[Bug 7876] please implement o_direct

[samba-bugs at samba.org]

https://bugzilla.samba.org/show_bug.cgi?id=7876

--- Comment #6 from costin gusa <costinel at gmail.com> 2011-04-30 12:55:16 UTC ---
(In reply to comment #4)
> Thanks for your feedback!
> 
> I had just found the patch by Tobi myself, and it is using mincore (now) to
> check if a file has been cached before rsync touched it (and then skip removing
> it from the cache).
> 
> Post: http://insights.oetiker.ch/linux/fadvise.html
> Patch for 3.0.7: http://tobi.oetiker.ch/patches/rsync-3.0.7-fadvise.patch
> 
> I agree that something like "nice" and "ionice" would be the best approach, and
> I find it rather unusual to not have something like that available already.
> I have found the following wrapper, which is using O_DIRECT however:
> http://arighi.blogspot.com/2007/04/how-to-bypass-buffer-cache-in-linux.html
> 
> For what it's worth, here's a link to the POSIX_FADV_DONTNEED implementation in
> the current kernel:
> http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.37.y.git;a=blob;f=mm/fadvise.c;hb=refs/heads/master#l118

To me as an end user is irrelevant what method is chosen to avoid filling up
the cache.

The LD_PRELOAD library wrapper solution looks like a more logic approach;
however besides the mentioned blogspot article, are there out successful usage
reports based on it?

Second, if the answer to the previous question is "yes", how can I enable it
remotely ? - My backup solution is a "pull" type - to avoid a bunch of servers
potentially abuse the backup machine, only the backup machine connects to
servers. So if I on the backup machine would be able to run rsync with
LD_PRELOAD wrapper, how do I run the remote '-e ssh' rsync with the LD_PRELOAD
wrapper?

Thank you.

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