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Subject: Re: [PATCH] mm: Refactor readahead defines in mm.h
To:     Nikolay Borisov <nborisov@suse.com>, linux-mm@kvack.org,
        akpm@linux-foundation.org
Cc:     willy@infradead.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
References: <20181221144053.24318-1-nborisov@suse.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <6153943c-6f47-f6ba-e62b-cb2a6c05c59f@redhat.com>
Date:   Fri, 21 Dec 2018 17:03:28 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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On 21.12.18 15:40, Nikolay Borisov wrote:
> All users of VM_MAX_READAHEAD actually convert it to kbytes and then to
> pages. Define the macro explicitly as (SZ_128K / PAGE_SIZE). This
> simplifies the expression in every filesystem. Also rename the macro to
> VM_READAHEAD_PAGES to properly convey its meaning. Finally remove unused
> VM_MIN_READAHEAD
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  block/blk-core.c   | 3 +--
>  fs/9p/vfs_super.c  | 2 +-
>  fs/afs/super.c     | 2 +-
>  fs/btrfs/disk-io.c | 2 +-
>  fs/fuse/inode.c    | 2 +-
>  include/linux/mm.h | 4 ++--
>  6 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index deb56932f8c4..d25c8564a117 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1031,8 +1031,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id,
>  	if (!q->stats)
>  		goto fail_stats;
>  
> -	q->backing_dev_info->ra_pages =
> -			(VM_MAX_READAHEAD * 1024) / PAGE_SIZE;
> +	q->backing_dev_info->ra_pages = VM_READAHEAD_PAGES;
>  	q->backing_dev_info->capabilities = BDI_CAP_CGROUP_WRITEBACK;
>  	q->backing_dev_info->name = "block";
>  	q->node = node_id;
> diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
> index 48ce50484e80..10d3bd3f534b 100644
> --- a/fs/9p/vfs_super.c
> +++ b/fs/9p/vfs_super.c
> @@ -92,7 +92,7 @@ v9fs_fill_super(struct super_block *sb, struct v9fs_session_info *v9ses,
>  		return ret;
>  
>  	if (v9ses->cache)
> -		sb->s_bdi->ra_pages = (VM_MAX_READAHEAD * 1024)/PAGE_SIZE;
> +		sb->s_bdi->ra_pages = VM_READAHEAD_PAGES;
>  
>  	sb->s_flags |= SB_ACTIVE | SB_DIRSYNC;
>  	if (!v9ses->cache)
> diff --git a/fs/afs/super.c b/fs/afs/super.c
> index dcd07fe99871..e684f6769b15 100644
> --- a/fs/afs/super.c
> +++ b/fs/afs/super.c
> @@ -399,7 +399,7 @@ static int afs_fill_super(struct super_block *sb,
>  	ret = super_setup_bdi(sb);
>  	if (ret)
>  		return ret;
> -	sb->s_bdi->ra_pages	= VM_MAX_READAHEAD * 1024 / PAGE_SIZE;
> +	sb->s_bdi->ra_pages	= VM_READAHEAD_PAGES;
>  
>  	/* allocate the root inode and dentry */
>  	if (as->dyn_root) {
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 6d776717d8b3..ee47d8b5b50c 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2900,7 +2900,7 @@ int open_ctree(struct super_block *sb,
>  	sb->s_bdi->congested_fn = btrfs_congested_fn;
>  	sb->s_bdi->congested_data = fs_info;
>  	sb->s_bdi->capabilities |= BDI_CAP_CGROUP_WRITEBACK;
> -	sb->s_bdi->ra_pages = VM_MAX_READAHEAD * SZ_1K / PAGE_SIZE;
> +	sb->s_bdi->ra_pages = VM_READAHEAD_PAGES;
>  	sb->s_bdi->ra_pages *= btrfs_super_num_devices(disk_super);
>  	sb->s_bdi->ra_pages = max(sb->s_bdi->ra_pages, SZ_4M / PAGE_SIZE);
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 568abed20eb2..d3eab53a29b7 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1009,7 +1009,7 @@ static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)
>  	if (err)
>  		return err;
>  
> -	sb->s_bdi->ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_SIZE;
> +	sb->s_bdi->ra_pages = VM_READAHEAD_PAGES;
>  	/* fuse does it's own writeback accounting */
>  	sb->s_bdi->capabilities = BDI_CAP_NO_ACCT_WB | BDI_CAP_STRICTLIMIT;
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5411de93a363..1579082af177 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -26,6 +26,7 @@
>  #include <linux/page_ref.h>
>  #include <linux/memremap.h>
>  #include <linux/overflow.h>
> +#include <linux/sizes.h>
>  
>  struct mempolicy;
>  struct anon_vma;
> @@ -2396,8 +2397,7 @@ int __must_check write_one_page(struct page *page);
>  void task_dirty_inc(struct task_struct *tsk);
>  
>  /* readahead.c */
> -#define VM_MAX_READAHEAD	128	/* kbytes */
> -#define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
> +#define VM_READAHEAD_PAGES	(SZ_128K / PAGE_SIZE)
>  
>  int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
>  			pgoff_t offset, unsigned long nr_to_read);
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb