path: root/mm/swap_state.c
diff options
authorVladimir Davydov <vdavydov@virtuozzo.com>2016-01-20 15:02:56 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-20 17:09:18 -0800
commit37e84351198be087335ad2b2253b35c7cc76a5ad (patch)
tree3f7cfe687fdc86bea76f2e47787ff1f7c79bef23 /mm/swap_state.c
parentmm: memcontrol: clean up alloc, online, offline, free functions (diff)
mm: memcontrol: charge swap to cgroup2
This patchset introduces swap accounting to cgroup2. This patch (of 7): In the legacy hierarchy we charge memsw, which is dubious, because: - memsw.limit must be >= memory.limit, so it is impossible to limit swap usage less than memory usage. Taking into account the fact that the primary limiting mechanism in the unified hierarchy is memory.high while memory.limit is either left unset or set to a very large value, moving memsw.limit knob to the unified hierarchy would effectively make it impossible to limit swap usage according to the user preference. - memsw.usage != memory.usage + swap.usage, because a page occupying both swap entry and a swap cache page is charged only once to memsw counter. As a result, it is possible to effectively eat up to memory.limit of memory pages *and* memsw.limit of swap entries, which looks unexpected. That said, we should provide a different swap limiting mechanism for cgroup2. This patch adds mem_cgroup->swap counter, which charges the actual number of swap entries used by a cgroup. It is only charged in the unified hierarchy, while the legacy hierarchy memsw logic is left intact. The swap usage can be monitored using new memory.swap.current file and limited using memory.swap.max. Note, to charge swap resource properly in the unified hierarchy, we have to make swap_entry_free uncharge swap only when ->usage reaches zero, not just ->count, i.e. when all references to a swap entry, including the one taken by swap cache, are gone. This is necessary, because otherwise swap-in could result in uncharging swap even if the page is still in swap cache and hence still occupies a swap entry. At the same time, this shouldn't break memsw counter logic, where a page is never charged twice for using both memory and swap, because in case of legacy hierarchy we uncharge swap on commit (see mem_cgroup_commit_charge). Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
1 files changed, 5 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 676ff2991380..69cb2464e7dc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -170,6 +170,11 @@ int add_to_swap(struct page *page, struct list_head *list)
if (!entry.val)
return 0;
+ if (mem_cgroup_try_charge_swap(page, entry)) {
+ swapcache_free(entry);
+ return 0;
+ }
if (unlikely(PageTransHuge(page)))
if (unlikely(split_huge_page_to_list(page, list))) {