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@xxxxxxxxx>
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
Reviewed-by: Dmitry Safonov <0x7f454c46@xxxxxxxxx>
> ---
> 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
