Re: [PATCH v5] mm: shrink skip folio mapped by an exiting process

[zhiguojiang <justinjiang@vivo.com>]

在 2024/7/8 20:41, Barry Song 写道:
>
>
> zhiguojiang <justinjiang@vivo.com> 于 2024年7月9日周二 00:25写道：
>
>
>
>     在 2024/7/8 20:17, zhiguojiang 写道:
>     >
>     >
>     > 在 2024/7/8 19:02, Barry Song 写道:
>     >> On Mon, Jul 8, 2024 at 9:04 PM Zhiguo Jiang <justinjiang@vivo.com>
>     >> wrote:
>     >>> The releasing process of the non-shared anonymous folio mapped
>     >>> solely by
>     >>> an exiting process may go through two flows: 1) the anonymous
>     folio is
>     >>> firstly is swaped-out into swapspace and transformed into a
>     swp_entry
>     >>> in shrink_folio_list; 2) then the swp_entry is released in the
>     process
>     >>> exiting flow. This will increase the cpu load of releasing a
>     non-shared
>     >>> anonymous folio mapped solely by an exiting process, because
>     the folio
>     >>> go through swap-out and the releasing the swapspace and swp_entry.
>     >>>
>     >>> When system is low memory, it is more likely to occur, because
>     more
>     >>> backend applidatuions will be killed.
>     >>>
>     >>> The modification is that shrink skips the non-shared anonymous
>     folio
>     >>> solely mapped by an exting process and the folio is only released
>     >>> directly in the process exiting flow, which will save swap-out
>     time
>     >>> and alleviate the load of the process exiting.
>     >>>
>     >>> Signed-off-by: Zhiguo Jiang <justinjiang@vivo.com>
>     >>> ---
>     >>>
>     >>> Change log:
>     >>> v4->v5:
>     >>> 1.Modify to skip non-shared anonymous folio only.
>     >>> 2.Update comments for pra->referenced = -1.
>     >>> v3->v4:
>     >>> 1.Modify that the unshared folios mapped only in exiting task
>     are skip.
>     >>> v2->v3:
>     >>> Nothing.
>     >>> v1->v2:
>     >>> 1.The VM_EXITING added in v1 patch is removed, because it will
>     fail
>     >>> to compile in 32-bit system.
>     >>>
>     >>>   mm/rmap.c   | 13 +++++++++++++
>     >>>   mm/vmscan.c |  7 ++++++-
>     >>>   2 files changed, 19 insertions(+), 1 deletion(-)
>     >>>
>     >>> diff --git a/mm/rmap.c b/mm/rmap.c
>     >>> index 26806b49a86f..5b5281d71dbb
>     >>> --- a/mm/rmap.c
>     >>> +++ b/mm/rmap.c
>     >>> @@ -843,6 +843,19 @@ static bool folio_referenced_one(struct
>     folio
>     >>> *folio,
>     >>>          int referenced = 0;
>     >>>          unsigned long start = address, ptes = 0;
>     >>>
>     >>> +       /*
>     >>> +        * Skip the non-shared anonymous folio mapped solely by
>     >>> +        * the single exiting process, and release it directly
>     >>> +        * in the process exiting.
>     >>> +        */
>     >>> +       if ((!atomic_read(&vma->vm_mm->mm_users) ||
>     >>> +               test_bit(MMF_OOM_SKIP, &vma->vm_mm->flags)) &&
>     >>> +               folio_test_anon(folio) &&
>     >>> folio_test_swapbacked(folio) &&
>     >>> + !folio_likely_mapped_shared(folio)) {
>     >>> +               pra->referenced = -1;
>     >>> +               return false;
>     >>> +       }
>     >>> +
>     >>>          while (page_vma_mapped_walk(&pvmw)) {
>     >>>                  address = pvmw.address;
>     > Sure, I agree with your modification suggestions. This way,
>     using PTL
>     > indeed sure
>     > that the folio is mapped by this process.
>     > Thanks
>     >> As David suggested, what about the below?
>     >>
>     >> @@ -883,6 +870,21 @@ static bool folio_referenced_one(struct folio
>     >> *folio,
>     >>                          continue;
>     >>                  }
>     >>
>     >> +               /*
>     >> +                * Skip the non-shared anonymous folio mapped
>     solely by
>     >> +                * the single exiting process, and release it
>     directly
>     >> +                * in the process exiting.
>     >> +                */
>     >> +               if ((!atomic_read(&vma->vm_mm->mm_users) ||
>     >> + test_bit(MMF_OOM_SKIP,
>     >> &vma->vm_mm->flags)) &&
>     >> + folio_test_anon(folio) &&
>     >> folio_test_swapbacked(folio) &&
>     >> + !folio_likely_mapped_shared(folio)) {
>     >> +                       pra->referenced = -1;
>     >> + page_vma_mapped_walk_done(&pvmw);
>     >> +                       return false;
>     >> +               }
>     >> +
>     >>                  if (pvmw.pte) {
>     >>                          if (lru_gen_enabled() &&
>     >> pte_young(ptep_get(pvmw.pte))) {
>     >>
>     >>
>     >> By the way, I am not convinced that using test_bit(MMF_OOM_SKIP,
>     >> &vma->vm_mm->flags) is
>     >> correct (I think it is wrong).   For example, global_init can
>     >> directly have it:
>     >>                  if (is_global_init(p)) {
>     >>                          can_oom_reap = false;
>     >>                          set_bit(MMF_OOM_SKIP, &mm->flags);
>     >>                          pr_info("oom killer %d (%s) has mm
>     pinned by
>     >> %d (%s)\n",
>     >> task_pid_nr(victim),
>     >> victim->comm,
>     >> task_pid_nr(p), p->comm);
>     >>                          continue;
>     >>                  }
>     >>
>     >> And exit_mmap() automatically has MMF_OOM_SKIP.
>     >>
>     >> What is the purpose of this check? Is there a better way to
>     determine
>     >> if a process is an
>     >> OOM target? What about check_stable_address_space() ?
>     > 1.Sorry, I overlook the situation with if (is_global_init(p)),
>     > MMF_OOM_SKIP is indeed not suitable.
>     >
>     > 2.check_stable_address_space() can indicate oom_reaper, but it
>     seems
>     > unable to identify the situation where the process exits normally.
>     > What about task_is_dying()? static inline bool
>     task_is_dying(void) {
>     > return tsk_is_oom_victim(current) ||
>     fatal_signal_pending(current) ||
>     > (current->flags & PF_EXITING); } Thanks
>     We can migrate task_is_dying() from mm/memcontrol.c to
>     include/linux/oom.h
>     > static inline bool task_is_dying(void)
>     > {
>     >     return tsk_is_oom_victim(current) ||
>     fatal_signal_pending(current) ||
>     >         (current->flags & PF_EXITING);
>     > }
>
>
> no. current is kswapd.
Hi Barry,

