Re: [PATCH] mm: khugepaged: make scan loops suspend aware

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Hi Sergey,

On 2/11/26 10:59 AM, Sergey Senozhatsky wrote:
> A number of khugepaaged's loops, e.g. khugepaged_scan_mm_slot(),
> are time unbound, which can become problematic during system
> suspend:
> 
> PM: suspend entry (s2idle)
> Filesystems sync: 0.003 seconds
> Freezing user space processes
> Freezing user space processes completed (elapsed 0.003 seconds)
> OOM killer disabled.
> Freezing remaining freezable tasks
> Freezing remaining freezable tasks failed after 20.004 seconds (1 tasks refusing to freeze, wq_busy=0):
> task:khugepaged      state:D stack:0     pid:1345  ppid:2      flags:0x00004000
> Call Trace:
>   <TASK>
>   schedule+0x523/0x16a0
>   schedule_timeout+0x23b/0x6e0
>   io_schedule_timeout+0x3f/0x80
>   wait_for_completion_io_timeout+0xe4/0x170
>   submit_bio_wait+0x79/0xc0
>   swap_readpage+0x150/0x2d0
>   swap_cluster_readahead+0x3be/0x750
>   shmem_swapin+0xa7/0x100
>   shmem_swapin_folio+0xcd/0x2e0
>   shmem_get_folio+0x237/0x580
>   collapse_file+0x247/0x1280
>   hpage_collapse_scan_file+0x26e/0x380
>   khugepaged+0x43b/0x810
>   kthread+0xfb/0x120
>   </TASK>
> 
> Make hpage_collapse_test_exit_or_disable() suspend aware so
> that khugepaaged's scan loops can terminate in a timely manner
> and let system enter the sleep state.
> 
> Co-developed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---

I just provided some sample code. Please make sure your patch can be 
built before submitting a formal patch.

Obviously, you should also modify the callers to pass in the 'cc' pointer.

>   mm/khugepaged.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index eff9e3061925..9b3201fb6840 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -392,10 +392,18 @@ static inline int hpage_collapse_test_exit(struct mm_struct *mm)
>   	return atomic_read(&mm->mm_users) == 0;
>   }
>   
> -static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm)
> +static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm,
> +						struct collapse_control *cc)
>   {
> +	bool was_frozen = false;
> +
> +	if (cc->is_khugepaged &&
> +	    unlikely(kthread_freezable_should_stop(&was_frozen)))
> +		return 1;
> +
>   	return hpage_collapse_test_exit(mm) ||
> -		mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm);
> +		mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) ||
> +		was_frozen;
>   }
>   
>   static bool hugepage_pmd_enabled(void)