Re: [PATCH 1/2] mm/rmap: support folio_referenced to control if try_lock in rmap_walk

[Barry Song]

Hi peifeng,

On Tue, Feb 20, 2024 at 2:43 PM 李培锋 <lipeifeng@xxxxxxxx> wrote:
>
> add more experts from Linux and Google.
>
>
> 在 2024/2/19 22:17, lipeifeng@xxxxxxxx 写道:
> > From: lipeifeng <lipeifeng@xxxxxxxx>
> >
> > The patch to support folio_referenced to control the bevavior
> > of walk_rmap, which for some thread to hold the lock in rmap_walk
> > instead of try_lock when using folio_referenced.

please describe what problem the patch is trying to address,
and why this modification is needed in commit message.

btw, who is set rw_try_lock to 0, what is the benefit?

> >
> > Signed-off-by: lipeifeng <lipeifeng@xxxxxxxx>
> > ---
> >   include/linux/rmap.h |  5 +++--
> >   mm/rmap.c            |  5 +++--
> >   mm/vmscan.c          | 16 ++++++++++++++--
> >   3 files changed, 20 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > index b7944a8..846b261 100644
> > --- a/include/linux/rmap.h
> > +++ b/include/linux/rmap.h
> > @@ -623,7 +623,8 @@ static inline int folio_try_share_anon_rmap_pmd(struct folio *folio,
> >    * Called from mm/vmscan.c to handle paging out
> >    */
> >   int folio_referenced(struct folio *, int is_locked,
> > -                     struct mem_cgroup *memcg, unsigned long *vm_flags);
> > +                     struct mem_cgroup *memcg, unsigned long *vm_flags,
> > +                     unsigned int rw_try_lock);
> >
> >   void try_to_migrate(struct folio *folio, enum ttu_flags flags);
> >   void try_to_unmap(struct folio *, enum ttu_flags flags);
> > @@ -739,7 +740,7 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
> >
> >   static inline int folio_referenced(struct folio *folio, int is_locked,
> >                                 struct mem_cgroup *memcg,
> > -                               unsigned long *vm_flags)
> > +                               unsigned long *vm_flags, unsigned int rw_try_lock)
> >   {
> >       *vm_flags = 0;
> >       return 0;
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index f5d43ed..15d1fba 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -952,6 +952,7 @@ static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
> >    * @is_locked: Caller holds lock on the folio.
> >    * @memcg: target memory cgroup
> >    * @vm_flags: A combination of all the vma->vm_flags which referenced the folio.
> > + * @rw_try_lock: if try_lock in rmap_walk
> >    *
> >    * Quick test_and_clear_referenced for all mappings of a folio,
> >    *
> > @@ -959,7 +960,7 @@ static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
> >    * the function bailed out due to rmap lock contention.
> >    */
> >   int folio_referenced(struct folio *folio, int is_locked,
> > -                  struct mem_cgroup *memcg, unsigned long *vm_flags)
> > +                  struct mem_cgroup *memcg, unsigned long *vm_flags, unsigned int rw_try_lock)
> >   {
> >       int we_locked = 0;
> >       struct folio_referenced_arg pra = {
> > @@ -970,7 +971,7 @@ int folio_referenced(struct folio *folio, int is_locked,
> >               .rmap_one = folio_referenced_one,
> >               .arg = (void *)&pra,
> >               .anon_lock = folio_lock_anon_vma_read,
> > -             .try_lock = true,
> > +             .try_lock = rw_try_lock ? true : false,
> >               .invalid_vma = invalid_folio_referenced_vma,
> >       };
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 4f9c854..0296d48 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -136,6 +136,9 @@ struct scan_control {
> >       /* Always discard instead of demoting to lower tier memory */
> >       unsigned int no_demotion:1;
> >
> > +     /* if try_lock in rmap_walk */
> > +     unsigned int rw_try_lock:1;
> > +
> >       /* Allocation order */
> >       s8 order;
> >
> > @@ -827,7 +830,7 @@ static enum folio_references folio_check_references(struct folio *folio,
> >       unsigned long vm_flags;
> >
> >       referenced_ptes = folio_referenced(folio, 1, sc->target_mem_cgroup,
> > -                                        &vm_flags);
> > +                                        &vm_flags, sc->rw_try_lock);
> >       referenced_folio = folio_test_clear_referenced(folio);
> >
> >       /*
> > @@ -1501,6 +1504,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> >       struct scan_control sc = {
> >               .gfp_mask = GFP_KERNEL,
> >               .may_unmap = 1,
> > +             .rw_try_lock = 1,
> >       };
> >       struct reclaim_stat stat;
> >       unsigned int nr_reclaimed;
> > @@ -2038,7 +2042,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
> >
> >               /* Referenced or rmap lock contention: rotate */
> >               if (folio_referenced(folio, 0, sc->target_mem_cgroup,
> > -                                  &vm_flags) != 0) {
> > +                                  &vm_flags, sc->rw_try_lock) != 0) {
> >                       /*
> >                        * Identify referenced, file-backed active folios and
> >                        * give them one more trip around the active list So
> > @@ -2096,6 +2100,7 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list,
> >               .may_unmap = 1,
> >               .may_swap = 1,
> >               .no_demotion = 1,
> > +             .rw_try_lock = 1,
> >       };
> >
> >       nr_reclaimed = shrink_folio_list(folio_list, pgdat, &sc, &dummy_stat, false);
> > @@ -5442,6 +5447,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
> >               .may_swap = true,
> >               .reclaim_idx = MAX_NR_ZONES - 1,
> >               .gfp_mask = GFP_KERNEL,
> > +             .rw_try_lock = 1,
> >       };
> >
> >       buf = kvmalloc(len + 1, GFP_KERNEL);
> > @@ -6414,6 +6420,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> >               .may_writepage = !laptop_mode,
> >               .may_unmap = 1,
> >               .may_swap = 1,
> > +             .rw_try_lock = 1,
> >       };
> >
> >       /*
> > @@ -6459,6 +6466,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
> >               .may_unmap = 1,
> >               .reclaim_idx = MAX_NR_ZONES - 1,
> >               .may_swap = !noswap,
> > +             .rw_try_lock = 1,
> >       };
> >
> >       WARN_ON_ONCE(!current->reclaim_state);
> > @@ -6503,6 +6511,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> >               .may_unmap = 1,
> >               .may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP),
> >               .proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE),
> > +             .rw_try_lock = 1,
> >       };
> >       /*
> >        * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
> > @@ -6764,6 +6773,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
> >               .gfp_mask = GFP_KERNEL,
> >               .order = order,
> >               .may_unmap = 1,
> > +             .rw_try_lock = 1,
> >       };
> >
> >       set_task_reclaim_state(current, &sc.reclaim_state);
> > @@ -7223,6 +7233,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> >               .may_unmap = 1,
> >               .may_swap = 1,
> >               .hibernation_mode = 1,
> > +             .rw_try_lock = 1,
> >       };
> >       struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
> >       unsigned long nr_reclaimed;
> > @@ -7381,6 +7392,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> >               .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
> >               .may_swap = 1,
> >               .reclaim_idx = gfp_zone(gfp_mask),
> > +             .rw_try_lock = 1,
> >       };
> >       unsigned long pflags;
> >
Thanks
Barry