Mailinglist Archive: opensuse (1239 mails)

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Re: [opensuse] Re: XFS and openSUSE 12.1
Carlos E. R. wrote:
On 2013-06-13 08:02, Roger Oberholtzer wrote:
On Thu, 2013-06-13 at 06:24 +0200, Carlos E. R. wrote:
Linda idea of using "posix_fadvise" and opening the file for
write only seems to me a very good one. But she also said "the
calls are advisory".
posix_fadvise(POSIX_FADV_DONTNEED) seems not to be advisory. It
clears info for the specified file from the cache when it is
called. So it needs to do this regularly. Which is no problem. I
just need to figure out the 'start' and 'stop' parameters.

That it works does not deny being advisory :-)

Maybe it means that it has been implemented and works.

Exactly. Remember that this is a POSIX call. There are many other
operating systems than Linux that accept this call. Some of them may not
follow the instruction it provides. Hence it is advisory. It is not a
requirement on an operating system to obey this instruction in order to
conform to POSIX. But apparently Linux does, at least in these
circumstances.

By the way, try not to use "fsync". It forces the kernel to write to
disk even if not convenient.

I think this is misguided advice. It is very important to use use fsync
to ensure that the data makes it onto the disk in order to ensure data
or whole files don't disappear. On a rename for example, it is necessary
to fsync the directory as well as the file. The point is that
application correctness is more important than kernel or filesystem
convenience. But clearly, fsync checkpoints should be chosen wisely, on
transaction boundaries, perhaps, not on every write.
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