From: Mike Kravetz <mike.kravetz@oracle.com>
To: Vlastimil Babka <vbabka@suse.cz>,
Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/hugetlb: hide nr_nodes in the internal of for_each_node_mask_to_[alloc|free]
Date: Tue, 14 Jul 2020 14:12:03 -0700 [thread overview]
Message-ID: <694bb1ac-4f9c-a6a5-7c87-1fc0cdd948a6@oracle.com> (raw)
In-Reply-To: <e0d384a7-34bc-43ce-dc20-db4808b0f736@suse.cz>
On 7/14/20 3:02 AM, Vlastimil Babka wrote:
> On 7/14/20 11:57 AM, Wei Yang wrote:
>> On Tue, Jul 14, 2020 at 11:22:03AM +0200, Vlastimil Babka wrote:
>>> On 7/14/20 11:13 AM, Vlastimil Babka wrote:
>>>> On 7/14/20 9:34 AM, Wei Yang wrote:
>>>>> The second parameter of for_each_node_mask_to_[alloc|free] is a loop
>>>>> variant, which is not used outside of loop iteration.
>>>>>
>>>>> Let's hide this.
>>>>>
>>>>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>>>>> ---
>>>>> mm/hugetlb.c | 38 ++++++++++++++++++++------------------
>>>>> 1 file changed, 20 insertions(+), 18 deletions(-)
>>>>>
>>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>>>> index 57ece74e3aae..9c3d15fb317e 100644
>>>>> --- a/mm/hugetlb.c
>>>>> +++ b/mm/hugetlb.c
>>>>> @@ -1196,17 +1196,19 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>>>>> return nid;
>>>>> }
>>>>>
>>>>> -#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask) \
>>>>> - for (nr_nodes = nodes_weight(*mask); \
>>>>> - nr_nodes > 0 && \
>>>>> +#define for_each_node_mask_to_alloc(hs, node, mask) \
>>>>> + int __nr_nodes; \
>>>>> + for (__nr_nodes = nodes_weight(*mask); \
>>>>
>>>> The problem with this is that if I use the macro twice in the same block, this
>>>> will redefine __nr_nodes and fail to compile, no?
>>>> In that case it's better to avoid setting up this trap, IMHO.
>>>
>>> Ah, and it will also generate the following warning, if the use of for_each*
>>> macro is not the first thing after variable declarations, but there's another
>>> statement before:
>>>
>>> warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
>>>
>>> Instead we should switch to C99 and declare it as "for (int __nr_nodes" :P
>>
>> Hmm... I tried what you suggested, but compiler complains.
>>
>> 'for' loop initial declarations are only allowed in C99 or C11 mode
>
> Yes, by "we should switch to C99" I meant that the kernel kbuild system would
> need to switch. Not a trivial change...
> Without that, I don't see how your patch is possible to do safely.
Vlastimil, thanks for pointing out future potential issues with this patch.
I likely would have missed that.
Wei, thanks for taking the time to put together the patch. However, I tend
to agree with Vlastimil's assesment. The cleanup is not worth the risk of
running into issues if someone uses multiple instances of the macro.
--
Mike Kravetz
next prev parent reply other threads:[~2020-07-14 21:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-14 7:34 [PATCH] mm/hugetlb: hide nr_nodes in the internal of for_each_node_mask_to_[alloc|free] Wei Yang
2020-07-14 8:37 ` Pankaj Gupta
2020-07-14 9:13 ` Vlastimil Babka
2020-07-14 9:22 ` Vlastimil Babka
2020-07-14 9:50 ` Wei Yang
2020-07-14 9:57 ` Wei Yang
2020-07-14 10:02 ` Vlastimil Babka
2020-07-14 21:12 ` Mike Kravetz [this message]
2020-07-15 3:46 ` Wei Yang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=694bb1ac-4f9c-a6a5-7c87-1fc0cdd948a6@oracle.com \
--to=mike.kravetz@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=richard.weiyang@linux.alibaba.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).