Re: [PATCH 3/7] mm: remove GFP_HIGHUSER_PAGECACHE

[Mel Gorman <mel@csn.ul.ie>]

Hi Hugh,

On Thu, Nov 20, 2008 at 01:16:16AM +0000, Hugh Dickins wrote:
> GFP_HIGHUSER_PAGECACHE is just an alias for GFP_HIGHUSER_MOVABLE,
> making that harder to track down: remove it, and its out-of-work
> brothers GFP_NOFS_PAGECACHE and GFP_USER_PAGECACHE.
> 
> Since we're making that improvement to hotremove_migrate_alloc(),
> I think we can now also remove one of the "o"s from its comment.
> 

The use of GFP_HIGHUSER_PAGECACHE instead of GFP_HIGHUSER_MOVABLE was a
deliberate decision at the time. I do not have an exact patch to point
you at but the intention behind GFP_HIGHUSER_PAGECACHE was that it be
self-documenting. i.e. one could easily find what GFP placement decisions
have been made for page-cache allocations.

GFP_NOFS_PAGECACHE is redundant and should have been dropped around the
time grow_dev_page() stopped using GFP_NOFS. GFP_USER_PAGECACHE is
similarly useless as bdget() no longer uses it which it did during some
point of patch revision.

So, I'm happy with GFP_NOFS_PAGECACHE and GFP_USER_PAGECACHE going away and
it makes perfect sense. GFP_HIGHUSER_PAGECACHE I'm not as keen on backing
out. I like it's self-documenting aspect but aliases sometimes make peoples
teeth itch. If it's really hated, then could a comment to the affect of
"Marked movable for a page cache allocation" be placed near the call-sites
instead?


> Signed-off-by: Hugh Dickins <hugh@veritas.com>
> ---
> 
>  fs/inode.c          |    4 ++--
>  include/linux/gfp.h |    6 ------
>  mm/memory_hotplug.c |    9 +++------
>  3 files changed, 5 insertions(+), 14 deletions(-)
> 
> --- mmclean2/fs/inode.c	2008-11-19 15:25:12.000000000 +0000
> +++ mmclean3/fs/inode.c	2008-11-19 15:26:16.000000000 +0000
> @@ -164,7 +164,7 @@ struct inode *inode_init_always(struct s
>  	mapping->a_ops = &empty_aops;
>  	mapping->host = inode;
>  	mapping->flags = 0;
> -	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_PAGECACHE);
> +	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
>  	mapping->assoc_mapping = NULL;
>  	mapping->backing_dev_info = &default_backing_dev_info;
>  	mapping->writeback_index = 0;
> @@ -599,7 +599,7 @@ EXPORT_SYMBOL_GPL(inode_add_to_lists);
>   *	@sb: superblock
>   *
>   *	Allocates a new inode for given superblock. The default gfp_mask
> - *	for allocations related to inode->i_mapping is GFP_HIGHUSER_PAGECACHE.
> + *	for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE.
>   *	If HIGHMEM pages are unsuitable or it is known that pages allocated
>   *	for the page cache are not reclaimable or migratable,
>   *	mapping_set_gfp_mask() must be called with suitable flags on the
> --- mmclean2/include/linux/gfp.h	2008-11-19 15:25:12.000000000 +0000
> +++ mmclean3/include/linux/gfp.h	2008-11-19 15:26:16.000000000 +0000
> @@ -70,12 +70,6 @@ struct vm_area_struct;
>  #define GFP_HIGHUSER_MOVABLE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
>  				 __GFP_HARDWALL | __GFP_HIGHMEM | \
>  				 __GFP_MOVABLE)
> -#define GFP_NOFS_PAGECACHE	(__GFP_WAIT | __GFP_IO | __GFP_MOVABLE)
> -#define GFP_USER_PAGECACHE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
> -				 __GFP_HARDWALL | __GFP_MOVABLE)
> -#define GFP_HIGHUSER_PAGECACHE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
> -				 __GFP_HARDWALL | __GFP_HIGHMEM | \
> -				 __GFP_MOVABLE)
>  
>  #ifdef CONFIG_NUMA
>  #define GFP_THISNODE	(__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
> --- mmclean2/mm/memory_hotplug.c	2008-11-19 15:25:12.000000000 +0000
> +++ mmclean3/mm/memory_hotplug.c	2008-11-19 15:26:16.000000000 +0000
> @@ -626,15 +626,12 @@ int scan_lru_pages(unsigned long start, 
>  }
>  
>  static struct page *
> -hotremove_migrate_alloc(struct page *page,
> -			unsigned long private,
> -			int **x)
> +hotremove_migrate_alloc(struct page *page, unsigned long private, int **x)
>  {
> -	/* This should be improoooooved!! */
> -	return alloc_page(GFP_HIGHUSER_PAGECACHE);
> +	/* This should be improooooved!! */
> +	return alloc_page(GFP_HIGHUSER_MOVABLE);
>  }
>  
> -
>  #define NR_OFFLINE_AT_ONCE_PAGES	(256)
>  static int
>  do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> 
> --
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> 

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

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