linux-kernel - [PATCH -v2 02/10] mm, memcg: Add swap_cgroup

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Date:   Thu,  1 Sep 2016 08:16:55 -0700
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     tim.c.chen@...el.com, dave.hansen@...el.com, andi.kleen@...el.com,
        aaron.lu@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
        cgroups@...r.kernel.org
Subject: [PATCH -v2 02/10] mm, memcg: Add swap_cgroup_iter iterator

From: Huang Ying <ying.huang@...el.com>

The swap cgroup uses a kind of discontinuous array to record the
information for the swap entries.  lookup_swap_cgroup() provides a good
encapsulation to access one element of the discontinuous array.  To make
it easier to access multiple elements of the discontinuous array, an
iterator for the swap cgroup named swap_cgroup_iter is added in this
patch.

This will be used for transparent huge page (THP) swap support.  Where
the swap_cgroup for multiple swap entries will be changed together.

Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Vladimir Davydov <vdavydov@...tuozzo.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: cgroups@...r.kernel.org
Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
---
 mm/swap_cgroup.c | 62 +++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index 310ac0b..3563b8b 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -18,6 +18,13 @@ struct swap_cgroup {
 };
 #define SC_PER_PAGE	(PAGE_SIZE/sizeof(struct swap_cgroup))
 
+struct swap_cgroup_iter {
+	struct swap_cgroup_ctrl *ctrl;
+	struct swap_cgroup *sc;
+	swp_entry_t entry;
+	unsigned long flags;
+};
+
 /*
  * SwapCgroup implements "lookup" and "exchange" operations.
  * In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
@@ -75,6 +82,34 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 	return sc + offset % SC_PER_PAGE;
 }
 
+static void swap_cgroup_iter_init(struct swap_cgroup_iter *iter, swp_entry_t ent)
+{
+	iter->entry = ent;
+	iter->sc = lookup_swap_cgroup(ent, &iter->ctrl);
+	spin_lock_irqsave(&iter->ctrl->lock, iter->flags);
+}
+
+static void swap_cgroup_iter_exit(struct swap_cgroup_iter *iter)
+{
+	spin_unlock_irqrestore(&iter->ctrl->lock, iter->flags);
+}
+
+/*
+ * swap_cgroup is stored in a kind of discontinuous array.  That is,
+ * they are continuous in one page, but not across page boundary.  And
+ * there is one lock for each page.
+ */
+static void swap_cgroup_iter_advance(struct swap_cgroup_iter *iter)
+{
+	iter->sc++;
+	iter->entry.val++;
+	if (!(((unsigned long)iter->sc) & PAGE_MASK)) {
+		spin_unlock_irqrestore(&iter->ctrl->lock, iter->flags);
+		iter->sc = lookup_swap_cgroup(iter->entry, &iter->ctrl);
+		spin_lock_irqsave(&iter->ctrl->lock, iter->flags);
+	}
+}
+
 /**
  * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
  * @ent: swap entry to be cmpxchged
@@ -87,20 +122,18 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new)
 {
-	struct swap_cgroup_ctrl *ctrl;
-	struct swap_cgroup *sc;
-	unsigned long flags;
+	struct swap_cgroup_iter iter;
 	unsigned short retval;
 
-	sc = lookup_swap_cgroup(ent, &ctrl);
+	swap_cgroup_iter_init(&iter, ent);
 
-	spin_lock_irqsave(&ctrl->lock, flags);
-	retval = sc->id;
+	retval = iter.sc->id;
 	if (retval == old)
-		sc->id = new;
+		iter.sc->id = new;
 	else
 		retval = 0;
-	spin_unlock_irqrestore(&ctrl->lock, flags);
+
+	swap_cgroup_iter_exit(&iter);
 	return retval;
 }
 
@@ -114,18 +147,15 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
  */
 unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
 {
-	struct swap_cgroup_ctrl *ctrl;
-	struct swap_cgroup *sc;
+	struct swap_cgroup_iter iter;
 	unsigned short old;
-	unsigned long flags;
 
-	sc = lookup_swap_cgroup(ent, &ctrl);
+	swap_cgroup_iter_init(&iter, ent);
 
-	spin_lock_irqsave(&ctrl->lock, flags);
-	old = sc->id;
-	sc->id = id;
-	spin_unlock_irqrestore(&ctrl->lock, flags);
+	old = iter.sc->id;
+	iter.sc->id = id;
 
+	swap_cgroup_iter_exit(&iter);
 	return old;
 }
 
-- 
2.8.1