[Bug 240061] MADV_FREE rewinds time to before fork()
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Wed Sep 4 20:28:34 UTC 2019
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240061
--- Comment #7 from commit-hook at freebsd.org ---
A commit references this bug:
Author: kib
Date: Wed Sep 4 20:28:16 UTC 2019
New revision: 351830
URL: https://svnweb.freebsd.org/changeset/base/351830
Log:
madvise(MADV_FREE): Quick fix to time rewind.
Don't free pages in a shadowing object. While this degrades MADV_FREE
to a no-op (and we could, instead, choose to fall back to
MADV_DONTNEED, at the cost of changing pmap_madvise), this is
presently considered a temporary fix. We may prefer to risk a little
fragmentation of the map by creating a zero/OBJT_DEFAULT entry over
top of the existing object and, simultaneously, revert to the existing
marking any pages in the former shadowing object in the advised region
as reclaimable. At least one consumer of MADV_FREE (snmalloc) may use
mmap() to construct zeroed pages "eventually" here anyway, so the
fragmentation may be coming anyway.
Submitted by: Nathaniel Filardo <nwf20 at cl.cam.ac.uk>
PR: 240061
Reviewed by: markj
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D21517
Changes:
head/sys/vm/vm_map.c
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