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

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

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.


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>  wrote:
>>> 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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