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Message-ID: <90298827-01f9-48dd-9a4c-7990105b4bf0@kernel.org>
Date: Fri, 8 Aug 2025 08:50:44 +0800
From: Chao Yu <chao@...nel.org>
To: Liao Yuanhong <liaoyuanhong@...o.com>, Jaegeuk Kim <jaegeuk@...nel.org>
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: Add bggc_block_io to adjust the priority of
BG_GC when issuing IO
On 2025/8/7 17:12, Liao Yuanhong wrote:
>
> On 8/7/2025 4:38 PM, Chao Yu wrote:
>> On 8/6/25 15:09, Liao Yuanhong wrote:
>>> Currently, we have encountered some issues while testing ZUFS. In
>>> situations near the storage limit (e.g., 50GB remaining), and after
>>> simulating fragmentation by repeatedly writing and deleting data, we found
>>> that application installation and startup tests conducted after idling for
>>> a few minutes take significantly longer several times that of traditional
>>> UFS. Tracing the operations revealed that the majority of I/Os were issued
>>> by background GC, which blocks normal I/O operations.
>>>
>>> Under normal circumstances, ZUFS indeed requires more background GC and
>>> employs a more aggressive GC strategy. However, I aim to find a way to
>>> minimize the impact on regular I/O operations under these near-limit
>>> conditions. To address this, I have introduced a bggc_block_io feature,
>>> which controls the prioritization of background GC in the presence of I/Os.
>>> This switch can be adjusted at the framework level to implement different
>>> strategies. If set to ALL_IO_PRIOR, all background GC operations will be
>>> skipped during active I/O issuance. The default option remains consistent
>>> with the current strategy, ensuring no change in behavior.
>>>
>>> Signed-off-by: Liao Yuanhong <liaoyuanhong@...o.com>
>>> ---
>>> Changes in v2:
>>> Non ZUFS can also be adjusted through this option.
>>> ---
>>> Documentation/ABI/testing/sysfs-fs-f2fs | 13 +++++++++++++
>>> fs/f2fs/f2fs.h | 18 +++++++++++-------
>>> fs/f2fs/super.c | 2 ++
>>> fs/f2fs/sysfs.c | 9 +++++++++
>>> 4 files changed, 35 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
>>> index bc0e7fefc39d..12fda11d4da5 100644
>>> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
>>> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
>>> @@ -883,3 +883,16 @@ Date: June 2025
>>> Contact: "Daeho Jeong" <daehojeong@...gle.com>
>>> Description: Control GC algorithm for boost GC. 0: cost benefit, 1: greedy
>>> Default: 1
>>> +
>>> +What: /sys/fs/f2fs/<disk>/bggc_block_io
>>> +Date: August 2025
>>> +Contact: "Liao Yuanhong" <liaoyuanhong@...o.com>
>>> +Description: Used to adjust the BG_GC priority when issuing IO, with a default value
>>> + of 1.
>> Default value is 2 if CONFIG_BLK_DEV_ZONED is off?
>>
>> Thanks,
>
> Sorry, I missed updating the description. Is it more reasonable to set the default value to 0 for versions that disable CONFIG_BLK_DEV_ZONED? If so, I will submit a new version to correct the description and initial value settings here. Thanks, Liao
Before this patch, the default behavior is something like ALL_IO_PRIOR?
What do you think of defining ALL_IO_PRIOR w/ 0, and use it by default?
Thanks,
>
>>> +
>>> + ================== =============================================
>>> + value description
>>> + bggc_block_io = 0 Prioritize background GC
>>> + bggc_block_io = 1 Stop background GC only when issuing read I/O
>>> + bggc_block_io = 2 Stop background GC when issuing I/O
>>> + ================== =============================================
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 46be7560548c..fe41b733fbc2 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -155,6 +155,12 @@ enum blkzone_allocation_policy {
>>> BLKZONE_ALLOC_PRIOR_CONV, /* Prioritize writing to conventional zones */
>>> };
>>> +enum bggc_block_io_policy {
>>> + BGGC_PRIOR,
>>> + READ_IO_PRIOR,
>>> + ALL_IO_PRIOR,
>>> +};
>>> +
>>> /*
>>> * An implementation of an rwsem that is explicitly unfair to readers. This
>>> * prevents priority inversion when a low-priority reader acquires the read lock
>>> @@ -1804,6 +1810,7 @@ struct f2fs_sb_info {
>>> spinlock_t dev_lock; /* protect dirty_device */
>>> bool aligned_blksize; /* all devices has the same logical blksize */
>>> unsigned int first_seq_zone_segno; /* first segno in sequential zone */
>>> + unsigned int bggc_block_io; /* For adjust the BG_GC priority when issuing IO */
>>> /* For write statistics */
>>> u64 sectors_written_start;
>>> @@ -2998,13 +3005,10 @@ static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
>>> if (sbi->gc_mode == GC_URGENT_HIGH)
>>> return true;
>>> - if (zoned_gc) {
>>> - if (is_inflight_read_io(sbi))
>>> - return false;
>>> - } else {
>>> - if (is_inflight_io(sbi, type))
>>> - return false;
>>> - }
>>> + if (sbi->bggc_block_io == READ_IO_PRIOR && is_inflight_read_io(sbi))
>>> + return false;
>>> + if (sbi->bggc_block_io == ALL_IO_PRIOR && is_inflight_io(sbi, type))
>>> + return false;
>>> if (sbi->gc_mode == GC_URGENT_MID)
>>> return true;
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index e16c4e2830c2..a21cecc5424e 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -4629,9 +4629,11 @@ 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_block_io = ALL_IO_PRIOR;
>>> #ifdef CONFIG_BLK_DEV_ZONED
>>> sbi->max_open_zones = UINT_MAX;
>>> sbi->blkzone_alloc_policy = BLKZONE_ALLOC_PRIOR_SEQ;
>>> + sbi->bggc_block_io = READ_IO_PRIOR;
>>> #endif
>>> for (i = 0; i < max_devices; i++) {
>>> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
>>> index f736052dea50..efea15209788 100644
>>> --- a/fs/f2fs/sysfs.c
>>> +++ b/fs/f2fs/sysfs.c
>>> @@ -674,6 +674,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
>>> sbi->blkzone_alloc_policy = t;
>>> return count;
>>> }
>>> +
>>> + if (!strcmp(a->attr.name, "bggc_block_io")) {
>>> + if (t < BGGC_PRIOR || t > ALL_IO_PRIOR)
>>> + return -EINVAL;
>>> + sbi->bggc_block_io = t;
>>> + return count;
>>> + }
>>> #endif
>>> #ifdef CONFIG_F2FS_FS_COMPRESSION
>>> @@ -1172,6 +1179,7 @@ F2FS_SBI_GENERAL_RW_ATTR(max_read_extent_count);
>>> #ifdef CONFIG_BLK_DEV_ZONED
>>> F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
>>> F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
>>> +F2FS_SBI_GENERAL_RW_ATTR(bggc_block_io);
>>> #endif
>>> F2FS_SBI_GENERAL_RW_ATTR(carve_out);
>>> F2FS_SBI_GENERAL_RW_ATTR(reserved_pin_section);
>>> @@ -1342,6 +1350,7 @@ static struct attribute *f2fs_attrs[] = {
>>> #ifdef CONFIG_BLK_DEV_ZONED
>>> ATTR_LIST(unusable_blocks_per_sec),
>>> ATTR_LIST(blkzone_alloc_policy),
>>> + ATTR_LIST(bggc_block_io),
>>> #endif
>>> #ifdef CONFIG_F2FS_FS_COMPRESSION
>>> ATTR_LIST(compr_written_block),
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