linux-kernel - Re: [PATCH] fs/pipe: use kvcalloc to allocate a pipe

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Message-ID: <cbe26979-15cd-a460-7f9d-6035f8862073@gmail.com>
Date:   Thu, 6 Jan 2022 17:37:03 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Andrei Vagin <avagin@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] fs/pipe: use kvcalloc to allocate a pipe_buffer array

On 1/4/22 17:10, Andrei Vagin wrote:
> Right now, kcalloc is used to allocate a pipe_buffer array.  The size of
> the pipe_buffer struct is 40 bytes. kcalloc allows allocating reliably
> chunks with sizes less or equal to PAGE_ALLOC_COSTLY_ORDER (3). It means
> that the maximum pipe size is 3.2MB in this case.
> 
> In CRIU, we use pipes to dump processes memory. CRIU freezes a target
> process, injects a parasite code into it and then this code splices
> memory into pipes. If a maximum pipe size is small, we need to
> do many iterations or create many pipes.
> 
> kvcalloc attempt to allocate physically contiguous memory, but upon
> failure, fall back to non-contiguous (vmalloc) allocation and so it
> isn't limited by PAGE_ALLOC_COSTLY_ORDER.
> 
> The maximum pipe size for non-root users is limited by
> the /proc/sys/fs/pipe-max-size sysctl that is 1MB by default, so only
> the root user will be able to trigger vmalloc allocations.
> 
> Cc: Dmitry Safonov <0x7f454c46@...il.com>
> Signed-off-by: Andrei Vagin <avagin@...il.com>

Reviewed-by: Dmitry Safonov <0x7f454c46@...il.com>


> ---
>  fs/pipe.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 6d4342bad9f1..45565773ec33 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -802,7 +802,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
>  	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
>  		goto out_revert_acct;
>  
> -	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
> +	pipe->bufs = kvcalloc(pipe_bufs, sizeof(struct pipe_buffer),
>  			     GFP_KERNEL_ACCOUNT);
>  
>  	if (pipe->bufs) {
> @@ -845,7 +845,7 @@ void free_pipe_info(struct pipe_inode_info *pipe)
>  	}
>  	if (pipe->tmp_page)
>  		__free_page(pipe->tmp_page);
> -	kfree(pipe->bufs);
> +	kvfree(pipe->bufs);
>  	kfree(pipe);
>  }
>  
> @@ -1260,8 +1260,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
>  	if (nr_slots < n)
>  		return -EBUSY;
>  
> -	bufs = kcalloc(nr_slots, sizeof(*bufs),
> -		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
> +	bufs = kvcalloc(nr_slots, sizeof(*bufs), GFP_KERNEL_ACCOUNT);
>  	if (unlikely(!bufs))
>  		return -ENOMEM;
>  
> @@ -1288,7 +1287,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
>  	head = n;
>  	tail = 0;
>  
> -	kfree(pipe->bufs);
> +	kvfree(pipe->bufs);
>  	pipe->bufs = bufs;
>  	pipe->ring_size = nr_slots;
>  	if (pipe->max_usage > nr_slots)


Thanks,
          Dmitry