Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: fadvise DONTNEED implementation (or lack thereof) | Date | Tue, 9 Nov 2010 17:03:09 +0900 (JST) |
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> > I've recently been trying to track down the root cause of my server's > > persistent issue of thrashing horribly after being left inactive. It > > seems that the issue is likely my nightly backup schedule (using rsync) > > which traverses my entire 50GB home directory. I was surprised to find > > that rsync does not use fadvise to notify the kernel of its use-once > > data usage pattern. > > > > It looks like a patch[1] was written (although never merged, it seems) > > incorporating fadvise support, but I found its implementation rather > > odd, using mincore() and FADV_DONTNEED to kick out only regions brought > > in by rsync. It seemed to me the simpler and more appropriate solution > > would be to simply flag every touched file with FADV_NOREUSE and let the > > kernel manage automatically expelling used pages. > > > > After looking deeper into the kernel implementation[2] of fadvise() the > > reason for using DONTNEED became more apparant. It seems that the kernel > > implements NOREUSE as a noop. A little googling revealed[3] that I not > > the first person to encounter this limitation. It looks like a few > > folks[4] have discussed addressing the issue in the past, but nothing > > has happened as of 2.6.36. Are there plans to implement this > > functionality in the near future? It seems like the utility of fadvise > > is severely limited by lacking support for NOREUSE. > > btw, Other OSs seems to also don't implement it. > example,
I've heared other OSs status of fadvise() from private mail.
NetBSD: no-op (as linux) FreeBSD/DragonflyBSD/OpenBSD: don't exist posix_fadvise(2)
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