On Wed, May 23, 2018 at 04:43:31PM +0200, Christoph Hellwig wrote:
> That way file systems don't have to go spotting for non-contiguous pages
> and work around them. It also kicks off I/O earlier, allowing it to
> finish earlier and reduce latency.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Looks ok, if anyone has a strong opinion they better yell soon...
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> mm/readahead.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index fa4d4b767130..e273f0de3376 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -140,8 +140,8 @@ static int read_pages(struct address_space *mapping, struct file *filp,
> }
>
> /*
> - * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
> - * the pages first, then submits them all for I/O. This avoids the very bad
> + * __do_page_cache_readahead() actually reads a chunk of disk. It allocates
> + * the pages first, then submits them for I/O. This avoids the very bad
> * behaviour which would occur if page allocations are causing VM writeback.
> * We really don't want to intermingle reads and writes like that.
> *
> @@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
> rcu_read_lock();
> page = radix_tree_lookup(&mapping->i_pages, page_offset);
> rcu_read_unlock();
> - if (page && !radix_tree_exceptional_entry(page))
> + if (page && !radix_tree_exceptional_entry(page)) {
> + /*
> + * Page already present? Kick off the current batch of
> + * contiguous pages before continuing with the next
> + * batch.
> + */
> + if (nr_pages)
> + read_pages(mapping, filp, &page_pool, nr_pages,
> + gfp_mask);
> + nr_pages = 0;
> continue;
> + }
>
> page = __page_cache_alloc(gfp_mask);
> if (!page)
> --
> 2.17.0
>
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