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Subject[PATCH 1/2] mm, memcontrol: Move swap charge handling into get_swap_page()
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 <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@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(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6012,6 +6012,9 @@ int mem_cgroup_try_charge_swap(struct pa
if (!memcg)
return 0;

+ if (!entry.val)
+ return 0;
+
memcg = mem_cgroup_id_get_online(memcg);

if (!mem_cgroup_is_root(memcg) &&
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1322,9 +1322,6 @@ static int shmem_writepage(struct page *
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
@@ -1353,7 +1350,6 @@ static int shmem_writepage(struct page *
}

mutex_unlock(&shmem_swaplist_mutex);
-free_swap:
put_swap_page(page, swap);
redirty:
set_page_dirty(page);
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -317,7 +317,7 @@ swp_entry_t get_swap_page(struct page *p
if (PageTransHuge(page)) {
if (IS_ENABLED(CONFIG_THP_SWAP))
get_swap_pages(1, true, &entry);
- return entry;
+ goto out;
}

/*
@@ -347,10 +347,14 @@ repeat:
}
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;
}
--- 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
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