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To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <jens.axboe@oracle.com>, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] Add block device speciffic splice write method
References: <1224424858-3927-1-git-send-email-dmonakhov@openvz.org>
	<20081020174931.GH19428@kernel.dk> <20081020181156.GI19428@kernel.dk>
	<20081022223928.a6ce476f.akpm@linux-foundation.org>
From: Dmitri Monakhov <dmonakhov@openvz.org>
Date: Thu, 23 Oct 2008 12:41:03 +0400
In-Reply-To: <20081022223928.a6ce476f.akpm@linux-foundation.org> (Andrew Morton's message of "Wed\, 22 Oct 2008 22\:39\:28 -0700")
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Andrew Morton <akpm@linux-foundation.org> writes:

> On Mon, 20 Oct 2008 20:11:56 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
>
>> +ssize_t generic_file_splice_write_file_nolock(struct pipe_inode_info *pipe,
>> +					      struct file *out, loff_t *ppos,
>> +					      size_t len, unsigned int flags)
>> +{
>> +	struct address_space *mapping = out->f_mapping;
>> +	struct inode *inode = mapping->host;
>> +	struct splice_desc sd = {
>> +		.total_len = len,
>> +		.flags = flags,
>> +		.pos = *ppos,
>> +		.u.file = out,
>> +	};
>> +	ssize_t ret;
>> +
>> +	mutex_lock(&pipe->inode->i_mutex);
>> +	ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
>> +	mutex_unlock(&pipe->inode->i_mutex);
>> +
>> +	if (ret > 0) {
>> +		unsigned long nr_pages;
>> +
>> +		*ppos += ret;
>> +		nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
>> +
>> +		if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
>> +			int er;
>> +
>> +			er = sync_page_range_nolock(inode, mapping, *ppos, ret);
>> +			if (er)
>> +				ret = er;
>> +		}
>> +		balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
>> +	}
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(generic_file_splice_write_file_nolock);
>
> I don't think the balance_dirty_pages() is needed if we just did the
> sync_page_range().
I think so too, but I've done it in this way because all other writers
does it. 
>
>
> But really it'd be better if the throttling happened down in
> pipe_to_file(), on a per-page basis.  As it stands we can dirty an
> arbitrary number of pagecache pages without throttling.  I think?