: Add the write-hint policy in f2fs doc.]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.txt

@@ -174,6 +174,12 @@ offgrpjquota           Turn off group journelled quota.
 offprjjquota           Turn off project journelled quota.
 quota                  Enable plain user disk quota accounting.
 noquota                Disable all plain disk quota option.
+whint_mode=%s          Control which write hints are passed down to block
+                       layer. This supports "off", "user-based", and
+                       "fs-based".  In "off" mode (default), f2fs does not pass
+                       down hints. In "user-based" mode, f2fs tries to pass
+                       down hints given by users. And in "fs-based" mode, f2fs
+                       passes down hints with its policy.
 
 ================================================================================
 DEBUGFS ENTRIES
@@ -611,3 +617,63 @@ algorithm.
 In order to identify whether the data in the victim segment are valid or not,
 F2FS manages a bitmap. Each bit represents the validity of a block, and the
 bitmap is composed of a bit stream covering whole blocks in main area.
+
+Write-hint Policy
+-----------------
+
+1) whint_mode=off. F2FS only passes down WRITE_LIFE_NOT_SET.
+
+2) whint_mode=user-based. F2FS tries to pass down hints given by
+users.
+
+User                  F2FS                     Block
+----                  ----                     -----
+                      META                     WRITE_LIFE_NOT_SET
+                      HOT_NODE                 "
+                      WARM_NODE                "
+                      COLD_NODE                "
+*ioctl(COLD)          COLD_DATA                WRITE_LIFE_EXTREME
+*extension list       "                        "
+
+-- buffered io
+WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
+WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
+WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
+WRITE_LIFE_NONE       "                        "
+WRITE_LIFE_MEDIUM     "                        "
+WRITE_LIFE_LONG       "                        "
+
+-- direct io
+WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
+WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
+WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
+WRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
+WRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
+WRITE_LIFE_LONG       "                        WRITE_LIFE_LONG
+
+3) whint_mode=fs-based. F2FS passes down hints with its policy.
+
+User                  F2FS                     Block
+----                  ----                     -----
+                      META                     WRITE_LIFE_MEDIUM;
+                      HOT_NODE                 WRITE_LIFE_NOT_SET
+                      WARM_NODE                "
+                      COLD_NODE                WRITE_LIFE_NONE
+ioctl(COLD)           COLD_DATA                WRITE_LIFE_EXTREME
+extension list        "                        "
+
+-- buffered io
+WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
+WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
+WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_LONG
+WRITE_LIFE_NONE       "                        "
+WRITE_LIFE_MEDIUM     "                        "
+WRITE_LIFE_LONG       "                        "
+
+-- direct io
+WRITE_LIFE_EXTREME    COLD_DATA                WRITE_LIFE_EXTREME
+WRITE_LIFE_SHORT      HOT_DATA                 WRITE_LIFE_SHORT
+WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
+WRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
+WRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
+WRITE_LIFE_LONG       "                        WRITE_LIFE_LONG