Date:   Mon, 13 Feb 2023 00:28:15 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v13 03/12] splice: Do splice read from a buffered file
 without using ITER_PIPE
Message-ID: <Y+n0n2UE8BQa/OwW@infradead.org>
References: <20230209102954.528942-1-dhowells@redhat.com>
 <20230209102954.528942-4-dhowells@redhat.com>
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In-Reply-To: <20230209102954.528942-4-dhowells@redhat.com>
Precedence: bulk

> The code is loosely based on filemap_read() and might belong in
> mm/filemap.c with that as it needs to use filemap_get_pages().

Yes, I thunk it should go into filemap.c

> +	while (spliced < size &&
> +	       !pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
> +		struct pipe_buffer *buf = &pipe->bufs[pipe->head & (pipe->ring_size - 1)];

Can you please facto this calculation, that is also duplicated in patch
one into a helper?

static inline struct pipe_buffer *pipe_head_buf(struct pipe_inode_info *pipe)
{
	return &pipe->bufs[pipe->head & (pipe->ring_size - 1)];
}

> +	struct folio_batch fbatch;
> +	size_t total_spliced = 0, used, npages;
> +	loff_t isize, end_offset;
> +	bool writably_mapped;
> +	int i, error = 0;
> +
> +	struct kiocb iocb = {

Why the empty line before this declaration?

> +		.ki_filp	= in,
> +		.ki_pos		= *ppos,
> +	};

Also why doesn't this use init_sync_kiocb?

>  	if (in->f_flags & O_DIRECT)
>  		return generic_file_direct_splice_read(in, ppos, pipe, len, flags);
> +	return generic_file_buffered_splice_read(in, ppos, pipe, len, flags);

Btw, can we drop the verbose generic_file_ prefix here?

generic_file_buffered_splice_read really should be filemap_splice_read
and be in filemap.c.  generic_file_direct_splice_read I'd just name
direct_splice_read.