From: Konstantin Khorenko <khorenko@xxxxxxxxxxxxx> Date: Fri, 10 Aug 2018 20:11:41 +0300 > Each SCTP association can have up to 65535 input and output streams. > For each stream type an array of sctp_stream_in or sctp_stream_out > structures is allocated using kmalloc_array() function. This function > allocates physically contiguous memory regions, so this can lead > to allocation of memory regions of very high order, i.e.: > > sizeof(struct sctp_stream_out) == 24, > ((65535 * 24) / 4096) == 383 memory pages (4096 byte per page), > which means 9th memory order. > > This can lead to a memory allocation failures on the systems > under a memory stress. > > We actually do not need these arrays of memory to be physically > contiguous. Possible simple solution would be to use kvmalloc() > instread of kmalloc() as kvmalloc() can allocate physically scattered > pages if contiguous pages are not available. But the problem > is that the allocation can happed in a softirq context with > GFP_ATOMIC flag set, and kvmalloc() cannot be used in this scenario. > > So the other possible solution is to use flexible arrays instead of > contiguios arrays of memory so that the memory would be allocated > on a per-page basis. > > This patchset replaces kvmalloc() with flex_array usage. > It consists of two parts: > > * First patch is preparatory - it mechanically wraps all direct > access to assoc->stream.out[] and assoc->stream.in[] arrays > with SCTP_SO() and SCTP_SI() wrappers so that later a direct > array access could be easily changed to an access to a > flex_array (or any other possible alternative). > * Second patch replaces kmalloc_array() with flex_array usage. Looks good, series applied, thanks!
