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SubjectRe: [PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint()
On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
> page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.

NAK. This patch adds nothing but overheads.

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1566,8 +1566,6 @@ 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,
> @@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
> return;
> }
>
> + if (!ra->ra_pages)
> + return;
> +

page_cache_sync_readahead() has the same

if (!ra->ra_pages)
return;

So the patch adds the call into page_cache_sync_readahead() just to return..

Thanks,
Fengguang


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