Re: [RFC 10/16] Variable Order Page Cache: Readahead fixups

[mel@skynet.ie (Mel Gorman)]

On (22/04/07 23:49), Christoph Lameter didst pronounce:
> Variable Order Page Cache: Readahead fixups
> 
> Readahead is now dependent on the page size. For larger page sizes
> we want less readahead.
> 
> Add a parameter to max_sane_readahead specifying the page order
> and update the code in mm/readahead.c to be aware of variant
> page sizes.
> 
> Mark the 2M readahead constant as a potential future problem.
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> ---
>  include/linux/mm.h |    2 +-
>  mm/fadvise.c       |    5 +++--
>  mm/filemap.c       |    5 +++--
>  mm/madvise.c       |    4 +++-
>  mm/readahead.c     |   20 +++++++++++++-------
>  5 files changed, 23 insertions(+), 13 deletions(-)
> 
> Index: linux-2.6.21-rc7/include/linux/mm.h
> ===================================================================
> --- linux-2.6.21-rc7.orig/include/linux/mm.h	2007-04-22 21:48:22.000000000 -0700
> +++ linux-2.6.21-rc7/include/linux/mm.h	2007-04-22 22:04:44.000000000 -0700
> @@ -1104,7 +1104,7 @@ unsigned long page_cache_readahead(struc
>  			  unsigned long size);
>  void handle_ra_miss(struct address_space *mapping, 
>  		    struct file_ra_state *ra, pgoff_t offset);
> -unsigned long max_sane_readahead(unsigned long nr);
> +unsigned long max_sane_readahead(unsigned long nr, int order);
>  
>  /* Do stack extension */
>  extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
> Index: linux-2.6.21-rc7/mm/fadvise.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/mm/fadvise.c	2007-04-22 21:47:41.000000000 -0700
> +++ linux-2.6.21-rc7/mm/fadvise.c	2007-04-22 22:04:44.000000000 -0700
> @@ -86,10 +86,11 @@ asmlinkage long sys_fadvise64_64(int fd,
>  		nrpages = end_index - start_index + 1;
>  		if (!nrpages)
>  			nrpages = ~0UL;
> -		
> +

Whitespace mangling. Your update is right, but maybe not the patch for
it.

>  		ret = force_page_cache_readahead(mapping, file,
>  				start_index,
> -				max_sane_readahead(nrpages));
> +				max_sane_readahead(nrpages,
> +					mapping->order));
>  		if (ret > 0)
>  			ret = 0;
>  		break;
> Index: linux-2.6.21-rc7/mm/filemap.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/mm/filemap.c	2007-04-22 22:03:09.000000000 -0700
> +++ linux-2.6.21-rc7/mm/filemap.c	2007-04-22 22:04:44.000000000 -0700
> @@ -1256,7 +1256,7 @@ do_readahead(struct address_space *mappi
>  		return -EINVAL;
>  
>  	force_page_cache_readahead(mapping, filp, index,
> -					max_sane_readahead(nr));
> +				max_sane_readahead(nr, mapping->order));
>  	return 0;
>  }
>  
> @@ -1391,7 +1391,8 @@ retry_find:
>  			count_vm_event(PGMAJFAULT);
>  		}
>  		did_readaround = 1;
> -		ra_pages = max_sane_readahead(file->f_ra.ra_pages);
> +		ra_pages = max_sane_readahead(file->f_ra.ra_pages,
> +							mapping->order);
>  		if (ra_pages) {
>  			pgoff_t start = 0;
>  
> Index: linux-2.6.21-rc7/mm/madvise.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/mm/madvise.c	2007-04-22 21:47:41.000000000 -0700
> +++ linux-2.6.21-rc7/mm/madvise.c	2007-04-22 22:04:44.000000000 -0700
> @@ -105,7 +105,9 @@ static long madvise_willneed(struct vm_a
>  	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
>  
>  	force_page_cache_readahead(file->f_mapping,
> -			file, start, max_sane_readahead(end - start));
> +			file, start,
> +			max_sane_readahead(end - start,
> +				file->f_mapping->order));
>  	return 0;
>  }
>  
> Index: linux-2.6.21-rc7/mm/readahead.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/mm/readahead.c	2007-04-22 21:47:41.000000000 -0700
> +++ linux-2.6.21-rc7/mm/readahead.c	2007-04-22 22:06:47.000000000 -0700
> @@ -152,7 +152,7 @@ int read_cache_pages(struct address_spac
>  			put_pages_list(pages);
>  			break;
>  		}
> -		task_io_account_read(PAGE_CACHE_SIZE);
> +		task_io_account_read(page_cache_size(mapping));
>  	}
>  	pagevec_lru_add(&lru_pvec);
>  	return ret;
> @@ -276,7 +276,7 @@ __do_page_cache_readahead(struct address
>  	if (isize == 0)
>  		goto out;
>  
> - 	end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
> + 	end_index = page_cache_index(mapping, isize - 1);
>  
>  	/*
>  	 * Preallocate as many pages as we will need.
> @@ -330,7 +330,11 @@ int force_page_cache_readahead(struct ad
>  	while (nr_to_read) {
>  		int err;
>  
> -		unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
> +		/*
> +		 * FIXME: Note the 2M constant here that may prove to
> +		 * be a problem if page sizes become bigger than one megabyte.
> +		 */
> +		unsigned long this_chunk = page_cache_index(mapping, 2 * 1024 * 1024);
>

Should readahead just be disabled when the compound page size is as
large or larger than what readahead normally reads?

>  		if (this_chunk > nr_to_read)
>  			this_chunk = nr_to_read;
> @@ -570,11 +574,13 @@ void handle_ra_miss(struct address_space
>  }
>  
>  /*
> - * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
> + * Given a desired number of page order readahead pages, return a
>   * sensible upper limit.
>   */
> -unsigned long max_sane_readahead(unsigned long nr)
> +unsigned long max_sane_readahead(unsigned long nr, int order)
>  {
> -	return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)
> -		+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
> +	unsigned long base_pages = node_page_state(numa_node_id(), NR_INACTIVE)
> +			+ node_page_state(numa_node_id(), NR_FREE_PAGES);
> +
> +	return min(nr, (base_pages / 2) >> order);
>  }

-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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