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Re: [PATCH v2] xfs: increase prealloc size to double that of the previou

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH v2] xfs: increase prealloc size to double that of the previous extent
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 7 Mar 2013 12:45:04 -0600
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1361287481-9649-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1361287481-9649-1-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue, Feb 19, 2013 at 10:24:41AM -0500, Brian Foster wrote:
> The updated speculative preallocation algorithm for handling sparse
> files can becomes less effective in situations with a high number of
> concurrent, sequential writers. The number of writers and amount of
> available RAM affect the writeback bandwidth slicing algorithm,
> which in turn affects the block allocation pattern of XFS. For
> example, running 32 sequential writers on a system with 32GB RAM,
> preallocs become fixed at a value of around 128MB (instead of
> steadily increasing to the 8GB maximum as sequential writes
> proceed).
> 
> Update the speculative prealloc heuristic to base the size of the
> next prealloc on double the size of the preceding extent. This
> preserves the original aggressive speculative preallocation
> behavior and continues to accomodate sparse files at a slight cost
> of increasing the size of preallocated data regions following holes
> of sparse files.
> 
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>

Excuse me.  This is the version I applied.  Not v1.

-Ben

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