Jörn Engel wrote:
On Tue, 28 June 2005 16:05:11 -0400, Robert Love wrote:
I like the idea (I think someone suggested this early on) of renaming
the current MADV_DONTNEED to MADV_FREE and then adding a correct
MADV_DONTNEED.
Imo, that's still a crime against common sense. Madvice should give
the kernel some advice about which data to keep or not to keep in
memory, hence the name. It should *not* tell the kernel to corrupt
data, which currently appears to be the case.
If the application knows 100% that it is the _only_ possible user of
this data and will never again use it, dropping dirty pages might be a
sane option. Effectively that translates to anonymous memory only.
In all other cases, dirty pages should be written back.
There is also the case of shmget/shmat memory segments. Some
applications will use these in order to map a very large amount of
memory and then madvise(MADV_DONTNEED) in order to play nice with the
rest of the system should memory pressure / system load / etc require
it. Obviously if other tasks have these segments mapped, the pages
cannot be discarded. If a task is the sole "mapper" of the region and
doesn't need that memory (ever again) it would be good to avoid the i/o
overhead of swapping it out and just discarding it. Perhaps
MADV_DONTNEED isn't the right place for this, but there is demand for
this behavior.
--Darren Hart
And, as I said, the man page needs clarification.
Definitely.
Jörn
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