[FreeVMS] pager question

[BERTRAND Joël]

Guido a écrit :
> On Saturday 29 June 2013 12:44:23 BERTRAND Joël wrote:
>> 	I agree. For kernel itself, sys_pagefault always returns new
>> ressources. For an unprivilegied process, pager has to save a list of
>> allocated pages for this process. Pagefault handler only has to return
>> new pages when process is loaded in memory, when stack is growing or
>> when process uses something like mmap() or brk(). In all other cases,
>> pagefault has to raise a new syscall to kill process.
>
> OK, but could you explain why a page fault (essentially a hardware generated
> error condition) and a memory allocation request (software generated, on
> purpose) are handled by the same function (the pagefault handler) when they
> are to be handled differently? Wouldn't it be easier to have separate IPC calls
> and handlers?

	When a process try to access to a unmapped page, it generates a 
pagefault IPC. This IPC is received by an event handler loop in its 
parent (for example, PAGER.SYS sends L4_PAGEFAULT IPC to VMSKERNEL.SYS 
and all IPC are caught in sys/sys_loop.c).

	Child process does not know if its request can or will be done. It only 
sends L4_PAGEFAULT IPC to its parent and waits for an answer. This 
answer can be a new L4_MapItem() or a L4_AbortIpc_and_stop(). Thus, I 
don't see why we need to separate L4_PAGEFAULT IPC in two IPC calls.

	Regards,

	JKB