f2fs: Use allocate_section_policy to control write priority in multi-devices setups

Introduces two new sys nodes: allocate_section_hint and
allocate_section_policy. The allocate_section_hint identifies the boundary
between devices, measured in sections; it defaults to the end of the device
for single storage setups, and the end of the first device for multiple
storage setups. The allocate_section_policy determines the write strategy,
with a default value of 0 for normal sequential write strategy. A value of
1 prioritizes writes before the allocate_section_hint, while a value of 2
prioritizes writes after it.

This strategy addresses the issue where, despite F2FS supporting multiple
devices, SOC vendors lack multi-devices support (currently only supporting
zoned devices). As a workaround, multiple storage devices are mapped to a
single dm device. Both this workaround and the F2FS multi-devices solution
may require prioritizing writing to certain devices, such as a device with
better performance or when switching is needed due to performance
degradation near a device's end. For scenarios with more than two devices,
sort them at mount time to utilize this feature.

When using this feature with a single storage device, it has almost no
impact. However, for configurations where multiple storage devices are
mapped to the same dm device using F2FS, utilizing this feature can provide
some optimization benefits. Therefore, I believe it should not be limited
to just multi-devices usage.

Signed-off-by: Liao Yuanhong <liaoyuanhong@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 04b0a3c1804d..e4d71755a60f 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2774,6 +2774,8 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
 	unsigned int total_zones = MAIN_SECS(sbi) / sbi->secs_per_zone;
 	unsigned int hint = GET_SEC_FROM_SEG(sbi, *newseg);
 	unsigned int old_zoneno = GET_ZONE_FROM_SEG(sbi, *newseg);
+	unsigned int alloc_policy = sbi->allocate_section_policy;
+	unsigned int alloc_hint = sbi->allocate_section_hint;
 	bool init = true;
 	int i;
 	int ret = 0;
@@ -2807,6 +2809,21 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
 	}
 #endif
 
+	/*
+	 * Prevent allocate_section_hint from exceeding MAIN_SECS()
+	 * due to desynchronization.
+	 */
+	if (alloc_policy != ALLOCATE_FORWARD_NOHINT &&
+		alloc_hint > MAIN_SECS(sbi))
+		alloc_hint = MAIN_SECS(sbi);
+
+	if (alloc_policy == ALLOCATE_FORWARD_FROM_HINT &&
+		hint < alloc_hint)
+		hint = alloc_hint;
+	else if (alloc_policy == ALLOCATE_FORWARD_WITHIN_HINT &&
+			hint >= alloc_hint)
+		hint = 0;
+
 find_other_zone:
 	secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);