Re: [PATCH 1/4] mm: introduce debug_pagealloc_map_pages() helper

[David Hildenbrand]

On 25.10.20 11:15, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> 
> When CONFIG_DEBUG_PAGEALLOC is enabled, it unmaps pages from the
> kernel direct mapping after free_pages(). The pages than need to be
> mapped back before they could be used. Theese mapping operations use 
> __kernel_map_pages() guarded with with debug_pagealloc_enabled().
> 
> The only place that calls __kernel_map_pages() without checking
> whether DEBUG_PAGEALLOC is enabled is the hibernation code that
> presumes availability of this function when ARCH_HAS_SET_DIRECT_MAP
> is set. Still, on arm64, __kernel_map_pages() will bail out when
> DEBUG_PAGEALLOC is not enabled but set_direct_map_invalid_noflush()
> may render some pages not present in the direct map and hibernation
> code won't be able to save such pages.
> 
> To make page allocation debugging and hibernation interaction more
> robust, the dependency on DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP
> has to be made more explicit.
> 
> Start with combining the guard condition and the call to 
> __kernel_map_pages() into a single debug_pagealloc_map_pages()
> function to emphasize that __kernel_map_pages() should not be called
> without DEBUG_PAGEALLOC and use this new function to map/unmap pages
> when page allocation debug is enabled.
> 
> As the only remaining user of kernel_map_pages() is the hibernation
> code, mode that function into kernel/power/snapshot.c closer to a
> caller.

s/mode/move/

> 
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> --- 
> include/linux/mm.h      | 16 +++++++--------- kernel/power/snapshot.c
> | 11 +++++++++++ mm/memory_hotplug.c     |  3 +-- mm/page_alloc.c
> |  6 ++---- mm/slab.c               |  8 +++----- 5 files changed, 24
> insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h index
> ef360fe70aaf..14e397f3752c 100644 --- a/include/linux/mm.h +++
> b/include/linux/mm.h @@ -2927,21 +2927,19 @@ static inline bool
> debug_pagealloc_enabled_static(void) #if
> defined(CONFIG_DEBUG_PAGEALLOC) ||
> defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) extern void
> __kernel_map_pages(struct page *page, int numpages, int enable);
> 
> -/* - * When called in DEBUG_PAGEALLOC context, the call should most
> likely be - * guarded by debug_pagealloc_enabled() or
> debug_pagealloc_enabled_static() - */ -static inline void 
> -kernel_map_pages(struct page *page, int numpages, int enable) 
> +static inline void debug_pagealloc_map_pages(struct page *page, +
> int numpages, int enable) { -	__kernel_map_pages(page, numpages,
> enable); +	if (debug_pagealloc_enabled_static()) +
> __kernel_map_pages(page, numpages, enable); } + #ifdef
> CONFIG_HIBERNATION extern bool kernel_page_present(struct page
> *page); #endif	/* CONFIG_HIBERNATION */ #else	/*
> CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */ -static
> inline void -kernel_map_pages(struct page *page, int numpages, int
> enable) {} +static inline void debug_pagealloc_map_pages(struct page
> *page, +					     int numpages, int enable) {} #ifdef
> CONFIG_HIBERNATION static inline bool kernel_page_present(struct page
> *page) { return true; } #endif	/* CONFIG_HIBERNATION */ diff --git
> a/kernel/power/snapshot.c b/kernel/power/snapshot.c index
> 46b1804c1ddf..fa499466f645 100644 --- a/kernel/power/snapshot.c +++
> b/kernel/power/snapshot.c @@ -76,6 +76,17 @@ static inline void
> hibernate_restore_protect_page(void *page_address) {} static inline
> void hibernate_restore_unprotect_page(void *page_address) {} #endif
> /* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */
> 
> +#if defined(CONFIG_DEBUG_PAGEALLOC) ||
> defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) +static inline void 
> +kernel_map_pages(struct page *page, int numpages, int enable) +{ +
> __kernel_map_pages(page, numpages, enable); +} +#else +static inline
> void +kernel_map_pages(struct page *page, int numpages, int enable)
> {} +#endif +

That change should go into a separate patch.


For the debug_pagealloc_map_pages() parts

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>


-- 
Thanks,

David / dhildenb