From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2120.oracle.com ([141.146.126.78]:57338 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751899AbeAaOf2 (ORCPT ); Wed, 31 Jan 2018 09:35:28 -0500 Subject: Re: [PATCH 2/2] btrfs: add read_mirror_policy parameter devid To: Nikolay Borisov , linux-btrfs@vger.kernel.org References: <20180130063020.14850-1-anand.jain@oracle.com> <20180130063020.14850-3-anand.jain@oracle.com> <7a21d5f0-b7f0-9da6-22b6-b45976d6ab40@oracle.com> <7fdfcf9a-2bc5-7f1b-1417-3ccc95cdcf83@suse.com> <27eaef30-69ae-b5a6-2cd6-9035c61615e7@oracle.com> <7eb73e78-f6ca-be5f-4505-a88d60172037@suse.com> From: Anand Jain Message-ID: Date: Wed, 31 Jan 2018 22:36:43 +0800 MIME-Version: 1.0 In-Reply-To: <7eb73e78-f6ca-be5f-4505-a88d60172037@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 01/31/2018 09:42 PM, Nikolay Borisov wrote: >>> So usually this should be functionality handled by the raid/san >>> controller I guess, > but given that btrfs is playing the role of a >>> controller here at what point are we drawing the line of not >>> implementing block-level functionality into the filesystem ? >> >>  Don't worry this is not invading into the block layer. How >>  can you even build this functionality in the block layer ? >>  Block layer even won't know that disks are mirrored. RAID >>  does or BTRFS in our case. >> > > By block layer I guess I meant the storage driver of a particular raid > card. Because what is currently happening is re-implementing > functionality that will generally sit in the driver. So my question was > more generic and high-level - at what point do we draw the line of > implementing feature that are generally implemented in hardware devices > (be it their drivers or firmware). Not all HW configs use RAID capable HBAs. A server connected to a SATA JBOD using a SATA HBA without MD will relay on BTRFS to provide all the features and capabilities that otherwise would have provided by such a presumable HW config. :: >>>> :: >>>>>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c >>>>>> index 39ba59832f38..478623e6e074 100644 >>>>>> --- a/fs/btrfs/volumes.c >>>>>> +++ b/fs/btrfs/volumes.c >>>>>> @@ -5270,6 +5270,16 @@ static int find_live_mirror(struct >>>>>> btrfs_fs_info *fs_info, >>>>>>            num = map->num_stripes; >>>>>>          switch(fs_info->read_mirror_policy) { >>>>>> +    case BTRFS_READ_MIRROR_BY_DEV: >>>>>> +        optimal = first; >>>>>> +        if (test_bit(BTRFS_DEV_STATE_READ_MIRROR, >>>>>> +                 &map->stripes[optimal].dev->dev_state)) >>>>>> +            break; >>>>>> +        if (test_bit(BTRFS_DEV_STATE_READ_MIRROR, >>>>>> +                 &map->stripes[++optimal].dev->dev_state)) >>>>>> +            break; >>>>>> +        optimal = first; >>>>> >>>>> you set optimal 2 times, the second one seems redundant. >>>> >>>>   No actually. When both the disks containing the stripe does not >>>>   have the BTRFS_DEV_STATE_READ_MIRROR, then I would just want to >>>>   use first found stripe. >>> >>> Yes, and the fact that you've already set optimal = first right after >>> BTRFS_READ_MIRROR_BY_DEV ensures that, no ? Why do you need to again set >>> optimal right before the final break? What am I missing here? >> >>   Ah. I think you are missing ++optimal in the 2nd if. > > You are right, but I'd prefer you index the stripes array with 'optimal' > and 'optimal + 1' and leave just a single assignment Ok. Will improve that. Thanks, Anand >> >> Thanks, Anand >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >