Re: Patch nag: Bug #363400

[Alexander Larsson <alexl redhat com>]

On Mon, 2007-03-26 at 12:31 -0600, Hans Petter Jansson wrote:
> On Mon, 2007-03-26 at 10:50 +0200, Alexander Larsson wrote:
> > On Wed, 2007-03-21 at 14:28 -0600, Hans Petter Jansson wrote:
> 
> > > http://bugzilla.gnome.org/show_bug.cgi?id=363400
> > > 
> > > Has a gnome-vfs patch that I believe to be correct. It works around a
> > > serious performance issue on XFS file systems. It has been tested by at
> > > least two users.
> 
> > That patch removes the size limit for when using fadvice. I don't think
> > this is right. For small files we don't want to flush them from the
> > cache, as that could cause performance issues (we might be copying a
> > commonly used file).
> 
> No. The following condition:
> 
> if (bytes_to_write == 0 &&
>     total_bytes_read - last_cache_drop_point >= DROP_CACHE_BATCH_SIZE)
> 
> Will trigger for the first time once DROP_CACHE_BATCH_SIZE has been
> reached. fadvise() will be triggered at the end of each batch, not at
> the beginning.

But DROP_CACHE_BATCH_SIZE is far smaller (512k) than
DROP_CACHE_SIZE_LIMIT (20 meg). Now, i didn't do much scientific
research to get to the DROP_CACHE_SIZE_LIMIT value, but its a large
change that might cause regressions (or be better, who really knows...)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Alexander Larsson                                            Red Hat, Inc 
                   alexl redhat com    alla lysator liu se 
He's a hate-fuelled playboy dwarf haunted by an iconic dead American 
confidante She's a psychotic tempestuous vampire from a different time and 
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