mm, shmem: add internal shmem resident memory accounting

Currently looking at /proc/<pid>/status or statm, there is no way to
distinguish shmem pages from pages mapped to a regular file (shmem pages
are mapped to /dev/zero), even though their implication in actual memory
use is quite different.

The internal accounting currently counts shmem pages together with
regular files.  As a preparation to extend the userspace interfaces,
this patch adds MM_SHMEMPAGES counter to mm_rss_stat to account for
shmem pages separately from MM_FILEPAGES.  The next patch will expose it
to userspace - this patch doesn't change the exported values yet, by
adding up MM_SHMEMPAGES to MM_FILEPAGES at places where MM_FILEPAGES was
used before.  The only user-visible change after this patch is the OOM
killer message that separates the reported "shmem-rss" from "file-rss".

[vbabka@suse.cz: forward-porting, tweak changelog]
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 9 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 3c3f1d21f075..622756c16ac8 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1364,10 +1364,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                 if (PageHuge(page)) {
                         hugetlb_count_sub(1 << compound_order(page), mm);
                 } else {
-                        if (PageAnon(page))
-                                dec_mm_counter(mm, MM_ANONPAGES);
-                        else
-                                dec_mm_counter(mm, MM_FILEPAGES);
+                        dec_mm_counter(mm, mm_counter(page));
                 }
                 set_pte_at(mm, address, pte,
                            swp_entry_to_pte(make_hwpoison_entry(page)));
@@ -1377,10 +1374,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                  * interest anymore. Simply discard the pte, vmscan
                  * will take care of the rest.
                  */
-                if (PageAnon(page))
-                        dec_mm_counter(mm, MM_ANONPAGES);
-                else
-                        dec_mm_counter(mm, MM_FILEPAGES);
+                dec_mm_counter(mm, mm_counter(page));
         } else if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION)) {
                 swp_entry_t entry;
                 pte_t swp_pte;
@@ -1420,7 +1414,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                         swp_pte = pte_swp_mksoft_dirty(swp_pte);
                 set_pte_at(mm, address, pte, swp_pte);
         } else
-                dec_mm_counter(mm, MM_FILEPAGES);
+                dec_mm_counter(mm, mm_counter_file(page));
 
         page_remove_rmap(page);
         page_cache_release(page);