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Message-ID: <d7ce9dd9-e26f-44bc-8ccc-709ab598aa5c@vivo.com>
Date: Mon, 25 Aug 2025 12:02:40 +0800
From: Liao Yuanhong <liaoyuanhong@...o.com>
To: Chao Yu <chao@...nel.org>, Jaegeuk Kim <jaegeuk@...nel.org>,
"open list:F2FS FILE SYSTEM" <linux-f2fs-devel@...ts.sourceforge.net>,
open list <linux-kernel@...r.kernel.org>
Cc: liaoyuanhong@...o.com
Subject: Re: [PATCH v2] f2fs: Use allocate_section_policy to control write
priority in multi-devices setups
On 8/25/2025 11:56 AM, Chao Yu wrote:
> On 8/25/25 11:42, Liao Yuanhong wrote:
>> On 8/25/2025 11:10 AM, Chao Yu wrote:
>>> Yuanhong,
>>>
>>> On 8/20/25 16:21, Liao Yuanhong wrote:
>>>> 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@...o.com>
>>>> ---
>>>> Changes in v2:
>>>> - Updated the feature naming to better reflect its actual functionality.
>>>> - Appended patch description to clarify whether the usage should be
>>>> limited to multi-devices.
>>>> - Improved the code style.
>>>> - Fixed typo.
>>>> ---
>>>> Documentation/ABI/testing/sysfs-fs-f2fs | 22 ++++++++++++++++++++++
>>>> fs/f2fs/f2fs.h | 8 ++++++++
>>>> fs/f2fs/gc.c | 5 +++++
>>>> fs/f2fs/segment.c | 18 +++++++++++++++++-
>>>> fs/f2fs/super.c | 4 ++++
>>>> fs/f2fs/sysfs.c | 18 ++++++++++++++++++
>>>> 6 files changed, 74 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
>>>> index ee3acc8c2cb8..b590809869ca 100644
>>>> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
>>>> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
>>>> @@ -911,3 +911,25 @@ Description: Used to adjust the BG_GC priority when pending IO, with a default v
>>>> bggc_io_aware = 1 skip background GC if there is pending read IO
>>>> bggc_io_aware = 2 don't aware IO for background GC
>>>> ================== ======================================================
>>>> +
>>>> +What: /sys/fs/f2fs/<disk>/allocate_section_hint
>>>> +Date: August 2025
>>>> +Contact: "Liao Yuanhong" <liaoyuanhong@...o.com>
>>>> +Description: Indicates the hint section between the first device and others in multi-devices
>>>> + setup. It defaults to the end of the first device in sections. For a single storage
>>>> + device, it defaults to the total number of sections. It can be manually set to match
>>>> + scenarios where multi-devices are mapped to the same dm device.
>>>> +
>>>> +What: /sys/fs/f2fs/<disk>/allocate_section_policy
>>>> +Date: August 2025
>>>> +Contact: "Liao Yuanhong" <liaoyuanhong@...o.com>
>>>> +Description: Controls write priority in multi-devices setups. A value of 0 means normal writing.
>>>> + A value of 1 prioritizes writing to devices before the allocate_section_hint. A value of 2
>>>> + prioritizes writing to devices after the allocate_section_hint. The default is 0.
>>>> +
>>>> + =========================== ==========================================================
>>>> + value description
>>>> + allocate_section_policy = 0 Normal writing
>>>> + allocate_section_policy = 1 Prioritize writing to section before allocate_section_hint
>>>> + allocate_section_policy = 2 Prioritize writing to section after allocate_section_hint
>>>> + =========================== ==========================================================
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index d6a49de1b7e9..5ce9bf6be462 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -162,6 +162,12 @@ enum bggc_io_aware_policy {
>>>> AWARE_NONE, /* don't aware IO for background GC */
>>>> };
>>>> +enum device_allocation_policy {
>>>> + ALLOCATE_FORWARD_NOHINT,
>>>> + ALLOCATE_FORWARD_WITHIN_HINT,
>>>> + ALLOCATE_FORWARD_FROM_HINT,
>>>> +};
>>>> +
>>>> /*
>>>> * An implementation of an rwsem that is explicitly unfair to readers. This
>>>> * prevents priority inversion when a low-priority reader acquires the read lock
>>>> @@ -1850,6 +1856,8 @@ struct f2fs_sb_info {
