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

[Chao Yu]

On 2026/3/12 00:00, Daeho Jeong wrote:
> On Wed, Mar 11, 2026 at 7:59 AM Chao Yu <chao@xxxxxxxxxx> wrote:
> > On 2026/3/11 04:49, Daeho Jeong wrote:
> > > From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>
> > > ---
> > >    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;
> > >        }