mm: remove swap token code

The swap token code no longer fits in with the current VM model.  It
does not play well with cgroups or the better NUMA placement code in
development, since we have only one swap token globally.

It also has the potential to mess with scalability of the system, by
increasing the number of non-reclaimable pages on the active and
inactive anon LRU lists.

Last but not least, the swap token code has been broken for a year
without complaints, as reported by Konstantin Khlebnikov.  This suggests
we no longer have much use for it.

The days of sub-1G memory systems with heavy use of swap are over.  If
we ever need thrashing reducing code in the future, we will have to
implement something that does scale.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Bob Picco <bpicco@meloft.net>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 2 insertions, 170 deletions

diff --git a/mm/Makefile b/mm/Makefile
index 8aada89efbb..ccecbf9818f 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -25,7 +25,7 @@ endif
 obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
 
 obj-$(CONFIG_BOUNCE)	+= bounce.o
-obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o thrash.o
+obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
 obj-$(CONFIG_NUMA) 	+= mempolicy.o
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f342778a0c0..92675fe8a2e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5598,7 +5598,6 @@ static void mem_cgroup_move_task(struct cgroup *cont,
 	if (mm) {
 		if (mc.to)
 			mem_cgroup_move_charge(mm);
-		put_swap_token(mm);
 		mmput(mm);
 	}
 	if (mc.to)
diff --git a/mm/memory.c b/mm/memory.c
index e40f6759ba9..2bf9e110437 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2908,7 +2908,6 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
 	page = lookup_swap_cache(entry);
 	if (!page) {
-		grab_swap_token(mm); /* Contend for token _before_ read-in */
 		page = swapin_readahead(entry,
 					GFP_HIGHUSER_MOVABLE, vma, address);
 		if (!page) {
@@ -2938,6 +2937,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 
 	locked = lock_page_or_retry(page, mm, flags);
+
 	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 	if (!locked) {
 		ret |= VM_FAULT_RETRY;
diff --git a/mm/rmap.c b/mm/rmap.c
index 5b5ad584ffb..0f3b7cda2a2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -755,12 +755,6 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 		pte_unmap_unlock(pte, ptl);
 	}
 
-	/* Pretend the page is referenced if the task has the
-	   swap token and is in the middle of a page fault. */
-	if (mm != current->mm && has_swap_token(mm) &&
-			rwsem_is_locked(&mm->mmap_sem))
-		referenced++;
-
 	(*mapcount)--;
 
