Re: [Qemu-devel] [PATCHv7 10/17] block: honour BlockLimits in bdrv_co_discard

[Peter Lieven <pl@kamp.de>]

On 11.11.2013 14:20, Kevin Wolf wrote:
> Am 24.10.2013 um 12:06 hat Peter Lieven geschrieben:
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>> Signed-off-by: Peter Lieven <pl@kamp.de>
>> ---
>>   block.c |   37 ++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/block.c b/block.c
>> index 0c0b0ac..b28dd42 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -4234,6 +4234,11 @@ static void coroutine_fn bdrv_discard_co_entry(void *opaque)
>>       rwco->ret = bdrv_co_discard(rwco->bs, rwco->sector_num, rwco->nb_sectors);
>>   }
>>   
>> +/* if no limit is specified in the BlockLimits use a default
>> + * of 32768 512-byte sectors (16 MiB) per request.
>> + */
>> +#define MAX_DISCARD_DEFAULT 32768
>> +
>>   int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
>>                                    int nb_sectors)
>>   {
>> @@ -4255,7 +4260,37 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
>>       }
>>   
>>       if (bs->drv->bdrv_co_discard) {
>> -        return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
>> +        int max_discard = bs->bl.max_discard ?
>> +                          bs->bl.max_discard : MAX_DISCARD_DEFAULT;
>> +
>> +        while (nb_sectors > 0) {
>> +            int ret;
>> +            int num = nb_sectors;
>> +
>> +            /* align request */
>> +            if (bs->bl.discard_alignment &&
>> +                num >= bs->bl.discard_alignment &&
>> +                sector_num % bs->bl.discard_alignment) {
>> +                if (num > bs->bl.discard_alignment) {
>> +                    num = bs->bl.discard_alignment;
>> +                }
>> +                num -= sector_num % bs->bl.discard_alignment;
>> +            }
>> +
>> +            /* limit request size */
>> +            if (num > max_discard) {
>> +                num = max_discard;
>> +            }
>> +
>> +            ret = bs->drv->bdrv_co_discard(bs, sector_num, num);
>> +            if (ret) {
>> +                return ret;
>> +            }
>> +
>> +            sector_num += num;
>> +            nb_sectors -= num;
>> +        }
>> +        return 0;
>>       } else if (bs->drv->bdrv_aio_discard) {
>>           BlockDriverAIOCB *acb;
>>           CoroutineIOCompletion co = {
> You're only optimising drivers which have a .bdrv_co_discard()
> implementation, but not those with .bdrv_aio_discard(). Not very nice,
> and it would have been easy to avoid this by putting the loop around the
> whole if statement instead of inside the 'then' branch.
Good point. I wonder noone noticed before ;-)

Do you want me to respin or is ok to send a follow up patch?
Stefan has it already in block-next. This patch doesn't make
the situation worse and we need follow up patches for
all the drivers to supply alignment information anyway.

Peter