Messages in this thread Patch in this message | | | Date | Wed, 5 Jan 2022 06:54:20 +0000 | Subject | Re: [PATCH] fs/pipe: use kvcalloc to allocate a pipe_buffer array | From | Dmitry Safonov <> |
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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@gmail.com> > Signed-off-by: Andrei Vagin <avagin@gmail.com>
Good idea!
I wonder if you need to apply this on the top:
diff --git a/fs/pipe.c b/fs/pipe.c index 45565773ec33..b4ccafffa350 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -605,7 +605,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct pipe_inode_info *pipe = filp->private_data; - int count, head, tail, mask; + unsigned int count, head, tail, mask;
switch (cmd) { case FIONREAD: @@ -827,7 +827,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
void free_pipe_info(struct pipe_inode_info *pipe) { - int i; + unsigned int i;
#ifdef CONFIG_WATCH_QUEUE if (pipe->watch_queue) { --->8--- Otherwise this loop in free_pipe_info() may become lockup on some ugly platforms with INTMAX allocation reachable, I think. I may be wrong :-)
Thanks, Dmitry
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