Re: [RFC 1/2] deactive invalidated pages

[Ben Gamari]

On Tue, 23 Nov 2010 16:16:55 +0900 (JST), KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> > By Other approach, app developer uses POSIX_FADV_DONTNEED.
> > But it has a problem. If kernel meets page is writing
> > during invalidate_mapping_pages, it can't work.
> > It is very hard for application programmer to use it.
> > Because they always have to sync data before calling
> > fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could
> > be discardable. At last, they can't use deferred write of kernel
> > so that they could see performance loss.
> > (http://insights.oetiker.ch/linux/fadvise.html)
> 
> If rsync use the above url patch, we don't need your patch. 
> fdatasync() + POSIX_FADV_DONTNEED should work fine.
> 
This is quite true, but the patch itself is fairly invasive and
unnecessarily so which makes it unsuitable for merging in the eyes of
the rsync maintainers (not that I can blame them). This is by no fault
of its author; using fadvise is just far harder than it should be.

- Ben
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