2017-12-30 11:14 GMT+03:00 Dmitrii Tcvetkov <demfloro@xxxxxxxxxxx>:
> On Sat, 30 Dec 2017 03:15:20 +0300
> Timofey Titovets <nefelim4ag@xxxxxxxxx> wrote:
>
>> 2017-12-29 22:14 GMT+03:00 Dmitrii Tcvetkov <demfloro@xxxxxxxxxxx>:
>> > On Fri, 29 Dec 2017 21:44:19 +0300
>> > Dmitrii Tcvetkov <demfloro@xxxxxxxxxxx> wrote:
>> >> > +/**
>> >> > + * guess_optimal - return guessed optimal mirror
>> >> > + *
>> >> > + * Optimal expected to be pid % num_stripes
>> >> > + *
>> >> > + * That's generaly ok for spread load
>> >> > + * Add some balancer based on queue leght to device
>> >> > + *
>> >> > + * Basic ideas:
>> >> > + * - Sequential read generate low amount of request
>> >> > + * so if load of drives are equal, use pid % num_stripes
>> >> > balancing
>> >> > + * - For mixed rotate/non-rotate mirrors, pick non-rotate as
>> >> > optimal
>> >> > + * and repick if other dev have "significant" less queue
>> >> > lenght
>> >> > + * - Repick optimal if queue leght of other mirror are less
>> >> > + */
>> >> > +static int guess_optimal(struct map_lookup *map, int optimal)
>> >> > +{
>> >> > + int i;
>> >> > + int round_down = 8;
>> >> > + int num = map->num_stripes;
>> >>
>> >> num has to be initialized from map->sub_stripes if we're reading
>> >> RAID10, otherwise there will be NULL pointer dereference
>> >>
>> >
>> > Check can be like:
>> > if (map->type & BTRFS_BLOCK_GROUP_RAID10)
>> > num = map->sub_stripes;
>> >
>> >>@@ -5804,10 +5914,12 @@ static int __btrfs_map_block(struct
>> >>btrfs_fs_info *fs_info,
>> >> stripe_index += mirror_num - 1;
>> >> else {
>> >> int old_stripe_index = stripe_index;
>> >>+ optimal = guess_optimal(map,
>> >>+ current->pid %
>> >>map->num_stripes);
>> >> stripe_index = find_live_mirror(fs_info, map,
>> >> stripe_index,
>> >> map->sub_stripes,
>> >> stripe_index +
>> >>- current->pid %
>> >>map->sub_stripes,
>> >>+ optimal,
>> >> dev_replace_is_ongoing);
>> >> mirror_num = stripe_index - old_stripe_index
>> >> + 1; }
>> >>--
>> >>2.15.1
>> >
>> > Also here calculation should be with map->sub_stripes too.
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe
>> > linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx
>> > More majordomo info at http://vger.kernel.org/majordomo-info.html
>>
>> Why you think we need such check?
>> I.e. guess_optimal always called for find_live_mirror()
>> Both in same context, like that:
>>
>> if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
>> u32 factor = map->num_stripes / map->sub_stripes;
>>
>> stripe_nr = div_u64_rem(stripe_nr, factor, &stripe_index);
>> stripe_index *= map->sub_stripes;
>>
>> if (need_full_stripe(op))
>> num_stripes = map->sub_stripes;
>> else if (mirror_num)
>> stripe_index += mirror_num - 1;
>> else {
>> int old_stripe_index = stripe_index;
>> stripe_index = find_live_mirror(fs_info, map,
>> stripe_index,
>> map->sub_stripes, stripe_index +
>> current->pid % map->sub_stripes,
>> dev_replace_is_ongoing);
>> mirror_num = stripe_index - old_stripe_index + 1;
>> }
>>
>> That useless to check that internally
>
> My bad, so only need to call
> guess_optimal(map, current->pid % map->sub_stripes)
> in RAID10 branch.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
Yes, my bad, copy-paste error, will be fixed in v3
Thanks
--
Have a nice day,
Timofey.
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
