Re: [PATCH 3.2.0-rc1 2/3] MM hook for page allocation and release

[KAMEZAWA Hiroyuki]

On Wed,  4 Jan 2012 19:21:55 +0200
Leonid Moiseichuk <leonid.moiseichuk@xxxxxxxxx> wrote:

> That is required by Used Memory Meter (UMM) pseudo-device
> to track memory utilization in system. It is expected that
> hook MUST be very light to prevent performance impact
> on the hot allocation path. Accuracy of number managed pages
> does not expected to be absolute but fact of allocation or
> deallocation must be registered.
> 
> Signed-off-by: Leonid Moiseichuk <leonid.moiseichuk@xxxxxxxxx>

I never like arbitrary hooks to alloc_pages().
Could you find another way ?

Hmm. memcg uses per-cpu counters for counting event of alloc/free and
trigger threashold check per 128 event on a cpu.


Thanks,
-Kame


> ---
>  include/linux/mm.h |   15 +++++++++++++++
>  mm/Kconfig         |    8 ++++++++
>  mm/page_alloc.c    |   31 +++++++++++++++++++++++++++++++
>  3 files changed, 54 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 3dc3a8c..d133f73 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1618,6 +1618,21 @@ extern int soft_offline_page(struct page *page, int flags);
>  
>  extern void dump_page(struct page *page);
>  
> +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
> +/*
> + * Hook function type which called when some pages allocated or released.
> + * Value of nr_pages is positive for post-allocation calls and negative
> + * after free.
> + */
> +typedef void (*mm_alloc_free_hook_t)(int nr_pages);
> +
> +/*
> + * Setups specified hook function for tracking pages allocation.
> + * Returns value of old hook to organize chains of calls if necessary.
> + */
> +mm_alloc_free_hook_t set_mm_alloc_free_hook(mm_alloc_free_hook_t hook);
> +#endif
> +
>  #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
>  extern void clear_huge_page(struct page *page,
>  			    unsigned long addr,
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 011b110..2aaa1e9 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -373,3 +373,11 @@ config CLEANCACHE
>  	  in a negligible performance hit.
>  
>  	  If unsure, say Y to enable cleancache
> +
> +config MM_ALLOC_FREE_HOOK
> +	bool "Enable callback support for pages allocation and releasing"
> +	default n
> +	help
> +	  Required for some features like used memory meter.
> +	  If unsure, say N to disable alloc/free hook.
> +
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9dd443d..9307800 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -236,6 +236,30 @@ static void set_pageblock_migratetype(struct page *page, int migratetype)
>  
>  bool oom_killer_disabled __read_mostly;
>  
> +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
> +static atomic_long_t alloc_free_hook __read_mostly = ATOMIC_LONG_INIT(0);
> +
> +mm_alloc_free_hook_t set_mm_alloc_free_hook(mm_alloc_free_hook_t hook)
> +{
> +	const mm_alloc_free_hook_t old_hook =
> +		(mm_alloc_free_hook_t)atomic_long_read(&alloc_free_hook);
> +
> +	atomic_long_set(&alloc_free_hook, (long)hook);
> +	pr_info("MM alloc/free hook set to 0x%p (was 0x%p)\n", hook, old_hook);
> +
> +	return old_hook;
> +}
> +EXPORT_SYMBOL(set_mm_alloc_free_hook);
> +
> +static inline void call_alloc_free_hook(int pages)
> +{
> +	const mm_alloc_free_hook_t hook =
> +		(mm_alloc_free_hook_t)atomic_long_read(&alloc_free_hook);
> +	if (hook)
> +		hook(pages);
> +}
> +#endif
> +
>  #ifdef CONFIG_DEBUG_VM
>  static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
>  {
> @@ -2298,6 +2322,10 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	put_mems_allowed();
>  
>  	trace_mm_page_alloc(page, order, gfp_mask, migratetype);
> +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
> +	call_alloc_free_hook(1 << order);
> +#endif
> +
>  	return page;
>  }
>  EXPORT_SYMBOL(__alloc_pages_nodemask);
> @@ -2345,6 +2373,9 @@ void __free_pages(struct page *page, unsigned int order)
>  			free_hot_cold_page(page, 0);
>  		else
>  			__free_pages_ok(page, order);
> +#ifdef CONFIG_MM_ALLOC_FREE_HOOK
> +		call_alloc_free_hook(-(1 << order));
> +#endif
>  	}
>  }
>  
> -- 
> 1.7.7.3
> 
> 

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