On 7/11/24 15:55, Edgecombe, Rick P wrote: >> Where current is a 'task_struct' which is in /proc/slabinfo and 'struct >> thread_struct thread' and 'struct fpu' are embedded in 'task_struct', >> not allocated on their own: > I think thread_struct is always a slab, but the current->thread.fpu.fpstate > pointer can be reallocated to point to a vmalloc in fpstate_realloc(), in the > case of XFD features. Good point. I was ignoring XFD and AMX. They're super rare and (conditionally) add another 8k. -- Well, closer to 11k since we duplicate some of the XSAVE area. -- But honestly, even if the AMX 'struct fpu' fit perfectly into 4k*3 pages and CET-S made it take 4k*4 pages, I'm not sure I'd even care. It would only affect AMX-using apps on AMX-capable hardware. So a small minority of tasks on a small minority of one x86 vendor's CPUs. The (potential) space consumption from the inline task_struct fpu will matter a lot more across all Linux users than AMX ever will. It would affect all tasks on all CPUs that have CET-S which will hopefully be the majority of x86 CPUs running Linux some day.
