Re: [patch] reiser4: port for Linux-4.1

[Edward Shishkin <edward.shishkin@gmail.com>]

On 04/06/2016 06:54 PM, Ivan Shapovalov wrote:
> On 2016-02-09 at 18:53 +0100, Edward Shishkin wrote:
>> Hi all,
>>
>> There is a pending patch for precise discarsd, which I can not merge
>> because it is incomplete. Just want to know, is there any progress on
>> this?
>>
>> So we found that calculating discard params by mkfs and storing
>> them in superblock is a dirty option, so I suggest to reserve a
>> contiguous area (1 MiB?) on disk at "mkfs -d" time (just mark it busy
>> in the bitmap). And calculate erase unit size and offset at mount
>> time.
>> If calculation failed for some reasons, then use non-precise discard.
>>
>> So, I think, we'll need one d32 field in disk superblock, which
>> indicates
>> number of reserved blocks (0 means no reservation) and a pair of
>> definitions in disk_format40.h:
>>
>> #define FORMAT40_FIRST_RESERVED_FOR_PROBING \
>>         ((REISER4_MASTER_OFFSET / PAGE_CACHE_SIZE) + 6)
>> #define FORMAT40_MAX_BLOCKS_RESERVED_FOR_PROBING
>>
>> If any questions, or technical stoppers, then let me know.
>>
>> Thanks,
>> Edward.
> I guess it would be nicer to allocate the needed space dynamically at
> mount time.


And if no enough space, then switch to non-precise discard mode? OK.
Since the probing code is for SSD drives, it shouldn't lead to long mounts
in the case of big terabyte partitions, which are full of data.


>   However, there is a problem: where to put the probing code
> in the fill_super() (I suppose?) sequence?


Put it in try_init_format40(), right after the sa_init_allocator():
seems to be a right place.

Thanks,
Edward.


>   We want the allocator to be
> intact, but nothing should be written to the filesystem so far.
>
> --
> Ivan Shapovalov / intelfx /
>
>>
>> On 07/05/2015 05:13 PM, Ivan Shapovalov wrote:
>>> On 2015-07-05 at 16:06 +0200, Dušan Čolić wrote:
>>>> On 5 Jul 2015 15:12, "Ivan Shapovalov"<intelfx100@gmail.com>  wro
>>>> te:
>>>>> On 2015-07-05 at 02:33 +0800, Edward Shishkin wrote:
>>>>>> On 07/05/2015 01:53 AM, Ivan Shapovalov wrote:
>>>>>>> On 2015-07-04 at 15:53 +0800, Edward Shishkin wrote:
>>>>>>>> [...]
>>>>>>>> And how to test directly at mount time?
>>>>>>> Something along the lines of
>>>>>>> - allocate 1 MiB of contiguous space
>>>>>>> - fill it with non-zeros
>>>>>>> - for N = 1, 2, 4, ...:
>>>>>>>      - discard N sectors from the contiguous space
>>>>>>>      - check if anything in the discarded space became zero
>>>>>>> -filled
>>>>>>>      - if it did, infer alignnment from the first zero-
>>>>>>> filled
>>>>>>> block,
>>>>>>>        infer granularity from the zero-filled region size.
>>>>>> mkfs seems to be more suitable for this funny business
>>>>> Yeah, sure. So... new superblock format with two extra fields?
>>>>>
>>>> But what happens when someone makes an image of whole partition
>>>> and
>>>> uses it
>>>> on new different ssd?
>>> Maybe we can make a tunefs.reiser4 (just) for that purpose.

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