On Thu 30-11-17 10:31:12, John Hubbard wrote: > On 11/30/2017 12:24 AM, Michal Hocko wrote: > > Updated version based on feedback from John. > > --- > > From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <mhocko@xxxxxxxx> > > Date: Wed, 29 Nov 2017 15:32:08 +0100 > > Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag > > > > 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to > > atomicaly probe for a given address range. > > > > [wording heavily updated by John Hubbard <jhubbard@xxxxxxxxxx>] > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > > --- > > man2/mmap.2 | 22 ++++++++++++++++++++++ > > 1 file changed, 22 insertions(+) > > > > diff --git a/man2/mmap.2 b/man2/mmap.2 > > index 385f3bfd5393..923bbb290875 100644 > > --- a/man2/mmap.2 > > +++ b/man2/mmap.2 > > @@ -225,6 +225,22 @@ will fail. > > Because requiring a fixed address for a mapping is less portable, > > the use of this option is discouraged. > > .TP > > +.BR MAP_FIXED_SAFE " (since Linux 4.16)" > > +Similar to MAP_FIXED with respect to the > > +.I > > +addr > > +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing > > +mapped range. If the requested range would collide with an existing > > +mapping, then this call fails with > > +.B EEXIST. > > +This flag can therefore be used as a way to atomically (with respect to other > > +threads) attempt to map an address range: one thread will succeed; all others > > +will report failure. Please note that older kernels which do not recognize this > > +flag will typically (upon detecting a collision with a pre-existing mapping) > > +fall back a "non-MAP_FIXED" type of behavior: they will return an address that > > ...and now I've created my own typo: please make that "fall back to a" (the > "to" was missing). > > Sorry about the churn. It turns out that the compiler doesn't catch these. :) Fixed. I will resubmit after there is more feedback review. Thanks -- Michal Hocko SUSE Labs
