linux-kernel - Re: [PATCH v2 1/5] hugetlb: use page.private for hugetlb specific page flags

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Message-ID: <01499168-dcd3-7302-b9b6-977bd4fd594f@oracle.com>
Date:   Wed, 20 Jan 2021 10:12:21 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...nel.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/5] hugetlb: use page.private for hugetlb specific
 page flags

On 1/20/21 1:30 AM, Oscar Salvador wrote:
> On Tue, Jan 19, 2021 at 05:30:45PM -0800, Mike Kravetz wrote:
>> + * Macros to create test, set and clear function definitions for
>> + * hugetlb specific page flags.
>> + */
>> +#ifdef CONFIG_HUGETLB_PAGE
>> +#define TESTHPAGEFLAG(uname, flname)				\
>> +static inline int HPage##uname(struct page *page)		\
>> +	{ BUILD_BUG_ON(sizeof_field(struct page, private) *	\
>> +			BITS_PER_BYTE < __NR_HPAGEFLAGS);	\
>> +	return test_bit(HPG_##flname, &(page->private)); }
>> +
>> +#define SETHPAGEFLAG(uname, flname)				\
>> +static inline void SetHPage##uname(struct page *page)		\
>> +	{ set_bit(HPG_##flname, &(page->private)); }
>> +
>> +#define CLEARHPAGEFLAG(uname, flname)				\
>> +static inline void ClearHPage##uname(struct page *page)		\
>> +	{ clear_bit(HPG_##flname, &(page->private)); }
>> +#else
>> +#define TESTHPAGEFLAG(uname, flname)				\
>> +static inline int HPage##uname(struct page *page)		\
>> +	{ BUILD_BUG_ON(sizeof_field(struct page, private) *	\
>> +			BITS_PER_BYTE < __NR_HPAGEFLAGS);	\
>> +	return 0 }
> 
> You missed a ";" right there.

Thanks.  I made that typo when fixing up some trivial checkpatch warnings.
Lesson learned (again), nothing is too trivial not to introduce erros.

> I might be missing something, but I do not think we need a BUILD_BUG_ON there
> when CONFIG_HUGETLB_PAGE is not set?
> Actually, would make more sense to move the BUILD_BUG_ON from above to
> hugetlb_init?

Yes, hugetlb_init is a better location for the BUILD_BUG_ON.  I initially
put it there before creating the !CONFIG_HUGETLB_PAGE version of the macros.
With the !CONFIG_HUGETLB_PAGE versions, none of the flags are ever used so
it is OK if the BUILD_BUG_ON is not included if !CONFIG_HUGETLB_PAGE.

-- 
Mike Kravetz