Re: [PATCH v4] ceph: set io_pages bdi hint

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-01-10 at 14:17 +0100, Andreas Gerstmayr wrote:
> This patch sets the io_pages bdi hint based on the rsize mount option.
> Without this patch large buffered reads (request size > max readahead)
> are processed sequentially in chunks of the readahead size (i.e. read
> requests are sent out up to the readahead size, then the
> do_generic_file_read() function waits until the first page is received).
> 
> With this patch read requests are sent out at once up to the size
> specified in the rsize mount option (default: 64 MB).
> 
> Signed-off-by: Andreas Gerstmayr <andreas.gerstmayr@catalysts.cc>
> ---
> 
> Changes in v4:
>   - update documentation
> 
> (Note: This patch depends on kernel version 4.10-rc1)
> 
> 
>  Documentation/filesystems/ceph.txt | 5 ++---
>  fs/ceph/super.c                    | 8 ++++++++
>  fs/ceph/super.h                    | 4 ++--
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph.txt
> index f5306ee..0b302a1 100644
> --- a/Documentation/filesystems/ceph.txt
> +++ b/Documentation/filesystems/ceph.txt
> @@ -98,11 +98,10 @@ Mount Options
>  	size.
>  
>    rsize=X
> -	Specify the maximum read size in bytes.  By default there is no
> -	maximum.
> +	Specify the maximum read size in bytes.  Default: 64 MB.
>  
>    rasize=X
> -	Specify the maximum readahead.
> +	Specify the maximum readahead.  Default: 8 MB.
>  
>    mount_timeout=X
>  	Specify the timeout value for mount (in seconds), in the case
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 6bd20d7..a0a0b6d 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -952,6 +952,14 @@ static int ceph_register_bdi(struct super_block *sb,
>  		fsc->backing_dev_info.ra_pages =
>  			VM_MAX_READAHEAD * 1024 / PAGE_SIZE;
>  
> +	if (fsc->mount_options->rsize > fsc->mount_options->rasize &&
> +	    fsc->mount_options->rsize >= PAGE_SIZE)
> +		fsc->backing_dev_info.io_pages =
> +			(fsc->mount_options->rsize + PAGE_SIZE - 1)
> +			>> PAGE_SHIFT;
> +	else if (fsc->mount_options->rsize == 0)
> +		fsc->backing_dev_info.io_pages = ULONG_MAX;
> +
>  	err = bdi_register(&fsc->backing_dev_info, NULL, "ceph-%ld",
>  			   atomic_long_inc_return(&bdi_seq));
>  	if (!err)
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index 3373b61..88b2e6e 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -45,8 +45,8 @@
>  #define ceph_test_mount_opt(fsc, opt) \
>  	(!!((fsc)->mount_options->flags & CEPH_MOUNT_OPT_##opt))
>  
> -#define CEPH_RSIZE_DEFAULT             0           /* max read size */
> -#define CEPH_RASIZE_DEFAULT            (8192*1024) /* readahead */
> +#define CEPH_RSIZE_DEFAULT              (64*1024*1024) /* max read size */
> +#define CEPH_RASIZE_DEFAULT             (8192*1024)    /* max readahead */
>  #define CEPH_MAX_READDIR_DEFAULT        1024
>  #define CEPH_MAX_READDIR_BYTES_DEFAULT  (512*1024)
>  #define CEPH_SNAPDIRNAME_DEFAULT        ".snap"

Acked-by: Jeff Layton <jlayton@redhat.com>