Re: cache limit

[Andrew Morton]

Denis Vlasenko <vda@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> There was a discussion (and patches) in the middle of 2.5 series
>  about O_STREAMING open flag which mean "do not aggressively cache
>  this file". Targeted at MP3/video playing, copying large files and such.
> 
>  I don't know whether it actually was merged. If it was,
>  your program can use it.

It was not.  Instead we have fadvise.  So it would be appropriate to change
applications such as rsync to optionally run

	posix_fadvise(fd, 0, -1, POSIX_FADV_DONTNEED)

against file descriptors just before closing them, so all the pagecache
gets thrown away.  (Well, most of the pagecache - dirty pages won't get
dropped - the app must fsync the files by hand first if it wants this)

This would be a useful addition to rsync and such applications - it is
stronger and more specific and safer than banging on the VM for a special
case.

But if you want to bang on the VM for a special case, run 2.6 and set
/proc/sys/vm/swappiness to zero during the rsync run.

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