Re: [PATCH 4/5] Move the check for ra_pages after VM_SequentialReadHint()

[Fengguang Wu <fengguang.wu@intel.com>]

On Sat, Sep 22, 2012 at 04:03:13PM +0530, raghu.prabhu13@gmail.com wrote:
> From: Raghavendra D Prabhu <rprabhu@wnohang.net>
> 
> page_cache_sync_readahead checks for ra->ra_pages again, so moving the check
> after VM_SequentialReadHint.

Well it depends on what case you are optimizing for. I suspect there
are much more tmpfs users than VM_SequentialReadHint users. So this
change is actually not desirable wrt the more widely used cases.

Thanks,
Fengguang

> Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
> ---
>  mm/filemap.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 3843445..606a648 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1523,8 +1523,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>  	/* If we don't want any read-ahead, don't bother */
>  	if (VM_RandomReadHint(vma))
>  		return;
> -	if (!ra->ra_pages)
> -		return;
>  
>  	if (VM_SequentialReadHint(vma)) {
>  		page_cache_sync_readahead(mapping, ra, file, offset,
> @@ -1532,6 +1530,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>  		return;
>  	}
>  
> +	if (!ra->ra_pages)
> +		return;
> +
>  	/* Avoid banging the cache line if not needed */
>  	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
>  		ra->mmap_miss++;
> -- 
> 1.7.12.1
> 
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