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

Chao Yu
2026-03-12T01:27:14Z

On 2026/3/12 00:00, Daeho Jeong wrote:
> On Wed, Mar 11, 2026 at 7:59 AM Chao Yu <chao@kernel.org> wrote:
>>
>> On 2026/3/11 04:49, 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>
>>> ---
>>> fs/f2fs/gc.c | 4 ++++
>>> fs/f2fs/segment.c | 14 ++++++++++++--
>>> 2 files changed, 16 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index 981eac629fe9..fdc3366c4db3 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -1962,6 +1962,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>> goto stop;
>>> }
>>> retry:
>>> + if (unlikely(freezing(current))) {
>>> + ret = 0;
>>> + goto stop;
>>> + }
>>
>> Do we need to check freezing() during multiple segments migration?
>> especially in large section, e.g. zufs case.
>
> Otherwise, we can't meet the 1 second suspend requirement for Android.
> This logic mainly targets zufs proactive GC cases.
> Plus, aren't the remaining segments in the section the next victims of
> GC for the next round?

Sorry, I didn't get the point, could you please explain more about your concern?

Actually, what I mean is if we missed freezeing() check condition in f2fs_gc(),
in do_garbage_collection(), after we migrated one segment of section, and before
migrate next segment in section, we can check freezing() condition at this time?

I meant maybe we can add more check spots in do_garbage_collection().

Thanks,

>
>>
>>> 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..a6c82ab28288 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;
>>> @@ -1694,11 +1703,12 @@ 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;
>>> }
>>>
>>> - if (dpolicy->type == DPOLICY_UMOUNT && issued) {
>>> + if (dpolicy->type == DPOLICY_UMOUNT && issued && !suspended) {
>>
>> If we're umounting data partition, it doesn't need to consider suspend?
>
> Makes sense.
>
>>
>> Thanks,
>>
>>> __wait_all_discard_cmd(sbi, dpolicy);
>>> goto retry;
>>> }
>>