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Message-ID: <12dc51f7-a765-4995-bf6d-8abe973f4ea1@kernel.org>
Date: Fri, 13 Jun 2025 16:49:07 +0800
From: Chao Yu <chao@...nel.org>
To: Zhiguo Niu <niuzhiguo84@...il.com>, wangzijie <wangzijie1@...or.com>
Cc: chao@...nel.org, jaegeuk@...nel.org, bo.wu@...o.com,
linux-kernel@...r.kernel.org, feng.han@...or.com,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: continue to allocate pinned section when
gc happens EAGAIN
On 2025/6/13 16:25, Zhiguo Niu wrote:
> wangzijie <wangzijie1@...or.com> 于2025年6月12日周四 20:38写道：
>>
>>> On 6/12/25 11:27, wangzijie wrote:
>>>> Wu Bo once mentioned a fallocate fail scenario in this link[1].
>>>> After commit 3fdd89b452c2("f2fs: prevent writing without fallocate()
>>>> for pinned files"), we cannot directly generate 4K size file and
>>>> pin it, but we can still generate non-segment aligned pinned file:
>>>>
>>>> touch test_file
>>>> ./f2fs_io pinfile set test_file
>>>> ./f2fs_io fallocate 0 0 8192 test_file
>>>> truncate -s 4096 test_file
>>>
>>> Well, shouldn't we avoid such case by adding check condition in setattr?
>>
>> Maybe like this?
>>
>> ---
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 6bd3de64f..2f6537d9c 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -1027,6 +1027,8 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>> struct inode *inode = d_inode(dentry);
>> struct f2fs_inode_info *fi = F2FS_I(inode);
>> int err;
>> + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> + block_t sec_blks = CAP_BLKS_PER_SEC(sbi);
>>
>> if (unlikely(f2fs_cp_error(F2FS_I_SB(inode))))
>> return -EIO;
>> @@ -1047,6 +1049,11 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>> !IS_ALIGNED(attr->ia_size,
>> F2FS_BLK_TO_BYTES(fi->i_cluster_size)))
>> return -EINVAL;
>> + if (f2fs_is_pinned_file(inode) &&
>> + attr->ia_size < i_size_read(inode) &&
>> + !IS_ALIGNED(attr->ia_size,
>> + F2FS_BLK_TO_BYTES(sec_blks)));
>> + return -EINVAL;
> Hi Chao and zijie,
> Excuse me ,I'm a bit confused about this:
> when a pin file size is not alinged with size of "section", it can not
> be truncated?
IMO, the pinned file can only be truncated to section-aligned size.
Thanks
> thanks！
>> }
>>
>> err = setattr_prepare(idmap, dentry, attr);
>> ---
>>
>>>>
>>>> By doing this, pin+fallocate failure(gc happens EAGAIN but f2fs shows
>>>> enough spare space) may occurs.
>>>>
>>>> From message in commit 2e42b7f817ac("f2fs: stop allocating pinned sections
>>>> if EAGAIN happens"), gc EAGAIN doesn't guarantee a free section, so we stop
>>>> allocating. But after commit 48ea8b200414 ("f2fs: fix to avoid panic once
>>>> fallocation fails for pinfile"), we have a way to avoid panic caused by
>>>> concurrent pinfile allocation run out of free section, so I think that we
>>>> can continue to allocate pinned section when gc happens EAGAIN. Even if we
>>>> don't have free section, f2fs_allocate_pinning_section() can fail with ENOSPC.
>>>
>>> What do you think of introduce /sys/fs/f2fs/<dev>/reserved_pin_section to
>>> tune @needed parameter of has_not_enough_free_secs()? If we configure it
>>> w/ zero, it can avoid f2fs_gc() before preallocation.
