Re: [PATCH] maple_tree: fix the comment on maple_arange_64 size

[Wei Yang <richard.weiyang@gmail.com>]

On Wed, Jul 17, 2024 at 04:05:35AM +0100, Matthew Wilcox wrote:
>On Wed, Jul 17, 2024 at 03:03:13AM +0000, Wei Yang wrote:
>> On Wed, Jul 17, 2024 at 03:45:40AM +0100, Matthew Wilcox wrote:
>> >On Wed, Jul 17, 2024 at 02:41:26AM +0000, Wei Yang wrote:
>> >> On Wed, Jul 17, 2024 at 03:06:01AM +0100, Matthew Wilcox wrote:
>> >> >On Wed, Jul 17, 2024 at 01:41:42AM +0000, Wei Yang wrote:
>> >> >> The comment here describe the size of struct maple_arange_64.
>> >> >> 
>> >> >> The value here is not correct. Fix it with the correct value.
>> >> >
>> >> >You are wrong.
>> >> 
>> >> You mean the my value is wrong or my understanding is wrong? 
>> >
>> >Yes.
>> 
>> I don't get it.
>> 
>> Would you mind sharing some light on what 240 bytes stands for? I don't figure
>> out what size it represents.
>
>You first.  How did you determine the new value you used?

Sure.

My understanding of the comment is to represent the size of related data
structures, eg.  maple_node, maple_range_64 and maple_arange_64.

I add following code in test to the size of those structures.

diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index cea050675da2..93e77dea7f0b 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -3645,6 +3645,10 @@ static int __init maple_tree_seed(void)
                                5003, 5002};
        void *ptr = &set;

+       pr_info("\nsizeof struct maple_node %ld\n", sizeof(struct maple_node));
+       pr_info("\nsizeof struct maple_range_64 %ld\n", sizeof(struct maple_range_64));
+       pr_info("\nsizeof struct maple_arange_64 %ld\n", sizeof(struct maple_arange_64));

Then insert the test module.

$ sudo insmod lib/test_maple_tree.ko
[  152.152382]
[  152.152382] sizeof struct maple_node 256
[  152.153043]
[  152.153043] sizeof struct maple_range_64 256
[  152.153561]
[  152.153561] sizeof struct maple_arange_64 248

The first two is the same as in comment, while the third one is not the same.

The 248 for 64BIT comes from here.

For 32BIT, I copied structure definition to a user space source and compile
with -m32. The size of structure maple_arange_64 is 256. This is where 256
comes from.


-- 
Wei Yang
Help you, Help me