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Re: [FAQ] XFS speculative preallocation

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [FAQ] XFS speculative preallocation
From: Florian Weimer <fw@xxxxxxxxxxxxx>
Date: Fri, 21 Mar 2014 21:11:29 +0100
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140321162920.GA3087@xxxxxxxxxxxxxx> (Brian Foster's message of "Fri, 21 Mar 2014 12:29:20 -0400")
References: <20140321162920.GA3087@xxxxxxxxxxxxxx>
* Brian Foster:

> Although speculative preallocation can lead to reports of excess space
> usage, the preallocated space is not permanent unless explicitly made so
> via fallocate or a similar interface.

How does an explicit allocation with posix_fallocate interact with
speculative preallocation?  Does it disable it?

I see rather dramatic fragmentation of the systemd journal when it is
stored on XFS, and it calls posix_fallocate before writing data to the

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