[Devel] Re: [PATCH 4/6] fuse: rework fuse_readpages()

[Miklos Szeredi]

Maxim Patlasov <mpatlasov at parallels.com> writes:

> The patch uses 'nr_pages' argument of fuse_readpages() as the heuristics for
> number of page pointers to allocate.
>
> This can be improved further by taking in consideration fc->max_read and gaps
> between page indices, but it's not clear wheteher it's worthy or not.
> ---
>  fs/fuse/file.c |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index c811f3d..9a6dcc6 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -641,6 +641,7 @@ struct fuse_fill_data {
>  	struct fuse_req *req;
>  	struct file *file;
>  	struct inode *inode;
> +	unsigned nr_pages;
>  };
>  
>  static int fuse_readpages_fill(void *_data, struct page *page)
> @@ -656,8 +657,10 @@ static int fuse_readpages_fill(void *_data, struct page *page)
>  	    (req->num_pages == FUSE_MAX_PAGES_PER_REQ ||
>  	     (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_read ||
>  	     req->pages[req->num_pages - 1]->index + 1 != page->index)) {
> +		int nr_alloc = min_t(unsigned, data->nr_pages,
> +				     FUSE_MAX_PAGES_PER_REQ);
>  		fuse_send_readpages(req, data->file);
> -		data->req = req = fuse_get_req_multipage(fc, FUSE_MAX_PAGES_PER_REQ);
> +		data->req = req = fuse_get_req_multipage(fc, nr_alloc);
>  		if (IS_ERR(req)) {
>  			unlock_page(page);
>  			return PTR_ERR(req);
> @@ -666,6 +669,7 @@ static int fuse_readpages_fill(void *_data, struct page *page)
>  	page_cache_get(page);


Okay, this is where things get hairy and where we should do something like:

	if (WARN_ON(req->num_pages >= req->max_pages))
		return -EIO;

>  	req->pages[req->num_pages] = page;
>  	req->num_pages++;
> +	data->nr_pages--;
>  	return 0;
>  }
>  
> @@ -676,6 +680,7 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
>  	struct fuse_conn *fc = get_fuse_conn(inode);
>  	struct fuse_fill_data data;
>  	int err;
> +	int nr_alloc = min_t(unsigned, nr_pages, FUSE_MAX_PAGES_PER_REQ);
>  
>  	err = -EIO;
>  	if (is_bad_inode(inode))
> @@ -683,7 +688,8 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
>  
>  	data.file = file;
>  	data.inode = inode;
> -	data.req = fuse_get_req_multipage(fc, FUSE_MAX_PAGES_PER_REQ);
> +	data.req = fuse_get_req_multipage(fc, nr_alloc);
> +	data.nr_pages = nr_pages;
>  	err = PTR_ERR(data.req);
>  	if (IS_ERR(data.req))
>  		goto out;