[PATCH 1/2] mm, memcontrol: Move swap charge handling into get_swap_page()

[Tejun Heo]

get_swap_page() is always followed by mem_cgroup_try_charge_swap().
This patch moves mem_cgroup_try_charge_swap() into get_swap_page() and
makes get_swap_page() call the function even after swap allocation
failure.

This simplifies the callers and consolidates memcg related logic and
will ease adding swap related memcg events.

Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Michal Hocko <mho...@kernel.org>
Cc: Vladimir Davydov <vdavydov....@gmail.com>
Cc: Roman Gushchin <g...@fb.com>
Cc: Rik van Riel <r...@surriel.com>
Cc: Andrew Morton <a...@linux-foundation.org>
---
 mm/memcontrol.c |  3 +++
 mm/shmem.c      |  4 ----
 mm/swap_slots.c | 10 +++++++---
 mm/swap_state.c |  3 ---
 4 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d5bf01d..9f9c8a7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5987,6 +5987,9 @@ int mem_cgroup_try_charge_swap(struct page *page, 
swp_entry_t entry)
        if (!memcg)
                return 0;
 
+       if (!entry.val)
+               return 0;
+
        memcg = mem_cgroup_id_get_online(memcg);
 
        if (!mem_cgroup_is_root(memcg) &&
diff --git a/mm/shmem.c b/mm/shmem.c
index 1907688..4a07d21 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1313,9 +1313,6 @@ static int shmem_writepage(struct page *page, struct 
writeback_control *wbc)
        if (!swap.val)
                goto redirty;
 
-       if (mem_cgroup_try_charge_swap(page, swap))
-               goto free_swap;
-
        /*
         * Add inode to shmem_unuse()'s list of swapped-out inodes,
         * if it's not already there.  Do it now before the page is
@@ -1344,7 +1341,6 @@ static int shmem_writepage(struct page *page, struct 
writeback_control *wbc)
        }
 
        mutex_unlock(&shmem_swaplist_mutex);
-free_swap:
        put_swap_page(page, swap);
 redirty:
        set_page_dirty(page);
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index bebc192..7546eb2 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -319,7 +319,7 @@ swp_entry_t get_swap_page(struct page *page)
        if (PageTransHuge(page)) {
                if (IS_ENABLED(CONFIG_THP_SWAP))
                        get_swap_pages(1, true, &entry);
-               return entry;
+               goto out;
        }
 
        /*
@@ -349,11 +349,15 @@ swp_entry_t get_swap_page(struct page *page)
                }
                mutex_unlock(&cache->alloc_lock);
                if (entry.val)
-                       return entry;
+                       goto out;
        }
 
        get_swap_pages(1, false, &entry);
-
+out:
+       if (mem_cgroup_try_charge_swap(page, entry)) {
+               put_swap_page(page, entry);
+               entry.val = 0;
+       }
        return entry;
 }
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 39ae7cf..41f0809 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -216,9 +216,6 @@ int add_to_swap(struct page *page)
        if (!entry.val)
                return 0;
 
-       if (mem_cgroup_try_charge_swap(page, entry))
-               goto fail;
-
        /*
         * Radix-tree node allocations from PF_MEMALLOC contexts could
         * completely exhaust the page allocator. __GFP_NOMEMALLOC
-- 
2.9.5