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

Daeho Jeong
2026-03-11T16:00:14Z

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?

>
> > 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;
> > }
>