On Thu, 24 Feb 2000, Stephen C. Tweedie wrote:
> Hi,
>
> 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.
Ah, this is cool - exactly what we need. I.e. an madvise(MADV_DONTNEED)
and a subsequent munmap should not generate any disk io?
> Regarding the other half of the problem --- zeroing out a portion of a
> file without further IO --- the splice code I hope to have using kiobufs
> in 2.5 will allow this to be done very easily. You'll be able to take a
> region of /dev/zero and splice it into your open file with zero-copy.
Cool, too. So for now we will stay with zeroing by reading from /dev/zero
which does vm tricks in linux already.
Richard.
> --Stephen
>
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This archive was generated by hypermail 2b29 : Tue Feb 29 2000 - 21:00:09 EST