Messages in this thread | | | Date | Thu, 24 Feb 2000 14:06:08 +0100 | From | lars brinkhoff <> | Subject | Re: mmap/munmap semantics |
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"Stephen C. Tweedie" wrote: > On Thu, 24 Feb 2000 03:35:02 +0100, Jamie Lokier > <lk@tantalophile.demon.co.uk> said: > > I don't think MADV_DONTNEED actually drops privately modified data does > > it? > Yes, it does. From the DU man pages: > > MADV_DONTNEED > Do not need these pages > > The system will free any whole pages in the specified > region. All modifications will be lost and any swapped > out pages will be discarded. Subsequent access to the > region will result in a zero-fill-on-demand fault as > though it is being accessed for the first time. > Reserved swap space is not affected by this call.
From a FreeBSD man page at http://dorifer.heim3.tu-clausthal.de/cgi-bin/man/madvise.2.html
MADV_DONTNEED Allows the VM system to decrease the in-memory priority of pages in the specified range. Additionally future references to this address range will incur a page fault.
MADV_FREE Gives the VM system the freedom to free pages, and tells the system that information in the specified page range is no longer important. This is an efficient way of al- lowing malloc(3) to free pages anywhere in the address space, while keeping the address space valid. The next time that the page is referenced, the page might be de- mand zeroed, or might contain the data that was there before the MADV_FREE call. References made to that ad- dress space range will not make the VM system page the information back in from backing store until the page is modified again.
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