On Tue, Jan 4, 2022 at 9:11 AM Andrei Vagin <avagin@xxxxxxxxx> 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> Alexander and Andrew, Do you have any objections? Could you merge this patch? Dmitry's comments have been addressed in the separate patch: https://lkml.org/lkml/2022/1/6/463 BTW: I found that fuse already uses kvmalloc to allocate pipe buffers (e. g. fuse_dev_splice_read). Thanks, Andrei
