lkml.org 
[lkml]   [2005]   [Mar]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] use cheaper elv_queue_empty when unplug a device
Arjan van de Ven wrote:
> On Tue, 2005-03-29 at 19:19 +1000, Nick Piggin wrote:
>
>>- removes the relock/retry merge mechanism in __make_request if we
>> aren't able to get the GFP_ATOMIC allocation. Just fall through
>> and assume the chances of getting a merge will be small (is this
>> a valid assumption? Should measure it I guess).
>
>
> this may have a potential problem; if the vm gets in trouble, you
> suddenly start to generate worse IO patterns, which means IO performance
> goes down right when it's most needed.....
>

Sorry my wording was incorrect. It currently *always* retries the
merge if it had at first failed, and after the patch, we never retry.
So it should not result in behavioural shifts when there is a VM load
is high.

It seems to be a clear source of problems for Kenneth though, because
his workload appears to have almost zero merges, so he'll always be
invoking the merge logic twice.

I agree there is potential for subtle interactions. But generally the
block layer is surprisingly well behaved in my experience.

As Jens said, the complete removal of the GFP_ATOMIC allocation probably
has the most potential for problems in this regard, although bios are not
using GFP_ATOMIC allocations, so I would be a little surprised if it made
a really noticable difference.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-04-06 13:31    [W:0.100 / U:5.440 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site