K 10
svn:author
V 5
markj
K 8
svn:date
V 27
2020-06-25T20:30:30.676879Z
K 7
svn:log
V 960
Implement an approximation of Linux MADV_DONTNEED semantics.

Linux MADV_DONTNEED is not advisory: it has side effects for anonymous
memory, and some system software depends on that.  In particular,
MADV_DONTNEED causes anonymous pages to be discarded.  If the mapping is
a private mapping of a named object then subsequent faults are to
repopulate the range from that object, otherwise pages will be
zero-filled.  For mappings of non-anonymous objects, Linux MADV_DONTNEED
can be implemented in the same way as our MADV_DONTNEED.

This implementation differs from Linux semantics in its handling of
private mappings, inherited through fork(), of non-anonymous objects.
After applying MADV_DONTNEED, subsequent faults will repopulate the
mapping from the parent object rather than the root of the shadow chain.

PR:		230160
Reviewed by:	alc, kib
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D25330

END