linux-kernel - Re: [PATCH v1] xen/grant-table: log the lack of grants

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Date:   Thu, 13 Jul 2017 10:42:47 -0700
From:   Wengang <wen.gang.wang@...cle.com>
To:     xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Cc:     konrad.wilk@...cle.com, junxiao.bi@...cle.com
Subject: Re: [PATCH v1] xen/grant-table: log the lack of grants

Hi,

Anyone can you please review this patch?

thanks,

wengang


On 07/07/2017 11:23 AM, Wengang Wang wrote:
> log a message when we enter this situation:
> 1) we already allocated the max number of available grants from hypervisor
> and
> 2) we still need more (but the request fails because of 1)).
>
> Sometimes the lack of grants causes IO hangs in xen_blkfront devices.
> Adding this log would help debuging.
>
> Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Reviewed-by: Junxiao Bi <junxiao.bi@...cle.com>
> ---
>   drivers/xen/grant-table.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index d6786b8..2c6a911 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -42,6 +42,7 @@
>   #include <linux/delay.h>
>   #include <linux/hardirq.h>
>   #include <linux/workqueue.h>
> +#include <linux/ratelimit.h>
>   
>   #include <xen/xen.h>
>   #include <xen/interface/xen.h>
> @@ -1072,8 +1073,14 @@ static int gnttab_expand(unsigned int req_entries)
>   	cur = nr_grant_frames;
>   	extra = ((req_entries + (grefs_per_grant_frame-1)) /
>   		 grefs_per_grant_frame);
> -	if (cur + extra > gnttab_max_grant_frames())
> +	if (cur + extra > gnttab_max_grant_frames()) {
> +		pr_warn_ratelimited("xen/grant-table: max_grant_frames reached"
> +				    " cur=%u extra=%u limit=%u"
> +				    " gnttab_free_count=%u req_entries=%u\n",
> +				    cur, extra, gnttab_max_grant_frames(),
> +				    gnttab_free_count, req_entries);
>   		return -ENOSPC;
> +	}
>   
>   	rc = gnttab_map(cur, cur + extra - 1);
>   	if (rc == 0)