Messages in this thread | | | Date | Wed, 30 Mar 2022 19:28:27 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v6 1/4] mm: hugetlb_vmemmap: introduce STRUCT_PAGE_SIZE_IS_POWER_OF_2 |
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On Wed, 30 Mar 2022 23:37:42 +0800 Muchun Song <songmuchun@bytedance.com> wrote:
> If the size of "struct page" is not the power of two and this > feature is enabled,
What is "this feature"? Let's spell it out?
> then the vmemmap pages of HugeTLB will be > corrupted after remapping (panic is about to happen in theory). > But this only exists when !CONFIG_MEMCG && !CONFIG_SLUB on > x86_64. However, it is not a conventional configuration nowadays. > So it is not a real word issue, just the result of a code review. > But we have to prevent anyone from configuring that combined > configuration. In order to avoid many checks like "is_power_of_2 > (sizeof(struct page))" through mm/hugetlb_vmemmap.c. Introduce > STRUCT_PAGE_SIZE_IS_POWER_OF_2 to detect if the size of struct > page is power of 2 and make this feature depends on this new > macro. Then we could prevent anyone do any unexpected > configuration. > > ... > > --- /dev/null > +++ b/mm/struct_page_size.c > @@ -0,0 +1,20 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Generate definitions needed by the preprocessor. > + * This code generates raw asm output which is post-processed > + * to extract and format the required data. > + */ > + > +#define __GENERATING_STRUCT_PAGE_SIZE_IS_POWER_OF_2_H > +/* Include headers that define the enum constants of interest */ > +#include <linux/mm_types.h> > +#include <linux/kbuild.h> > +#include <linux/log2.h> > + > +int main(void) > +{ > + if (is_power_of_2(sizeof(struct page))) > + DEFINE(STRUCT_PAGE_SIZE_IS_POWER_OF_2, is_power_of_2(sizeof(struct page)));
Why not
DEFINE(STRUCT_PAGE_SIZE_IS_POWER_OF_2, 1);
?
> + return 0; > +} > -- > 2.11.0
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