linux-kernel - Re: [PATCH 4/5] mm, highmem: makes flush_all_zero_pkmaps() return index of last flushed entry

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Date:	Mon, 29 Oct 2012 11:06:31 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/5] mm, highmem: makes flush_all_zero_pkmaps() return
 index of last flushed entry

On Mon, Oct 29, 2012 at 04:12:55AM +0900, Joonsoo Kim wrote:
> In current code, after flush_all_zero_pkmaps() is invoked,
> then re-iterate all pkmaps. It can be optimized if flush_all_zero_pkmaps()
> return index of flushed entry. With this index,
> we can immediately map highmem page to virtual address represented by index.
> So change return type of flush_all_zero_pkmaps()
> and return index of last flushed entry.
> 
> Signed-off-by: Joonsoo Kim <js1304@...il.com>
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index ef788b5..0683869 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -32,6 +32,7 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
>  
>  #ifdef CONFIG_HIGHMEM
>  #include <asm/highmem.h>
> +#define PKMAP_INDEX_INVAL (-1)

How about this?

#define PKMAP_INVALID_INDEX (-1)

>  
>  /* declarations for linux/mm/highmem.c */
>  unsigned int nr_free_highpages(void);
> diff --git a/mm/highmem.c b/mm/highmem.c
> index 731cf9a..65beb9a 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -106,10 +106,10 @@ struct page *kmap_to_page(void *vaddr)
>  	return virt_to_page(addr);
>  }
>  
> -static void flush_all_zero_pkmaps(void)
> +static int flush_all_zero_pkmaps(void)
>  {
>  	int i;
> -	int need_flush = 0;
> +	int index = PKMAP_INDEX_INVAL;
>  
>  	flush_cache_kmaps();
>  
> @@ -141,10 +141,12 @@ static void flush_all_zero_pkmaps(void)
>  			  &pkmap_page_table[i]);
>  
>  		set_page_address(page, NULL);
> -		need_flush = 1;
> +		index = i;

How about returning first free index instead of last one?
and update last_pkmap_nr to it.

>  	}
> -	if (need_flush)
> +	if (index != PKMAP_INDEX_INVAL)
>  		flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
> +
> +	return index;
>  }
>  
>  /**
> @@ -160,6 +162,7 @@ void kmap_flush_unused(void)
>  static inline unsigned long map_new_virtual(struct page *page)
>  {
>  	unsigned long vaddr;
> +	int index = PKMAP_INDEX_INVAL;
>  	int count;
>  
>  start:
> @@ -168,40 +171,45 @@ start:
>  	for (;;) {
>  		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
>  		if (!last_pkmap_nr) {
> -			flush_all_zero_pkmaps();
> -			count = LAST_PKMAP;
> +			index = flush_all_zero_pkmaps();
> +			if (index != PKMAP_INDEX_INVAL)
> +				break; /* Found a usable entry */
>  		}
> -		if (!pkmap_count[last_pkmap_nr])
> +		if (!pkmap_count[last_pkmap_nr]) {
> +			index = last_pkmap_nr;
>  			break;	/* Found a usable entry */
> -		if (--count)
> -			continue;
> -
> -		/*
> -		 * Sleep for somebody else to unmap their entries
> -		 */
> -		{
> -			DECLARE_WAITQUEUE(wait, current);
> -
> -			__set_current_state(TASK_UNINTERRUPTIBLE);
> -			add_wait_queue(&pkmap_map_wait, &wait);
> -			unlock_kmap();
> -			schedule();
> -			remove_wait_queue(&pkmap_map_wait, &wait);
> -			lock_kmap();
> -
> -			/* Somebody else might have mapped it while we slept */
> -			if (page_address(page))
> -				return (unsigned long)page_address(page);
> -
> -			/* Re-start */
> -			goto start;
>  		}
> +		if (--count == 0)
> +			break;
>  	}
> -	vaddr = PKMAP_ADDR(last_pkmap_nr);
> +
> +	/*
> +	 * Sleep for somebody else to unmap their entries
> +	 */
> +	if (index == PKMAP_INDEX_INVAL) {
> +		DECLARE_WAITQUEUE(wait, current);
> +
> +		__set_current_state(TASK_UNINTERRUPTIBLE);
> +		add_wait_queue(&pkmap_map_wait, &wait);
> +		unlock_kmap();
> +		schedule();
> +		remove_wait_queue(&pkmap_map_wait, &wait);
> +		lock_kmap();
> +
> +		/* Somebody else might have mapped it while we slept */
> +		vaddr = (unsigned long)page_address(page);
> +		if (vaddr)
> +			return vaddr;
> +
> +		/* Re-start */
> +		goto start;
> +	}
> +
> +	vaddr = PKMAP_ADDR(index);
>  	set_pte_at(&init_mm, vaddr,
> -		   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
> +		   &(pkmap_page_table[index]), mk_pte(page, kmap_prot));
>  
> -	pkmap_count[last_pkmap_nr] = 1;
> +	pkmap_count[index] = 1;
>  	set_page_address(page, (void *)vaddr);
>  
>  	return vaddr;
> -- 
> 1.7.9.5
> 
> --
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-- 
Kind regards,
Minchan Kim
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