Re: [VFS PATCH] readahead: fix block ordering in __do_page_cache_readahead

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On Thu 14-01-16 15:58:53, Bob Peterson wrote:
> Hi,
> 
> I just ran into this today. I had temporarily disabled readpages in GFS2 in order to
> test something and discovered, to my surprise, that the block IOs were being issued
> in reverse order. In my case, the block_map function was called in reverse block
> order. In other words: lblock started at 8, then proceeded to 7, 6, 5, 4, 3, 2, 1, 0.
> So I surmised the order must be wrong. After a little digging, I whipped up this
> little patch. Can anyone out there corroborate this or tell me if I've I lost my mind?
> 
> Viro?
> 
> I'll add my Signed-off-by but I really haven't tested it or anything. It's kind of
> moot for file systems with readpages, but it might be worth doing.
> 
> Signed-off-by: Bob Peterson <rpeterso@xxxxxxxxxx>

The patch looks good to me. But I've added CC's to some relevant people.

								Honza

> ---
> diff --git a/mm/readahead.c b/mm/readahead.c
> index ba22d7f..b76fb34 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -185,7 +185,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
>  		if (!page)
>  			break;
>  		page->index = page_offset;
> -		list_add(&page->lru, &page_pool);
> +		list_add_tail(&page->lru, &page_pool);
>  		if (page_idx == nr_to_read - lookahead_size)
>  			SetPageReadahead(page);
>  		ret++;
> --
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-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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