Mailinglist Archive: opensuse (1239 mails)

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Re: [opensuse] Re: XFS and openSUSE 12.1
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Fri, 14 Jun 2013 07:32:18 +0200
  • Message-id: <1371187938.2700.10.camel@acme.pacific>
On Thu, 2013-06-13 at 21:09 +0200, Carlos E. R. wrote:
On 2013-06-13 18:03, Roger Oberholtzer wrote:
On Thu, 2013-06-13 at 10:18 -0400, Greg Freemyer wrote:

fyi: This is a new call to me and I've never used it, so I have no
first hand feedback.

Initial tests look promising. When the call is done, the cache drops by
whatever the app has caused to be added. Unlike the brute-force approach
I first did, the cache for other activities is not effected.

Let me clarify.

The cache initially grows while calls are made, and when the file is
closed, it drops. About to gigs, right? Well that's very good, just what
you need.

It does not drop when the file is closed. Only if the file is deleted or
the file system umounted (neither of which I can reasonably do IRL), or
posix_fadvise(fp, 0, 0, POSIX_FADV_DONTNEED) is called. So I now call
posix_fadvise() periodically. I do not fiddle with fdatasync as I do not
mind a reasonable bit if buffering.

If the cache was really mainly a read cache and not tons of stuff
waiting to do to disk (as seems to be implied in various discussions),
then I do not understand the occasional >4 second fwrite() delays and,
more importantly, why the call to posix_fadvise() helps. That call does
not cause a flush. It only arranges that pages that do not contain
unique information (in mem and not on disk) are freed. Perhaps I am not
meant to understand this mystery :)

I am satisfied that I have a solution. I am still not satisfied that the
dynamics of the situation are what we think. But life must go on. And
testing proceed.

Yours sincerely,

Roger Oberholtzer

Ramböll RST / Systems

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

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