Date: Tue, 03 Sep 2019 15:01:33 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 240061] MADV_FREE rewinds time to before fork() Message-ID: <bug-240061-227-RHV8r9O8Tp@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-240061-227@https.bugs.freebsd.org/bugzilla/> References: <bug-240061-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240061 --- Comment #6 from Mark Johnston <markj@FreeBSD.org> --- One possible alternative is to convert MADV_FREE to MADV_DONTNEED if the object has a backing object. pmap_advise() needs to be updated to preserve the modified bits, but this should be fine since vm_page_advise(MADV_FREE) calls vm_page_undirty() anyway. Some basic testing on my workstation showed that virtually all calls to vm_object_madvise(MADV_FREE) are acting on an object with no backing object. Obviously this may not be true in general. # dtrace -n 'fbt::vm_object_madvise:entry /args[0] && args[3] == 5/{@[args[0]->backing_object == NULL] = count();}' ^C 0 13 1 17504 Untested patch here: https://people.freebsd.org/~markj/patches/madvise_cow.diff -- You are receiving this mail because: You are the assignee for the bug.help
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