Re: [PATCH v6 2/6] memcontrol: allows mem_cgroup_iter() to check for onlineness

[Nhat Pham <nphamcs@gmail.com>]

On Mon, Nov 27, 2023 at 1:43 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 27 Nov 2023 11:36:59 -0800 Nhat Pham <nphamcs@gmail.com> wrote:
>
> > The new zswap writeback scheme requires an online-only memcg hierarchy
> > traversal. Add a new parameter to mem_cgroup_iter() to check for
> > onlineness before returning.
>
> I get a few build errors, perhaps because of patch timing issues...

Ah I thought I got all of them. Must have somehow missed it.

>
> mm/shrinker_debug.c: In function 'shrinker_debugfs_count_show':
> mm/shrinker_debug.c:64:17: error: too few arguments to function 'mem_cgroup_iter'
>    64 |         memcg = mem_cgroup_iter(NULL, NULL, NULL);
>       |                 ^~~~~~~~~~~~~~~
> In file included from mm/shrinker_debug.c:7:
> ./include/linux/memcontrol.h:833:20: note: declared here
>   833 | struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
>       |                    ^~~~~~~~~~~~~~~
> mm/shrinker_debug.c:89:27: error: too few arguments to function 'mem_cgroup_iter'
>    89 |         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
>       |                           ^~~~~~~~~~~~~~~
> ./include/linux/memcontrol.h:833:20: note: declared here
>   833 | struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
>       |                    ^~~~~~~~~~~~~~~
> mm/damon/sysfs-schemes.c: In function 'damon_sysfs_memcg_path_to_id':
> mm/damon/sysfs-schemes.c:1594:22: error: too few arguments to function 'mem_cgroup_iter'
>  1594 |         for (memcg = mem_cgroup_iter(NULL, NULL, NULL); memcg;
>       |                      ^~~~~~~~~~~~~~~
> In file included from ./include/linux/damon.h:11,
>                  from mm/damon/sysfs-common.h:8,
>                  from mm/damon/sysfs-schemes.c:10:
> ./include/linux/memcontrol.h:833:20: note: declared here
>   833 | struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
>       |                    ^~~~~~~~~~~~~~~
> mm/damon/sysfs-schemes.c:1595:33: error: too few arguments to function 'mem_cgroup_iter'
>  1595 |                         memcg = mem_cgroup_iter(NULL, memcg, NULL)) {
>       |                                 ^~~~~~~~~~~~~~~
> ./include/linux/memcontrol.h:833:20: note: declared here
>   833 | struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
>       |                    ^~~~~~~~~~~~~~~
>
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -832,7 +832,7 @@ static inline void mem_cgroup_put(struct mem_cgroup *memcg)
> >
> >  struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
> >                                  struct mem_cgroup *,
> > -                                struct mem_cgroup_reclaim_cookie *);
> > +                                struct mem_cgroup_reclaim_cookie *, bool online);
>
> How many callsites do we expect to utilize the new `online' argument?
> Few, I suspect.
>
> How about we fix the above and simplify the patch by adding a new
> mem_cgroup_iter_online() and make mem_cgroup_iter() a one-line wrapper
> which calls that and adds the online=false argument?

But yes, this is a much smarter idea. Should have thought about it initially :)

>
> I also saw this, didn't investigate.
>
> drivers/android/binder_alloc.c: In function 'binder_update_page_range':
> drivers/android/binder_alloc.c:237:34: error: too few arguments to function 'list_lru_del'
>   237 |                         on_lru = list_lru_del(&binder_alloc_lru, &page->lru);

Oh yeah I missed this too - it's due to the API change introduced to
the previous bug. The old "list_lru_del" is now "list_lru_del_obj".

Let me double check everything again and send out the fixes. My apologies.

>