Re: [PATCH v2 1/2] fs/pipe: pre-allocate pages outside pipe->mutex in anon_pipe_write

[Oleg Nesterov <oleg@redhat.com>]

To be honest, I didn't read this patch carefully, but let me ask anyway.

On 05/22, Breno Leitao wrote:
>
> @@ -432,6 +524,7 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
>  {
>  	struct file *filp = iocb->ki_filp;
>  	struct pipe_inode_info *pipe = filp->private_data;
> +	struct anon_pipe_prealloc prealloc;
>  	unsigned int head;
>  	ssize_t ret = 0;
>  	size_t total_len = iov_iter_count(from);
> @@ -455,6 +548,8 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
>  	if (unlikely(total_len == 0))
>  		return 0;
>  
> +	anon_pipe_get_page_prealloc(&prealloc, total_len);
> +
>  	mutex_lock(&pipe->mutex);
>  
>  	if (!pipe->readers) {
> @@ -512,7 +607,7 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
>  			struct page *page;
>  			int copied;
>  
> -			page = anon_pipe_get_page(pipe);
> +			page = anon_pipe_get_page(pipe, &prealloc);
>  			if (unlikely(!page)) {
>  				if (!ret)
>  					ret = -ENOMEM;
> @@ -566,7 +661,9 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
>  		 * after waiting we need to re-check whether the pipe
>  		 * become empty while we dropped the lock.
>  		 */
> +		anon_pipe_refill_tmp_pages(pipe, &prealloc);
>  		mutex_unlock(&pipe->mutex);
> +		anon_pipe_free_pages(&prealloc);

Do we really want to call anon_pipe_free_pages() at this point?

The main loop will continue when pipe_writable() becomes true again...

Oleg.