Re: [Xen-devel] [PATCH RFC] Persistent grant maps for xen blkdrivers

[Jan Beulich]

>>> On 23.10.12 at 20:50, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> wrote:
> On Tue, Oct 23, 2012 at 08:09:27PM +0200, Roger Pau Monnà wrote:
>> On 23/10/12 19:20, Konrad Rzeszutek Wilk wrote:
>> >>>> diff --git a/drivers/block/xen-blkback/blkback.c 
> b/drivers/block/xen-blkback/blkback.c
>> >>>> index c6decb9..2b982b2 100644
>> >>>> --- a/drivers/block/xen-blkback/blkback.c
>> >>>> +++ b/drivers/block/xen-blkback/blkback.c
>> >>>> @@ -78,6 +78,7 @@ struct pending_req {
>> >>>>       unsigned short          operation;
>> >>>>       int                     status;
>> >>>>       struct list_head        free_list;
>> >>>> +     unsigned int            unmap_seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> 
>> Should I change this to a bool? Since we are only setting it to 0 or 1.
> 
> I would just keep it as 'int'. Eventually we can replace this with a
> bit-map, but that can be done later.

I think this should be a bitmap from the beginning - why would
you want to waste 44 bytes per request for something that fits
in a single unsigned long (and the picture would get worse with
the number-of-segments extension)?

Also - am I taking this work being done here as a silent agreement
to not invest into blkif2 to streamline the various extensions
floating around?

Jan
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