On Thu, 2016-09-22 at 18:56 +0200, Vlastimil Babka wrote: > On 09/22/2016 06:49 PM, Eric Dumazet wrote: > > On Thu, 2016-09-22 at 18:43 +0200, Vlastimil Babka wrote: > >> The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows > >> with the number of fds passed. We had a customer report page allocation > >> failures of order-4 for this allocation. This is a costly order, so it might > >> easily fail, as the VM expects such allocation to have a lower-order fallback. > >> > >> Such trivial fallback is vmalloc(), as the memory doesn't have to be > >> physically contiguous. Also the allocation is temporary for the duration of the > >> syscall, so it's unlikely to stress vmalloc too much. > > > > vmalloc() uses a vmap_area_lock spinlock, and TLB flushes. > > > > So I guess allowing vmalloc() being called from an innocent application > > doing a select() might be dangerous, especially if this select() happens > > thousands of time per second. > > Isn't seq_buf_alloc() similarly exposed? And ipc_alloc()? Possibly. We don't have a library function (attempting kmalloc(), fallback to vmalloc() presumably to avoid abuses, but I guess some patches were accepted without thinking about this. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>