Re: [PATCH v3][RFC] add MAP_UNLOCKED mmap flag

[WANG Cong <xiyou.wangcong@gmail.com>]

Gleb Natapov <gleb@redhat.com> writes:

> If application does mlockall(MCL_FUTURE) it is no longer possible to
> mmap file bigger than main memory or allocate big area of anonymous
> memory. Sometimes it is desirable to lock everything related to program
> execution into memory, but still be able to mmap big file or allocate
> huge amount of memory and allow OS to swap them on demand. MAP_UNLOCKED
> allows to do that.
>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>

<snip>

> diff --git a/mm/mmap.c b/mm/mmap.c
> index 73f5e4b..ecc4471 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -985,6 +985,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
>  		if (!can_do_mlock())
>  			return -EPERM;
>  
> +        if (flags & MAP_UNLOCKED)
> +                vm_flags &= ~VM_LOCKED;
> +
>  	/* mlock MCL_FUTURE? */
>  	if (vm_flags & VM_LOCKED) {
>  		unsigned long locked, lock_limit;

So, if I read it correctly, it is perfectly legal to set
both MAP_LOCKED and MAP_UNLOCKED at the same time? While
the behavior is still same as only setting MAP_UNLOCKED.

Is this what we expect?

Regards.

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