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

[David Hildenbrand]

On 26.10.20 12:54, Mike Rapoport wrote:
> On Mon, Oct 26, 2020 at 12:05:13PM +0100, David Hildenbrand wrote:
>> 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.
>  
> Hmm, I beleive you refer to moving kernel_map_pages() to snapshot.c,
> right?

Sorry, yes!


-- 
Thanks,

David / dhildenb