Re: [dm-devel] scsi_dh_rdac: Changing the memory allocation flag from GFP_KERNEL to GFP_NOIO

[Mike Snitzer <snitzer redhat com>]

This patch appears to have gotten lost in the shuffle but still seems
relevant.  I found it while auditing dm-devel's patchwork, patch is
here: https://patchwork.kernel.org/patch/71073/

On Tue, Jan 05 2010 at 12:20pm -0500,
Moger, Babu <Babu Moger lsi com> wrote:

> This patch changes the memory allocation flag from GFP_KERNEL to GFP_NOIO which is more appropriate.
> 
> This was noticed by Mike Christie and Rob Evers.. 
> Mike Christie wrote:
> > Rob Evers wrote:
> >> +
> >> +static int queue_mode_select(struct scsi_device *sdev,
> >> +                activate_complete fn, void *data)
> >> +{
> >> +    struct rdac_queue_data *qdata;
> >> +    struct rdac_controller *ctlr;
> >> +
> >> +    qdata = kzalloc(sizeof(*qdata), GFP_KERNEL);
> >> +    if (!qdata)
> >> +        return SCSI_DH_RETRY;
> >> +
> >
> > It looks like this is called in the main IO path. A failed IO could cause, the path to go down,
> > then we would call this to active a new path. If the system needed to write out pages to the same
> > disk that just had the failed path so it can allocate memory then GFP_KERNEL would be bad to use here.
> > You would use a mempool and still use something like GFP_NOIO. If a mempool is not possible for some 
> > reason, then you would want to still use GFP_NOIO.
> 
> Using mempool would become bit more complex here because I cannot assume about the number of elements
> during the allocation. I would use GFP_NOIO.
> 
> CC: Mike Christie <michaelc cs wisc edu>
> CC: Rob Evers <revers redhat com>
> CC: Chandra Seetharaman <chandra seetharaman us ibm com>
> Signed-off-by: Babu Moger <babu moger lsi com>
> 
> ---
> --- linux-2.6.33-rc2/drivers/scsi/device_handler/scsi_dh_rdac.c.orig	2010-01-05 11:49:22.000000000 -0400
> +++ linux-2.6.33-rc2/drivers/scsi/device_handler/scsi_dh_rdac.c	2010-01-05 11:53:13.000000000 -0400
> @@ -624,7 +624,7 @@ static int queue_mode_select(struct scsi
>  	struct rdac_queue_data *qdata;
>  	struct rdac_controller *ctlr;
>  
> -	qdata = kzalloc(sizeof(*qdata), GFP_KERNEL);
> +	qdata = kzalloc(sizeof(*qdata), GFP_NOIO);
>  	if (!qdata)
>  		return SCSI_DH_RETRY;
>  
> 
> 
> 
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