Subject: Re: mmotm 2021-01-12-01-57 uploaded (NR_SWAPCACHE in mm/)

From: Andrew Morton <[email-masked]>
Date: Tue, 12 Jan 2021 13:50:10 -0800

On Tue, 12 Jan 2021 12:38:18 -0800 Randy Dunlap <[email-masked]> wrote:

> On 1/12/21 1:58 AM, [email-masked] wrote:
> > The mm-of-the-moment snapshot 2021-01-12-01-57 has been uploaded to
> > 
> >    https://www.ozlabs.org/~akpm/mmotm/
> > 
> > mmotm-readme.txt says
> > 
> > README for mm-of-the-moment:
> > 
> > https://www.ozlabs.org/~akpm/mmotm/
> > 
> > This is a snapshot of my -mm patch queue.  Uploaded at random hopefully
> > more than once a week.
> > 
> 
> on i386 and x86_64:
> 
> when CONFIG_SWAP is not set/enabled:
> 
> ../mm/migrate.c: In function ‘migrate_page_move_mapping’:
> ../mm/migrate.c:504:35: error: ‘NR_SWAPCACHE’ undeclared (first use in this function); did you mean ‘QC_SPACE’?
>     __mod_lruvec_state(old_lruvec, NR_SWAPCACHE, -nr);
>                                    ^~~~~~~~~~~~
> 
> ../mm/memcontrol.c:1529:20: error: ‘NR_SWAPCACHE’ undeclared here (not in a function); did you mean ‘SGP_CACHE’?
>   { "swapcached",   NR_SWAPCACHE   },
>                     ^~~~~~~~~~~~

Thanks.  I did the below.

But we're still emitting "Node %d SwapCached: 0 kB" in sysfs when
CONFIG_SWAP=n, which is probably wrong.  Shakeel, can you please have a
think?

--- a/mm/memcontrol.c~mm-memcg-add-swapcache-stat-for-memcg-v2-fix
+++ a/mm/memcontrol.c
@@ -1521,7 +1521,9 @@ static const struct memory_stat memory_s
 	{ "file_mapped",		NR_FILE_MAPPED			},
 	{ "file_dirty",			NR_FILE_DIRTY			},
 	{ "file_writeback",		NR_WRITEBACK			},
+#ifdef CONFIG_SWAP
 	{ "swapcached",			NR_SWAPCACHE			},
+#endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	{ "anon_thp",			NR_ANON_THPS			},
 	{ "file_thp",			NR_FILE_THPS			},
--- a/mm/migrate.c~mm-memcg-add-swapcache-stat-for-memcg-v2-fix
+++ a/mm/migrate.c
@@ -500,10 +500,12 @@ int migrate_page_move_mapping(struct add
 			__mod_lruvec_state(old_lruvec, NR_SHMEM, -nr);
 			__mod_lruvec_state(new_lruvec, NR_SHMEM, nr);
 		}
+#ifdef CONFIG_SWAP
 		if (PageSwapCache(page)) {
 			__mod_lruvec_state(old_lruvec, NR_SWAPCACHE, -nr);
 			__mod_lruvec_state(new_lruvec, NR_SWAPCACHE, nr);
 		}
+#endif
 		if (dirty && mapping_can_writeback(mapping)) {
 			__mod_lruvec_state(old_lruvec, NR_FILE_DIRTY, -nr);
 			__mod_zone_page_state(oldzone, NR_ZONE_WRITE_PENDING, -nr);
_