>>>
>>> ---
>>> fs/f2fs/f2fs.h | 3 +++
>>> fs/f2fs/file.c | 5 ++---
>>> fs/f2fs/super.c | 3 +++
>>> fs/f2fs/sysfs.c | 9 +++++++++
>>> 4 files changed, 17 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 785537576aa8..ffb15da570d7 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1731,6 +1731,9 @@ struct f2fs_sb_info {
>>> /* for skip statistic */
>>> unsigned long long skipped_gc_rwsem; /* FG_GC only */
>>>
>>> + /* free sections reserved for pinned file */
>>> + unsigned int reserved_pin_section;
>>> +
>>> /* threshold for gc trials on pinned files */
>>> unsigned short gc_pin_file_threshold;
>>> struct f2fs_rwsem pin_sem;
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 696131e655ed..a909f79db178 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1887,9 +1887,8 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
>>> }
>>> }
>>>
>>> - if (has_not_enough_free_secs(sbi, 0, f2fs_sb_has_blkzoned(sbi) ?
>>> - ZONED_PIN_SEC_REQUIRED_COUNT :
>>> - GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))) {
>>> + if (has_not_enough_free_secs(sbi, 0,
>>> + sbi->reserved_pin_section)) {
>>> f2fs_down_write(&sbi->gc_lock);
>>> stat_inc_gc_call_count(sbi, FOREGROUND);
>>> err = f2fs_gc(sbi, &gc_control);
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index 57adeff5ef25..48b97a95fd63 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -4975,6 +4975,9 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
>>> sbi->last_valid_block_count = sbi->total_valid_block_count;
>>> sbi->reserved_blocks = 0;
>>> sbi->current_reserved_blocks = 0;
>>> + sbi->reserved_pin_section = f2fs_sb_has_blkzoned(sbi) ?
>>> + ZONED_PIN_SEC_REQUIRED_COUNT :
>>> + GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi));
>>> limit_reserve_root(sbi);
>>> adjust_unusable_cap_perc(sbi);
>>>
>>> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
>>> index 75134d69a0bd..51be7ffb38c5 100644
>>> --- a/fs/f2fs/sysfs.c
>>> +++ b/fs/f2fs/sysfs.c
>>> @@ -824,6 +824,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
>>> return count;
>>> }
>>>
>>> + if (!strcmp(a->attr.name, "reserved_pin_section")) {
>>> + if (t > GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))
>>> + return -EINVAL;
>>> + *ui = (unsigned int)t;
>>> + return count;
>>> + }
>>> +
>>> *ui = (unsigned int)t;
>>>
>>> return count;
>>> @@ -1130,6 +1137,7 @@ F2FS_SBI_GENERAL_RO_ATTR(unusable_blocks_per_sec);
>>> F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
>>> #endif
>>> F2FS_SBI_GENERAL_RW_ATTR(carve_out);
>>> +F2FS_SBI_GENERAL_RW_ATTR(reserved_pin_section);
>>>
>>> /* STAT_INFO ATTR */
>>> #ifdef CONFIG_F2FS_STAT_FS
>>> @@ -1323,6 +1331,7 @@ static struct attribute *f2fs_attrs[] = {
>>> ATTR_LIST(last_age_weight),
>>> ATTR_LIST(max_read_extent_count),
>>> ATTR_LIST(carve_out),
>>> + ATTR_LIST(reserved_pin_section),
>>> NULL,
>>> };
>>> ATTRIBUTE_GROUPS(f2fs);
>>> --
>>> 2.49.0
>>
>> I think it's a good way to solve this problem. Thank you!
>>
>>
>>>>
>>>> [1] https://lore.kernel.org/linux-f2fs-devel/20231030094024.263707-1-bo.wu@vivo.com/t/#u
>>>>
>>>> Signed-off-by: wangzijie <wangzijie1@...or.com>
>>>> ---
>>>> fs/f2fs/file.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 6bd3de64f..05c80d2b5 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -1859,7 +1859,7 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
>>>> f2fs_down_write(&sbi->gc_lock);
>>>> stat_inc_gc_call_count(sbi, FOREGROUND);
>>>> err = f2fs_gc(sbi, &gc_control);
>>>> - if (err && err != -ENODATA) {
>>>> + if (err && err != -ENODATA && err != -EAGAIN) {
>>>> f2fs_up_write(&sbi->pin_sem);
>>>> goto out_err;
>>>> }
>>>
>>>
>>>
>>> _______________________________________________
>>> Linux-f2fs-devel mailing list
>>> Linux-f2fs-devel@...ts.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>
>>
>>
>> _______________________________________________
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>> Linux-f2fs-devel@...ts.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>
>
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