>>>> bool aligned_blksize; /* all devices has the same logical blksize */
>>>> unsigned int first_seq_zone_segno; /* first segno in sequential zone */
>>>> unsigned int bggc_io_aware; /* For adjust the BG_GC priority when pending IO */
>>>> + unsigned int allocate_section_hint; /* the boundary position between devices */
>>>> + unsigned int allocate_section_policy; /* determine the section writing priority */
>>>> /* For write statistics */
>>>> u64 sectors_written_start;
>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>> index 098e9f71421e..b57b8fd64747 100644
>>>> --- a/fs/f2fs/gc.c
>>>> +++ b/fs/f2fs/gc.c
>>>> @@ -2182,6 +2182,8 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
>>>> SM_I(sbi)->segment_count = (int)SM_I(sbi)->segment_count + segs;
>>>> MAIN_SEGS(sbi) = (int)MAIN_SEGS(sbi) + segs;
>>>> MAIN_SECS(sbi) += secs;
>>>> + if (sbi->allocate_section_hint > MAIN_SECS(sbi))
>>>> + sbi->allocate_section_hint = MAIN_SECS(sbi);
>>>> FREE_I(sbi)->free_sections = (int)FREE_I(sbi)->free_sections + secs;
>>>> FREE_I(sbi)->free_segments = (int)FREE_I(sbi)->free_segments + segs;
>>>> F2FS_CKPT(sbi)->user_block_count = cpu_to_le64(user_block_count + blks);
>>>> @@ -2189,6 +2191,9 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
>>>> if (f2fs_is_multi_device(sbi)) {
>>>> int last_dev = sbi->s_ndevs - 1;
>>>> + sbi->allocate_section_hint = FDEV(0).total_segments /
>>>> + SEGS_PER_SEC(sbi);
>>>> +
>>>> FDEV(last_dev).total_segments =
>>>> (int)FDEV(last_dev).total_segments + segs;
>>>> FDEV(last_dev).end_blk =
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 04b0a3c1804d..e0f6589c6a1c 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -2807,6 +2807,10 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
>>>> }
>>>> #endif
>>>> + if (sbi->allocate_section_policy == ALLOCATE_FORWARD_FROM_HINT &&
>>>> + hint < sbi->allocate_section_hint)
>>>> + hint = sbi->allocate_section_hint;
>>>> +
>>>> find_other_zone:
>>>> secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
>>>> @@ -2828,13 +2832,25 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
>>>> #endif
>>>> if (secno >= MAIN_SECS(sbi)) {
>>>> - secno = find_first_zero_bit(free_i->free_secmap,
>>>> + if (sbi->allocate_section_policy == ALLOCATE_FORWARD_FROM_HINT) {
>>>> + secno = find_next_zero_bit(free_i->free_secmap,
>>>> + MAIN_SECS(sbi), sbi->allocate_section_hint);
>>>> + if (secno >= MAIN_SECS(sbi))
>>>> + secno = find_first_zero_bit(free_i->free_secmap,
>>>> + MAIN_SECS(sbi));
>>>> + } else {
>>>> + secno = find_first_zero_bit(free_i->free_secmap,
>>>> MAIN_SECS(sbi));
>>>> + }
>>>> if (secno >= MAIN_SECS(sbi)) {
>>>> ret = -ENOSPC;
>>>> f2fs_bug_on(sbi, !pinning);
>>>> goto out_unlock;
>>>> }
>>>> + } else if (sbi->allocate_section_policy == ALLOCATE_FORWARD_WITHIN_HINT &&
>>>> + secno >= sbi->allocate_section_hint) {
>>>> + secno = find_first_zero_bit(free_i->free_secmap,
>>>> + MAIN_SECS(sbi));
>>> Will we hit "secno >= MAIN_SECS(sbi)" case here?
>>
>> Yes, there may be hit 'secno>=MAIN_SECS (sbi)' case, and I will fix this issue in
>>
>> the new version patch.
>>
>>>> }
>>>> segno = GET_SEG_FROM_SEC(sbi, secno);
>>>> zoneno = GET_ZONE_FROM_SEC(sbi, secno);
>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>> index 5aa9d650512d..fa38a3e6b9cd 100644
>>>> --- a/fs/f2fs/super.c
>>>> +++ b/fs/f2fs/super.c
>>>> @@ -3942,6 +3942,7 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
>>>> segs_per_sec = le32_to_cpu(raw_super->segs_per_sec);
>>>> secs_per_zone = le32_to_cpu(raw_super->secs_per_zone);
>>>> total_sections = le32_to_cpu(raw_super->section_count);
>>>> + sbi->allocate_section_hint = total_sections;
>>> What about assigning sbi->allocate_section_hint in anywhere else rather than
>>> in sanity_check_raw_super()?
>>
>>
>> You're right, it's not suitable to initialize sbi->allocate_section_hint here. I'll put it in
>>
>> init_sb_info() or f2fs_scan_devices().
