From 2450e66393de50b238f0c43ef0b07019068e3926 Mon Sep 17 00:00:00 2001 From: Alexey Romanov Date: Thu, 11 Aug 2022 18:37:54 +0300 Subject: [PATCH] zsmalloc: zs_object_copy: add clarifying comment Patch series "tidy up zsmalloc implementation" This patchset remove some unnecessary checks and adds a clarifying comment. While analysing zs_object_copy() function code, I spent some time to understand what the call kunmap_atomic(d_addr) is for. It seems that this point is not trivial and it is worth adding a comment. This patch (of 2): It's not obvious why kunmap_atomic(d_addr) call is needed. Link: https://lkml.kernel.org/r/20220811153755.16102-1-avromanov@sberdevices.ru Link: https://lkml.kernel.org/r/20220811153755.16102-2-avromanov@sberdevices.ru Signed-off-by: Alexey Romanov Cc: Minchan Kim Cc: Sergey Senozhatsky Cc: Nitin Gupta Signed-off-by: Andrew Morton --- mm/zsmalloc.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 907c9b1e1e61..7cbfdaa315c0 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1555,6 +1555,12 @@ 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); -- 2.50.1