mm/swap: add cache for swap slots allocation

We add per cpu caches for swap slots that can be allocated and freed
quickly without the need to touch the swap info lock.

Two separate caches are maintained for swap slots allocated and swap
slots returned.  This is to allow the swap slots to be returned to the
global pool in a batch so they will have a chance to be coaelesced with
other slots in a cluster.  We do not reuse the slots that are returned
right away, as it may increase fragmentation of the slots.

The swap allocation cache is protected by a mutex as we may sleep when
searching for empty slots in cache.  The swap free cache is protected by
a spin lock as we cannot sleep in the free path.

We refill the swap slots cache when we run out of slots, and we disable
the swap slots cache and drain the slots if the global number of slots
fall below a low watermark threshold.  We re-enable the cache agian when
the slots available are above a high watermark.

[ying.huang@intel.com: use raw_cpu_ptr over this_cpu_ptr for swap slots access]
[tim.c.chen@linux.intel.com: add comments on locks in swap_slots.h]
  Link: http://lkml.kernel.org/r/20170118180327.GA24225@linux.intel.com
Link: http://lkml.kernel.org/r/35de301a4eaa8daa2977de6e987f2c154385eb66.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h
new file mode 100644
index 000000000000..ba5623b27c60
--- /dev/null
+++ b/include/linux/swap_slots.h
@@ -0,0 +1,28 @@
+#ifndef _LINUX_SWAP_SLOTS_H
+#define _LINUX_SWAP_SLOTS_H
+
+#include <linux/swap.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+
+#define SWAP_SLOTS_CACHE_SIZE			SWAP_BATCH
+#define THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE	(5*SWAP_SLOTS_CACHE_SIZE)
+#define THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE	(2*SWAP_SLOTS_CACHE_SIZE)
+
+struct swap_slots_cache {
+	bool		lock_initialized;
+	struct mutex	alloc_lock; /* protects slots, nr, cur */
+	swp_entry_t	*slots;
+	int		nr;
+	int		cur;
+	spinlock_t	free_lock;  /* protects slots_ret, n_ret */
+	swp_entry_t	*slots_ret;
+	int		n_ret;
+};
+
+void disable_swap_slots_cache_lock(void);
+void reenable_swap_slots_cache_unlock(void);
+int enable_swap_slots_cache(void);
+int free_swap_slot(swp_entry_t entry);
+
+#endif /* _LINUX_SWAP_SLOTS_H */