linux-kernel - [PATCH v5 2/5] Revert "frontswap: simplify frontswap_register

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Message-ID: <20220915035003.3347466-3-liushixin2@huawei.com>
Date:   Thu, 15 Sep 2022 11:50:00 +0800
From:   Liu Shixin <liushixin2@...wei.com>
To:     Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        "Christoph Hellwig" <hch@....de>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Liu Shixin <liushixin2@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: [PATCH v5 2/5] Revert "frontswap: simplify frontswap_register_ops"

This reverts commit f328c1d16e4c764992895ac9c9425cea861b2ca0.

Since we are supported to delay zswap initializaton, we need to invoke
ops->init for the swap device which is already online when register
backend.

Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 mm/frontswap.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 279e55b4ed87..aa3a1e3ddf91 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -96,11 +96,53 @@ static inline void inc_frontswap_invalidates(void) { }
  */
 int frontswap_register_ops(const struct frontswap_ops *ops)
 {
+	DECLARE_BITMAP(a, MAX_SWAPFILES);
+	DECLARE_BITMAP(b, MAX_SWAPFILES);
+	struct swap_info_struct *si;
+	unsigned int i;
+
 	if (frontswap_ops)
 		return -EINVAL;
 
+	bitmap_zero(a, MAX_SWAPFILES);
+	bitmap_zero(b, MAX_SWAPFILES);
+
+	spin_lock(&swap_lock);
+	plist_for_each_entry(si, &swap_active_head, list) {
+		if (!WARN_ON(!si->frontswap_map))
+			__set_bit(si->type, a);
+	}
+	spin_unlock(&swap_lock);
+
+	/* the new ops needs to know the currently active swap devices */
+	for_each_set_bit(i, a, MAX_SWAPFILES)
+		ops->init(i);
+
 	frontswap_ops = ops;
 	static_branch_inc(&frontswap_enabled_key);
+
+	spin_lock(&swap_lock);
+	plist_for_each_entry(si, &swap_active_head, list) {
+		if (si->frontswap_map)
+			__set_bit(si->type, b);
+	}
+	spin_unlock(&swap_lock);
+
+	/*
+	 * On the very unlikely chance that a swap device was added or
+	 * removed between setting the "a" list bits and the ops init
+	 * calls, we re-check and do init or invalidate for any changed
+	 * bits.
+	 */
+	if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
+		for (i = 0; i < MAX_SWAPFILES; i++) {
+			if (!test_bit(i, a) && test_bit(i, b))
+				ops->init(i);
+			else if (test_bit(i, a) && !test_bit(i, b))
+				ops->invalidate_area(i);
+		}
+	}
+
 	return 0;
 }
 
-- 
2.25.1