On Tue 19-12-17 12:40:16, David Laight wrote:

From: Edward Napierala

quoted

Sent: 14 December 2017 14:55

On 1214T1415, Michal Hocko wrote:

quoted

On Thu 14-12-17 12:44:17, Edward Napierala wrote:

quoted

Regarding the name - how about adopting MAP_EXCL?  It was introduced in
FreeBSD,
and seems to do exactly this; quoting mmap(2):

MAP_FIXED    Do not permit the system to select a different address
                        than the one specified.  If the specified address
                        cannot be used, mmap() will fail.  If MAP_FIXED is
                        specified, addr must be a multiple of the page size.
                        If MAP_EXCL is not specified, a successful MAP_FIXED
                        request replaces any previous mappings for the
                        process' pages in the range from addr to addr + len.
                        In contrast, if MAP_EXCL is specified, the request
                        will fail if a mapping already exists within the
                        range.

I am not familiar with the FreeBSD implementation but from the above it
looks like MAP_EXCL is a MAP_FIXED mofifier which is not how we are
going to implement it in linux due to reasons mentioned in this cover
letter. Using the same name would be more confusing than helpful I am
afraid.

Sorry, missed that.  Indeed, reusing a name with a different semantics
would be a bad idea.

I don't remember any discussion about using MAP_FIXED | MAP_EXCL ?

Why not match the prior art??

See the cover letter which explains why an extension is not backward
compatible.
-- 
Michal Hocko
SUSE Labs

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