Re: [PATCH] recognize MAP_LOCKED in mmap() call

[Andrew Morton <akpm@digeo.com>]

Hubertus Franke wrote:
> 
> ...
> This is what the manpage says...
> 
>        mlockall  disables  paging  for  all pages mapped into the
>        address space of the calling process.  This  includes  the
>        pages  of  the  code,  data  and stack segment, as well as
>        shared libraries, user space kernel  data,  shared  memory
>        and  memory  mapped files. All mapped pages are guaranteed
>        to be resident  in  RAM  when  the  mlockall  system  call
>        returns  successfully  and  they are guaranteed to stay in
>        RAM until the pages  are  unlocked  again  by  munlock  or
>        munlockall  or  until  the  process  terminates  or starts
>        another program with exec.  Child processes do not inherit
>        page locks across a fork.
> 
> Do you read that all pages must be faulted in apriori ?

For MCL_FUTURE.

> Or is it sufficient to to make sure non of the currently mapped
> pages are swapped out and future swapout is prohibited.

I'd say that we should try to make all the pages present.  But
if it's a problem for (say) a hugepage implementation then it's
unlikely that the world would end if these things were still
demand paged in.