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Date:	Mon, 1 Sep 2014 09:53:01 +0200
From:	Jan Kara <jack@...e.cz>
To:	Gioh Kim <gioh.kim@....com>
Cc:	Jan Kara <jack@...e.cz>, Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <js1304@...il.com>,
	이건호 <gunho.lee@....com>
Subject: Re: [PATCHv3 1/3] fs/buffer.c: allocate buffer cache with user
 specific flag

On Fri 29-08-14 13:48:27, Gioh Kim wrote:
> What about below?: add gfp for __getblk_slow, change __getblk into __getblk_gfp,
> getblk_unmovable and __getblk are, I think, symmetric.
> 
> If you say OK, I'm going to send v4 with tabs ;-)
  Yes, this looks like what I wanted. I've just spotted two typos in
comments and one function which should be inline (see below). Thanks for
work!

								Honza
 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 8f05111..21711c78 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -993,7 +993,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
>   */
>  static int
>  grow_dev_page(struct block_device *bdev, sector_t block,
> -               pgoff_t index, int size, int sizebits)
> +             pgoff_t index, int size, int sizebits, gfp_t gfp)
>  {
>         struct inode *inode = bdev->bd_inode;
>         struct page *page;
> @@ -1002,10 +1002,10 @@ grow_dev_page(struct block_device *bdev, sector_t block,
>         int ret = 0;            /* Will call free_more_memory() */
>         gfp_t gfp_mask;
> 
> -       gfp_mask = mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS;
> -       gfp_mask |= __GFP_MOVABLE;
> +       gfp_mask = (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS) | gfp;
> +
>         /*
> -        * XXX: __getblk_slow() can not really deal with failure and
> +        * XXX: __getblk_gfp() can not really deal with failure and
  You can leave __getblk_slow() here I believe.


>          * will endlessly loop on improvised global reclaim.  Prefer
>          * looping in the allocator rather than here, at least that
>          * code knows what it's doing.
> @@ -1058,7 +1058,7 @@ failed:
>   * that page was dirty, the buffers are set dirty also.
>   */
>  static int
> -grow_buffers(struct block_device *bdev, sector_t block, int size)
> +grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
>  {
>         pgoff_t index;
>         int sizebits;
> @@ -1085,11 +1085,12 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
>         }
> 
>         /* Create a page with the proper size buffers.. */
> -       return grow_dev_page(bdev, block, index, size, sizebits);
> +       return grow_dev_page(bdev, block, index, size, sizebits, gfp);
>  }
> 
> -static struct buffer_head *
> -__getblk_slow(struct block_device *bdev, sector_t block, int size)
> +struct buffer_head *
> +__getblk_slow(struct block_device *bdev, sector_t block,
> +            unsigned size, gfp_t gfp)
>  {
>         /* Size must be multiple of hard sectorsize */
>         if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
> @@ -1111,13 +1112,14 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
>                 if (bh)
>                         return bh;
> 
> -               ret = grow_buffers(bdev, block, size);
> +               ret = grow_buffers(bdev, block, size, gfp);
>                 if (ret < 0)
>                         return NULL;
>                 if (ret == 0)
>                         free_more_memory();
>         }
>  }
> +EXPORT_SYMBOL(__getblk_slow);
> 
>  /*
>   * The relationship between dirty buffers and dirty pages:
> @@ -1371,24 +1373,25 @@ __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
>  EXPORT_SYMBOL(__find_get_block);
> 
>  /*
> - * __getblk will locate (and, if necessary, create) the buffer_head
> + * __getblk_gfp will locate (and, if necessary, create) the buffer_head
>   * which corresponds to the passed block_device, block and size. The
>   * returned buffer has its reference count incremented.
>   *
> - * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
> - * attempt is failing.  FIXME, perhaps?
> + * __getblk()_gfp will lock up the machine if grow_dev_page's
  _gfp should be before () in the line above.

> + * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
>   */
>  struct buffer_head *
> -__getblk(struct block_device *bdev, sector_t block, unsigned size)
> +__getblk_gfp(struct block_device *bdev, sector_t block,
> +            unsigned size, gfp_t gfp)
>  {
>         struct buffer_head *bh = __find_get_block(bdev, block, size);
> 
>         might_sleep();
>         if (bh == NULL)
> -               bh = __getblk_slow(bdev, block, size);
> +               bh = __getblk_slow(bdev, block, size, gfp);
>         return bh;
>  }
> -EXPORT_SYMBOL(__getblk);
> +EXPORT_SYMBOL(__getblk_gfp);
> 
>  /*
>   * Do async read-ahead on a buffer..
> @@ -1410,18 +1413,39 @@ EXPORT_SYMBOL(__breadahead);
>   *  @size: size (in bytes) to read
>   *
>   *  Reads a specified block, and returns buffer head that contains it.
> + *  The page cache is allocated from movable area so that it can be migrated.
>   *  It returns NULL if the block was unreadable.
>   */
>  struct buffer_head *
>  __bread(struct block_device *bdev, sector_t block, unsigned size)
>  {
> -       struct buffer_head *bh = __getblk(bdev, block, size);
> +       return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
> +}
> +EXPORT_SYMBOL(__bread);
  This can be just inline defined in buffer_head.h.


> +
> +/**
> + *  __bread_gfp() - reads a specified block and returns the bh
> + *  @bdev: the block_device to read from
> + *  @block: number of block
> + *  @size: size (in bytes) to read
> + *  @gfp: page allocation flag
> + *
> + *  Reads a specified block, and returns buffer head that contains it.
> + *  The page cache can be allocated from non-movable area
> + *  not to prevent page migration if you set gfp to zero.
> + *  It returns NULL if the block was unreadable.
> + */
> +struct buffer_head *
> +__bread_gfp(struct block_device *bdev, sector_t block,
> +                  unsigned size, gfp_t gfp)
> +{
> +       struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
> 
>         if (likely(bh) && !buffer_uptodate(bh))
>                 bh = __bread_slow(bh);
>         return bh;
>  }
> -EXPORT_SYMBOL(__bread);
> +EXPORT_SYMBOL(__bread_gfp);
> 
>  /*
>   * invalidate_bh_lrus() is called rarely - but not only at unmount.
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 324329c..6073f5d 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -175,12 +175,14 @@ void __wait_on_buffer(struct buffer_head *);
>  wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
>  struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
>                         unsigned size);
> -struct buffer_head *__getblk(struct block_device *bdev, sector_t block,
> -                       unsigned size);
> +struct buffer_head *__getblk_gfp(struct block_device *bdev, sector_t block,
> +                                 unsigned size, gfp_t gfp);
>  void __brelse(struct buffer_head *);
>  void __bforget(struct buffer_head *);
>  void __breadahead(struct block_device *, sector_t block, unsigned int size);
>  struct buffer_head *__bread(struct block_device *, sector_t block, unsigned size);
> +struct buffer_head *__bread_gfp(struct block_device *,
> +                               sector_t block, unsigned size, gfp_t gfp);
>  void invalidate_bh_lrus(void);
>  struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
>  void free_buffer_head(struct buffer_head * bh);
> @@ -295,7 +297,13 @@ static inline void bforget(struct buffer_head *bh)
>  static inline struct buffer_head *
>  sb_bread(struct super_block *sb, sector_t block)
>  {
> -       return __bread(sb->s_bdev, block, sb->s_blocksize);
> +       return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
> +}
> +
> +static inline struct buffer_head *
> +sb_bread_unmovable(struct super_block *sb, sector_t block)
> +{
> +       return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
>  }
> 
>  static inline void
> @@ -307,7 +315,7 @@ sb_breadahead(struct super_block *sb, sector_t block)
>  static inline struct buffer_head *
>  sb_getblk(struct super_block *sb, sector_t block)
>  {
> -       return __getblk(sb->s_bdev, block, sb->s_blocksize);
> +       return __getblk_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
>  }
> 
>  static inline struct buffer_head *
> @@ -344,6 +352,20 @@ static inline void lock_buffer(struct buffer_head *bh)
>                 __lock_buffer(bh);
>  }
> 
> +static inline struct buffer_head *getblk_unmovable(struct block_device *bdev,
> +                                                  sector_t block,
> +                                                  unsigned size)
> +{
> +       return __getblk_gfp(bdev, block, size, 0);
> +}
> +
> +static inline struct buffer_head *__getblk(struct block_device *bdev,
> +                                          sector_t block,
> +                                          unsigned size)
> +{
> +       return __getblk_gfp(bdev, block, size, __GFP_MOVABLE);
> +}
> +
>  extern int __set_page_dirty_buffers(struct page *page);
> 
>  #else /* CONFIG_BLOCK */
> --
> 1.7.9.5
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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