linux-kernel - [PATCH v1 1/2] zsmalloc: zs_object

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Message-ID: <20220811153755.16102-2-avromanov@sberdevices.ru>
Date:   Thu, 11 Aug 2022 18:37:54 +0300
From:   Alexey Romanov <avromanov@...rdevices.ru>
To:     <minchan@...nel.org>, <senozhatsky@...omium.org>,
        <ngupta@...are.org>, <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...rdevices.ru>, Alexey Romanov <avromanov@...rdevices.ru>
Subject: [PATCH v1 1/2] zsmalloc: zs_object_copy: add clarifying comment

It's not obvious why kunmap_atomic(d_addr) call is needed.

Signed-off-by: Alexey Romanov <avromanov@...rdevices.ru>
---
 mm/zsmalloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 5d5fc04385b8..5efa8c592193 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1564,6 +1564,12 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 		d_off += size;
 		d_size -= size;
 
+		/* Calling kunmap_atomic(d_addr) is necessary. kunmap_atomic() calls
+		 * must occurs in reverse order of calls to kmap_atomic().
+		 * So, to call kunmap_atomic(s_addr) we should first call kunmap_atomic(d_addr).
+		 * For more details see:
+		 * https://lore.kernel.org/linux-mm/5512421D.4000603@samsung.com/
+		 */
 		if (s_off >= PAGE_SIZE) {
 			kunmap_atomic(d_addr);
 			kunmap_atomic(s_addr);
-- 
2.30.1