From: Alexey Romanov Date: Thu, 11 Aug 2022 15:37:54 +0000 (+0300) Subject: zsmalloc: zs_object_copy: add clarifying comment X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=050a388b7f05b13dbcc5b6f14a4c7565a69a5020;p=linux.git 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. [akpm@linux-foundation.org: tweak comment layout] 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 --- diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 907c9b1e1e614..09ab91a3fa3f6 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1555,6 +1555,13 @@ 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);