linux-kernel - Re: [PATCH] btrfs: Use readahead_batch

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Message-ID: <20210406194216.GP7604@twin.jikos.cz>
Date:   Tue, 6 Apr 2021 21:42:16 +0200
From:   David Sterba <dsterba@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] btrfs: Use readahead_batch_length

On Sun, Mar 21, 2021 at 09:03:11PM +0000, Matthew Wilcox (Oracle) wrote:
> Implement readahead_batch_length() to determine the number of bytes in
> the current batch of readahead pages and use it in btrfs.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

Thanks, I'll take it through my tree as btrfs is probably the only user
of the new helper. The MM list hasn't been CCed, I've added it now but I
think the patch is trivial enough and does not need another ack, so it's
just for the record.

> ---
>  fs/btrfs/extent_io.c    | 6 ++----
>  include/linux/pagemap.h | 9 +++++++++
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index e9837562f7d6..97ac4ddb2857 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4875,10 +4875,8 @@ void extent_readahead(struct readahead_control *rac)
>  	int nr;
>  
>  	while ((nr = readahead_page_batch(rac, pagepool))) {
> -		u64 contig_start = page_offset(pagepool[0]);
> -		u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1;
> -
> -		ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end);
> +		u64 contig_start = readahead_pos(rac);
> +		u64 contig_end = contig_start + readahead_batch_length(rac) - 1;
>  
>  		contiguous_readpages(pagepool, nr, contig_start, contig_end,
>  				&em_cached, &bio, &bio_flags, &prev_em_start);
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 2cbfd4c36026..92939afd4944 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -1174,6 +1174,15 @@ static inline unsigned int readahead_count(struct readahead_control *rac)
>  	return rac->_nr_pages;
>  }
>  
> +/**
> + * readahead_batch_length - The number of bytes in the current batch.
> + * @rac: The readahead request.
> + */
> +static inline loff_t readahead_batch_length(struct readahead_control *rac)
> +{
> +	return rac->_batch_count * PAGE_SIZE;
> +}
> +
>  static inline unsigned long dir_pages(struct inode *inode)
>  {
>  	return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>

--