From: Vlastimil Babka <vbabka@suse.cz>
To: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: mike.kravetz@oracle.com, 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 12:02:38 +0200 [thread overview]
Message-ID: <e0d384a7-34bc-43ce-dc20-db4808b0f736@suse.cz> (raw)
In-Reply-To: <20200714095713.GA86690@L-31X9LVDL-1304.local>
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.
next prev parent reply other threads:[~2020-07-14 10:02 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 [this message]
2020-07-14 21:12 ` Mike Kravetz
2020-07-15 3:46 ` Wei Yang
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