>>
>>>> /* blocks_per_seg should be 512, given the above check */
>>>> blocks_per_seg = BIT(le32_to_cpu(raw_super->log_blocks_per_seg));
>>>> @@ -4713,6 +4714,7 @@ static int f2fs_scan_devices(struct f2fs_sb_info *sbi)
>>>> logical_blksize = bdev_logical_block_size(sbi->sb->s_bdev);
>>>> sbi->aligned_blksize = true;
>>>> sbi->bggc_io_aware = AWARE_ALL_IO;
>>>> + sbi->allocate_section_policy = ALLOCATE_FORWARD_NOHINT;
>>>> #ifdef CONFIG_BLK_DEV_ZONED
>>>> sbi->max_open_zones = UINT_MAX;
>>>> sbi->blkzone_alloc_policy = BLKZONE_ALLOC_PRIOR_SEQ;
>>>> @@ -4744,6 +4746,8 @@ static int f2fs_scan_devices(struct f2fs_sb_info *sbi)
>>>> SEGS_TO_BLKS(sbi,
>>>> FDEV(i).total_segments) - 1 +
>>>> le32_to_cpu(raw_super->segment0_blkaddr);
>>>> + sbi->allocate_section_hint = FDEV(i).total_segments /
>>>> + SEGS_PER_SEC(sbi);
>>>> } else {
>>>> FDEV(i).start_blk = FDEV(i - 1).end_blk + 1;
>>>> FDEV(i).end_blk = FDEV(i).start_blk +
>>>> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
>>>> index 1ffaf9e74ce9..81b99c2a02a9 100644
>>>> --- a/fs/f2fs/sysfs.c
>>>> +++ b/fs/f2fs/sysfs.c
>>>> @@ -889,6 +889,20 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
>>>> return count;
>>>> }
>>>> + if (!strcmp(a->attr.name, "allocate_section_hint")) {
>>>> + if (t < 0 || t > MAIN_SECS(sbi))
>>>> + return -EINVAL;
>>>> + sbi->allocate_section_hint = t;
>>> Will it race w/ resize_fs ioctl?
>>>
>>> Thanks,
>>
>> Does this mean that after executing resize_fs, the current allocate_section_hint value will
>>
>> not match the resized size? If so, I've handled the data update in update_fs_metadata().
>>
>> If not, what other areas might cause a conflict? Please let me know so I can address the
>>
>> issue immediately.
> I meant something like this:
>
> resize (cpu 0) sysfs (cpu 1)
> - MAIN_SECS(sbi) += secs;
> - if (sbi->allocate_section_hint > MAIN_SECS(sbi))
> sbi->allocate_section_hint = MAIN_SECS(sbi);
> - if (t < 0 || t > MAIN_SECS(sbi))
> : what if MAIN_SECS() has the old value before
> statement "MAIN_SECS(sbi) += secs;" since cache
> between cpu 0 & 1 may not the same unless you
> call barrier to flush cache? Not sure, we'd better
> to avoid such race case w/ a lock?
I understand your concern. I will investigate how to prevent this
situation. This will be addressed in the next version of the patch.
Thanks,
Liao
>>
>> Thanks,
>>
>> Liao
>>
>>>> + return count;
>>>> + }
>>>> +
>>>> + if (!strcmp(a->attr.name, "allocate_section_policy")) {
>>>> + if (t < ALLOCATE_FORWARD_NOHINT || t > ALLOCATE_FORWARD_FROM_HINT)
>>>> + return -EINVAL;
>>>> + sbi->allocate_section_policy = t;
>>>> + return count;
>>>> + }
>>>> +
>>>> *ui = (unsigned int)t;
>>>> return count;
>>>> @@ -1161,6 +1175,8 @@ F2FS_SBI_GENERAL_RW_ATTR(max_victim_search);
>>>> F2FS_SBI_GENERAL_RW_ATTR(migration_granularity);
>>>> F2FS_SBI_GENERAL_RW_ATTR(migration_window_granularity);
>>>> F2FS_SBI_GENERAL_RW_ATTR(dir_level);
>>>> +F2FS_SBI_GENERAL_RW_ATTR(allocate_section_hint);
>>>> +F2FS_SBI_GENERAL_RW_ATTR(allocate_section_policy);
>>>> #ifdef CONFIG_F2FS_IOSTAT
>>>> F2FS_SBI_GENERAL_RW_ATTR(iostat_enable);
>>>> F2FS_SBI_GENERAL_RW_ATTR(iostat_period_ms);
>>>> @@ -1398,6 +1414,8 @@ static struct attribute *f2fs_attrs[] = {
>>>> ATTR_LIST(max_read_extent_count),
>>>> ATTR_LIST(carve_out),
>>>> ATTR_LIST(reserved_pin_section),
>>>> + ATTR_LIST(allocate_section_hint),
>>>> + ATTR_LIST(allocate_section_policy),
>>>> NULL,
>>>> };
>>>> ATTRIBUTE_GROUPS(f2fs);
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