[PATCH 0/1] LP#444915: readahead not merging in the elevator

Colin Ian King colin.king at canonical.com
Tue Oct 13 12:24:09 UTC 2009

On Tue, 2009-10-13 at 12:18 +0100, Andy Whitcroft wrote:
> We have reports of slow mounting of FAT filesystems on external drives.
> This turns out to be a bug in the new fastfail code in the elevator which
> completely prevents merging of any readahead requests.  As all of the
> FAT reads are pre-readahead to fix this very performance problem they
> all were submitted to the device as single 512 transactions.  Fail.
> This patch implements the painfully obvious fix for the issue.
> Thanks to Stefan Bader for keeping me sane during the extended debug.
> For Karmic.
> -apw
> Andy Whitcroft (1):
>   UBUNTU: [Upstream] elevator: fix fastfail checks to allow merge of
>     readahead requests
>  block/elevator.c |   14 ++++++++++----
>  1 files changed, 10 insertions(+), 4 deletions(-)
With your explanation, it is an "obvious" fix, (without the explanation
it would require even deeper thought :-)


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