Re: [PATCH 5/7] page migration: synchronize from and to lists

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Fri, 28 Apr 2006 08:31:04 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> On Fri, 28 Apr 2006, KAMEZAWA Hiroyuki wrote:
> 
> > you should rotate "to" list in this case, I think.		
> 
> Hmmm.... Seems that the whole list scanning needs an overhaul. What do 
> you thinkg about this?
> 
maybe work, but complicated..
What benefits by this 1-1 ordering ?


-Kame


> 
> Rework main loop in migrate_pages()
> 
> Take pages off the "to" and "from" list in a consistent way so that 1-1
> relationships between pages on both lists can be maintained.
> 
> This also means that pages are not on any list while migration is attempted.
> Instead of "move_to_lru" we only need "to_lru".
> 
> Index: linux-2.6.17-rc2-mm1/mm/migrate.c
> ===================================================================
> --- linux-2.6.17-rc2-mm1.orig/mm/migrate.c	2006-04-28 06:56:36.856624280 -0700
> +++ linux-2.6.17-rc2-mm1/mm/migrate.c	2006-04-28 08:26:29.893711598 -0700
> @@ -82,9 +82,8 @@
>  	return 0;
>  }
>  
> -static inline void move_to_lru(struct page *page)
> +static inline void to_lru(struct page *page)
>  {
> -	list_del(&page->lru);
>  	if (PageActive(page)) {
>  		/*
>  		 * lru_cache_add_active checks that
> @@ -92,9 +91,9 @@
>  		 */
>  		ClearPageActive(page);
>  		lru_cache_add_active(page);
> -	} else {
> +	} else
>  		lru_cache_add(page);
> -	}
> +
>  	put_page(page);
>  }
>  
> @@ -110,7 +109,8 @@
>  	int count = 0;
>  
>  	list_for_each_entry_safe(page, page2, l, lru) {
> -		move_to_lru(page);
> +		list_del(&page->lru);
> +		to_lru(page);
>  		count++;
>  	}
>  	return count;
> @@ -532,36 +532,42 @@
>   * Return: Number of pages not migrated when "to" ran empty.
>   */
>  int migrate_pages(struct list_head *from, struct list_head *to,
> -		  struct list_head *moved, struct list_head *failed)
> +		  struct list_head *done, struct list_head *failed)
>  {
> -	int retry;
>  	int nr_failed = 0;
>  	int pass = 0;
> -	struct page *page;
> -	struct page *page2;
>  	int swapwrite = current->flags & PF_SWAPWRITE;
> -	int rc;
> +	int retry;
> +	struct list_head retry_to;
> +	struct list_head retry_from;
> +	struct list_head unused;
>  
>  	if (!swapwrite)
>  		current->flags |= PF_SWAPWRITE;
>  
> +	INIT_LIST_HEAD(&unused);
>  redo:
>  	retry = 0;
> +	INIT_LIST_HEAD(&retry_from);
> +	INIT_LIST_HEAD(&retry_to);
>  
> -	list_for_each_entry_safe(page, page2, from, lru) {
> -		struct page *newpage = NULL;
> +	while (!list_empty(from) && !list_empty(to)) {
> +		int rc = 0;
> +		struct page *page;
> +		struct page *newpage;
>  		struct address_space *mapping;
>  
>  		cond_resched();
>  
> -		rc = 0;
> +		page = lru_to_page(from);
> +		list_del(&page->lru);
> +		newpage = lru_to_page(to);
> +		list_del(&newpage->lru);
> +
>  		if (page_count(page) == 1)
>  			/* page was freed from under us. So we are done. */
>  			goto next;
>  
> -		if (list_empty(to))
> -			break;
> -
>  		/*
>  		 * Skip locked pages during the first two passes to give the
>  		 * functions holding the lock time to release the page. Later we
> @@ -585,7 +591,6 @@
>  		else if (PageWriteback(page))
>  				goto unlock_page;
>  
> -		newpage = lru_to_page(to);
>  		lock_page(newpage);
>  		/* Prepare mapping for the new page.*/
>  		newpage->index = page->index;
> @@ -610,32 +615,33 @@
>  		unlock_page(page);
>  
>  next:
> -		if (rc) {
> -			if (newpage) {
> -				newpage->mapping = NULL;
> -				list_move_tail(&newpage->lru, to);
> -			}
> +		if (likely(rc == 0)) {
> +			/* Successful migration. */
> +			to_lru(newpage);
> +			list_add(&page->lru, done);
> +		} else {
>  
> -			if (rc == -EAGAIN)
> +			newpage->mapping = NULL;
> +			if (rc == -EAGAIN) {
>  				/* Soft failure */
>  				retry++;
> -
> -			else {
> +				list_add(&newpage->lru, &retry_to);
> +				list_add(&page->lru, &retry_from);
> +			} else {
>  				/* Permanent failure */
> -				list_move(&page->lru, failed);
>  				nr_failed++;
> +				list_add(&newpage->lru, &unused);
> +				list_add(&page->lru, failed);
>  			}
> -		} else {
> -			if (newpage)
> -				/* Successful migration. Return page to LRU */
> -				move_to_lru(newpage);
> -
> -			list_move(&page->lru, moved);
>  		}
>  	}
> +	list_splice(&retry_to, to);
> +	list_splice(&retry_from, from);
> +
>  	if (retry && pass++ < 10)
>  		goto redo;
>  
> +	list_splice(&unused, to);
>  	if (!swapwrite)
>  		current->flags &= ~PF_SWAPWRITE;
>  
> 

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