This patch makes __remove_mapping() not remove a page from
pagecache on memcg reclaim. After all mappings are removed
and refcounter is freezed, we uncharge page memcg. Further
putback_lru_page() places page into root_mem_cgroup, so it
remains in pagecache till global reclaim. This gives memcg
tasks extra possibility to obtain page from pagecache
instead of launching IO.
Next patch makes pagecache_get_page() to recharge a page
in case of its memcg is NULL (i.e., on first access after
uncharging). It looks to be the only function, which is
used by filesystems to obtain a pagecache page. Here we
introduce AS_KEEP_MEMCG_RECLAIM flag to mark the filesystems,
which are reviewed, that they really follow this way. It
has a sense to keep pages in __remove_mapping() only for
them. Later, we remove this flags after all filesystems are
reviewed.
Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
include/linux/pagemap.h | 1 +
mm/vmscan.c | 22 ++++++++++++++++++----
2 files changed, 19 insertions(+), 4 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 1020e6f40880..1b880da85868 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -29,6 +29,7 @@ enum mapping_flags {
AS_EXITING = 4, /* final truncate in progress */
/* writeback related tags are not used */
AS_NO_WRITEBACK_TAGS = 5,
+ AS_KEEP_MEMCG_RECLAIM = 6,
};
/**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a714c4f800e9..7237603c8973 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -887,7 +887,7 @@ static pageout_t pageout(struct page *page, struct
address_space *mapping,
* gets returned with a refcount of 0.
*/
static int __remove_mapping(struct address_space *mapping, struct page *page,
- bool reclaimed)
+ bool reclaimed, bool memcg_reclaim)
{
unsigned long flags;
int refcount;
@@ -963,7 +963,20 @@ static int __remove_mapping(struct address_space *mapping,
struct page *page,
if (reclaimed && page_is_file_cache(page) &&
!mapping_exiting(mapping) && !dax_mapping(mapping))
shadow = workingset_eviction(mapping, page);
- __delete_from_page_cache(page, shadow);
+#ifdef CONFIG_MEMCG
+ if (memcg_reclaim &&
+ test_bit(AS_KEEP_MEMCG_RECLAIM, &mapping->flags)) {
+ /*
+ * Page is not dirty/writeback/mapped, so we may avoid
+ * taking mem_cgroup::move_lock for changing its memcg.
+ * See mem_cgroup_move_account() for details.
+ */
+ mem_cgroup_uncharge(page);
+ page_ref_unfreeze(page, refcount);
+ goto cannot_free;
+ } else
+#endif
+ __delete_from_page_cache(page, shadow);
xa_unlock_irqrestore(&mapping->i_pages, flags);
if (freepage != NULL)
@@ -985,7 +998,7 @@ static int __remove_mapping(struct address_space *mapping,
struct page *page,
*/
int remove_mapping(struct address_space *mapping, struct page *page)
{
- if (__remove_mapping(mapping, page, false)) {
+ if (__remove_mapping(mapping, page, false, false)) {
/*
* Unfreezing the refcount with 1 rather than 2 effectively
* drops the pagecache ref for us without requiring another
@@ -1458,7 +1471,8 @@ static unsigned long shrink_page_list(struct list_head
*page_list,
count_vm_event(PGLAZYFREED);
count_memcg_page_event(page, PGLAZYFREED);
- } else if (!mapping || !__remove_mapping(mapping, page, true))
+ } else if (!mapping || !__remove_mapping(mapping, page, true,
+ !global_reclaim(sc)))
goto keep_locked;
unlock_page(page);