 	if (referenced)
diff --git a/mm/thrash.c b/mm/thrash.c
deleted file mode 100644
index 57ad495dbd5..00000000000
--- a/mm/thrash.c
+++ /dev/null
@@ -1,155 +0,0 @@
-/*
- * mm/thrash.c
- *
- * Copyright (C) 2004, Red Hat, Inc.
- * Copyright (C) 2004, Rik van Riel <riel@redhat.com>
- * Released under the GPL, see the file COPYING for details.
- *
- * Simple token based thrashing protection, using the algorithm
- * described in: http://www.cse.ohio-state.edu/hpcs/WWW/HTML/publications/abs05-1.html
- *
- * Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
- * Improved algorithm to pass token:
- * Each task has a priority which is incremented if it contended
- * for the token in an interval less than its previous attempt.
- * If the token is acquired, that task's priority is boosted to prevent
- * the token from bouncing around too often and to let the task make
- * some progress in its execution.
- */
-
-#include <linux/jiffies.h>
-#include <linux/mm.h>
-#include <linux/sched.h>
-#include <linux/swap.h>
-#include <linux/memcontrol.h>
-
-#include <trace/events/vmscan.h>
-
-#define TOKEN_AGING_INTERVAL	(0xFF)
-
-static DEFINE_SPINLOCK(swap_token_lock);
-struct mm_struct *swap_token_mm;
-static struct mem_cgroup *swap_token_memcg;
-
-#ifdef CONFIG_CGROUP_MEM_RES_CTLR
-static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
-{
-	struct mem_cgroup *memcg;
-
-	memcg = try_get_mem_cgroup_from_mm(mm);
-	if (memcg)
-		css_put(mem_cgroup_css(memcg));
-
-	return memcg;
-}
-#else
-static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
-{
-	return NULL;
-}
-#endif
-
-void grab_swap_token(struct mm_struct *mm)
-{
-	int current_interval;
-	unsigned int old_prio = mm->token_priority;
-	static unsigned int global_faults;
-	static unsigned int last_aging;
-
-	global_faults++;
-
-	current_interval = global_faults - mm->faultstamp;
-
-	if (!spin_trylock(&swap_token_lock))
-		return;
-
-	/* First come first served */
-	if (!swap_token_mm)
-		goto replace_token;
-
-	/*
-	 * Usually, we don't need priority aging because long interval faults
-	 * makes priority decrease quickly. But there is one exception. If the
-	 * token owner task is sleeping, it never make long interval faults.
-	 * Thus, we need a priority aging mechanism instead. The requirements
-	 * of priority aging are
-	 *  1) An aging interval is reasonable enough long. Too short aging
-	 *     interval makes quick swap token lost and decrease performance.
-	 *  2) The swap token owner task have to get priority aging even if
-	 *     it's under sleep.
-	 */
-	if ((global_faults - last_aging) > TOKEN_AGING_INTERVAL) {
-		swap_token_mm->token_priority /= 2;
-		last_aging = global_faults;
-	}
-
-	if (mm == swap_token_mm) {
-		mm->token_priority += 2;
-		goto update_priority;
-	}
-
-	if (current_interval < mm->last_interval)
-		mm->token_priority++;
-	else {
-		if (likely(mm->token_priority > 0))
-			mm->token_priority--;
-	}
-
-	/* Check if we deserve the token */
-	if (mm->token_priority > swap_token_mm->token_priority)
-		goto replace_token;
-
-update_priority:
-	trace_update_swap_token_priority(mm, old_prio, swap_token_mm);
-
-out:
-	mm->faultstamp = global_faults;
-	mm->last_interval = current_interval;
-	spin_unlock(&swap_token_lock);
-	return;
-
-replace_token:
-	mm->token_priority += 2;
-	trace_replace_swap_token(swap_token_mm, mm);
-	swap_token_mm = mm;
-	swap_token_memcg = swap_token_memcg_from_mm(mm);
-	last_aging = global_faults;
-	goto out;
-}
-
-/* Called on process exit. */
-void __put_swap_token(struct mm_struct *mm)
-{
-	spin_lock(&swap_token_lock);
-	if (likely(mm == swap_token_mm)) {
-		trace_put_swap_token(swap_token_mm);
-		swap_token_mm = NULL;
-		swap_token_memcg = NULL;
-	}
-	spin_unlock(&swap_token_lock);
-}
-
-static bool match_memcg(struct mem_cgroup *a, struct mem_cgroup *b)
-{
-	if (!a)
-		return true;
-	if (!b)
-		return true;
-	if (a == b)
-		return true;
-	return false;
-}
-
-void disable_swap_token(struct mem_cgroup *memcg)
-{
-	/* memcg reclaim don't disable unrelated mm token. */
-	if (match_memcg(memcg, swap_token_memcg)) {
-		spin_lock(&swap_token_lock);
-		if (match_memcg(memcg, swap_token_memcg)) {
-			trace_disable_swap_token(swap_token_mm);
-			swap_token_mm = NULL;
-			swap_token_memcg = NULL;
-		}
-		spin_unlock(&swap_token_lock);
-	}
-}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 33dc256033b..ca46080bb07 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2352,8 +2352,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 
 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
 		sc->nr_scanned = 0;
-		if (!priority)
-			disable_swap_token(sc->target_mem_cgroup);
 		aborted_reclaim = shrink_zones(priority, zonelist, sc);
 
 		/*
@@ -2704,10 +2702,6 @@ loop_again:
 		unsigned long lru_pages = 0;
 		int has_under_min_watermark_zone = 0;
 
-		/* The swap token gets in the way of swapout... */
-		if (!priority)
-			disable_swap_token(NULL);
-
 		all_zones_ok = 1;
 		balanced = 0;