Re: [f2fs-dev] [PATCH v3] f2fs: fix to freeze GC and discard threads quickly

[Chao Yu <chao@kernel.org>]

On 2026/3/18 00:15, Daeho Jeong wrote:
> On Mon, Mar 16, 2026 at 6:56 PM Chao Yu <chao@kernel.org> wrote:
>>
>> On 2026/3/17 02:59, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@google.com>
>>>
>>> Suspend can fail if kernel threads do not freeze for a while.
>>> f2fs_gc and f2fs_discard threads can perform long-running operations
>>> that prevent them from reaching a freeze point in a timely manner.
>>>
>>> This patch adds explicit freezing checks in the following locations:
>>> 1. f2fs_gc: Added a check at the 'retry' label to exit the loop quickly
>>>      if freezing is requested, especially during heavy GC rounds.
>>> 2. __issue_discard_cmd: Added a 'suspended' flag to break both inner and
>>>      outer loops during discard command issuance if freezing is detected
>>>      after at least one command has been issued.
>>> 3. __issue_discard_cmd_orderly: Added a similar check for orderly discard
>>>      to ensure responsiveness.
>>>
>>> These checks ensure that the threads release locks safely and enter the
>>> frozen state.
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@google.com>
>>> ---
>>> v3: removed unnecessary suspended check
>>> v2: add freezing check in do_garbage_collect()
>>> ---
>>>    fs/f2fs/gc.c      | 10 ++++++++++
>>>    fs/f2fs/segment.c | 12 +++++++++++-
>>>    2 files changed, 21 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index 246496fbe5e5..2305f16cbabb 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -1889,12 +1889,18 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>>>                                sbi->next_victim_seg[gc_type] =
>>>                                        (cur_segno + 1 < sec_end_segno) ?
>>>                                        cur_segno + 1 : NULL_SEGNO;
>>> +
>>> +                     if (unlikely(freezing(current))) {
>>> +                             folio_put_refs(sum_folio, 2);
>>> +                             goto stop;
>>
>> Do we need to return EBUSY or something like that to indicate GC was
>> interrupted?
> 
> In the case of do_garbage_collect(), it is originally designed to stop before
> cleaning the entire section depending on the migration_window size or
> zoned GC operations, and it returns the count of segments reclaimed until
> that point. Therefore, returning the segment count reclaimed up to the
> moment of suspension seems more consistent with the existing behavior.
> If we return an error instead, the caller might miss the count of segments
> that were actually reclaimed.

It makes sense.

In addition, I think freezing(current) will only be true in context of gc thread,
for such background migration condition, we don't care the error number.

Thanks,

> 
>>
>>> +                     }
>>>                }
>>>    next_block:
>>>                folio_put_refs(sum_folio, 2);
>>>                segno = block_end_segno;
>>>        }
>>>
>>> +stop:
>>>        if (submitted)
>>>                f2fs_submit_merged_write(sbi, data_type);
>>>
>>> @@ -1968,6 +1974,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>>                goto stop;
>>>        }
>>>    retry:
>>> +     if (unlikely(freezing(current))) {
>>> +             ret = 0;
>>
>> Ditto.
> 
> For f2fs_gc(), if we return -EBUSY, the caller might perceive it as a
> situation where no more victims
> can be selected. This could lead to an issue where the idle time is
> incorrectly extended under the
> "no GC" condition.
> 
>>
>> Thanks,
>>
>>> +             goto stop;
>>> +     }
>>>        ret = __get_victim(sbi, &segno, gc_type, gc_control->one_time);
>>>        if (ret) {
>>>                /* allow to search victim from sections has pinned data */
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index e9b6d774b985..0c4fb4270185 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1606,6 +1606,9 @@ static void __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>>>                if (dc->state != D_PREP)
>>>                        goto next;
>>>
>>> +             if (*issued > 0 && unlikely(freezing(current)))
>>> +                     break;
>>> +
>>>                if (dpolicy->io_aware && !is_idle(sbi, DISCARD_TIME)) {
>>>                        io_interrupted = true;
>>>                        break;
>>> @@ -1645,6 +1648,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>        struct blk_plug plug;
>>>        int i, issued;
>>>        bool io_interrupted = false;
>>> +     bool suspended = false;
>>>
>>>        if (dpolicy->timeout)
>>>                f2fs_update_time(sbi, UMOUNT_DISCARD_TIMEOUT);
>>> @@ -1675,6 +1679,11 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>                list_for_each_entry_safe(dc, tmp, pend_list, list) {
>>>                        f2fs_bug_on(sbi, dc->state != D_PREP);
>>>
>>> +                     if (issued > 0 && unlikely(freezing(current))) {
>>> +                             suspended = true;
>>> +                             break;
>>> +                     }
>>> +
>>>                        if (dpolicy->timeout &&
>>>                                f2fs_time_over(sbi, UMOUNT_DISCARD_TIMEOUT))
>>>                                break;
>>> @@ -1694,7 +1703,8 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>>    next:
>>>                mutex_unlock(&dcc->cmd_lock);
>>>
>>> -             if (issued >= dpolicy->max_requests || io_interrupted)
>>> +             if (issued >= dpolicy->max_requests || io_interrupted ||
>>> +                                     suspended)
>>>                        break;
>>>        }
>>>
>>