linux-kernel - Re: [PATCH 3/6] kernel: remove iterator use outside the loop

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Message-Id: <20220301113436.5513-1-xiam0nd.tong@gmail.com>
Date:   Tue,  1 Mar 2022 19:34:36 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     gregkh@...uxfoundation.org
Cc:     arnd@...db.de, jakobkoschel@...il.com, jannh@...gle.com,
        keescook@...omium.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        netdev@...r.kernel.org, torvalds@...ux-foundation.org,
        xiam0nd.tong@...il.com
Subject: Re: [PATCH 3/6] kernel: remove iterator use outside the loop

On Tue, 1 Mar 2022 11:41:34 +0100, greg k-h wrote:
> On Tue, Mar 01, 2022 at 03:58:36PM +0800, Xiaomeng Tong wrote:
> > Demonstrations for:
> >  - list_for_each_entry_inside
> >  - list_for_each_entry_continue_inside
> >  - list_for_each_entry_safe_continue_inside
>
> This changelog does not make much sense at all.  Why are you making
> these changes and how are we to review them?  Same for the others in
> this series.
> 
> confused,

I'm sorry for have created the confusion. I made this patch to remove
the use of iterator (in this patch is "ext", "cur", "aux", "q") outside
the list_for_each_entry* loop, using the new *_inside macros instead
which are introduced in PATCH v2, and to prove the effectiveness of
the new macros.

The detail for create_mem_extents patch:

1. remove the iterator use outside the loop:
-		struct mem_extent *ext, *cur, *aux;

2. declare a ptr outside the loop and set NULL:
+		struct mem_extent *me = NULL;

3. repace list_for_each_entry with list_for_each_entry_inside, and pass
   a new argument (struct mem_extent) as the struct type.
+		list_for_each_entry_inside(ext, struct mem_extent, list, hook)

4. when we hit the break in list_for_each_entry, record the found iterator
   for lately use:
+			if (zone_start <= ext->end) {
+				me = ext;
 				break;
+			}

5. when we miss the break, the "me" is NULL and can be used to determine if
   we already found the "ext". And replace every "ext" use after the loop
   with "me".
-		if (&ext->hook == list || zone_end < ext->start) {
+		if (!me || zone_end < me->start) {


6. repace list_for_each_entry_safe_continue with
   list_for_each_entry_safe_continue_inside, and pass a new argument (me)
   as the iterator to start/continue with.
-		list_for_each_entry_safe_continue(cur, aux, list, hook) {
+		list_for_each_entry_safe_continue_inside(cur, aux, me, list, hook) {

Best regards,
--
Xiaomeng Tong