It seems feasible for check_stable_address_space() replacing MMF_OOM_SKIP.
check_stable_address_space() can indicate oom kill, and 
!atomic_read(&vma->vm_mm->mm_users)
can indicate the normal process exiting.

         /*
          * Skip the non-shared anonymous folio mapped solely by
          * the single exiting process, and release it directly
          * in the process exiting.
          */
         if ((!atomic_read(&vma->vm_mm->mm_users) ||
             check_stable_address_space(vma->vm_mm)) &&
             folio_test_anon(folio) && folio_test_swapbacked(folio) &&
             !folio_likely_mapped_shared(folio)) {
             pra->referenced = -1;
             page_vma_mapped_walk_done(&pvmw);
             return false;
         }

Thanks
Zhiguo
>
>
>     >>
>     >>
>     >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>     >>> index 0761f91b407f..bae7a8bf6b3d
>     >>> --- a/mm/vmscan.c
>     >>> +++ b/mm/vmscan.c
>     >>> @@ -863,7 +863,12 @@ static enum folio_references
>     >>> folio_check_references(struct folio *folio,
>     >>>          if (vm_flags & VM_LOCKED)
>     >>>                  return FOLIOREF_ACTIVATE;
>     >>>
>     >>> -       /* rmap lock contention: rotate */
>     >>> +       /*
>     >>> +        * There are two cases to consider.
>     >>> +        * 1) Rmap lock contention: rotate.
>     >>> +        * 2) Skip the non-shared anonymous folio mapped solely by
>     >>> +        *    the single exiting process.
>     >>> +        */
>     >>>          if (referenced_ptes == -1)
>     >>>                  return FOLIOREF_KEEP;
>     >>>
>     >>> --
>     >>> 2.39.0
>     >>>
>     >> Thanks
>     >> Barry
>     >
>