linux-kernel - Re: [PATCH] [RFC] UBI: Implement Fastmap support

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Message-ID: <4FBE0770.60702@nod.at>
Date:	Thu, 24 May 2012 12:03:28 +0200
From:	Richard Weinberger <richard@....at>
To:	Shmulik Ladkani <shmulik.ladkani@...il.com>
CC:	dedekind1@...il.com, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Heinz.Egger@...utronix.de,
	tim.bird@...sony.com, tglx@...utronix.de
Subject: Re: [PATCH] [RFC] UBI: Implement Fastmap support

On 24.05.2012 11:56, Shmulik Ladkani wrote:
> Hi Artem,
>
> On Thu, 24 May 2012 11:17:52 +0300 Artem Bityutskiy<dedekind1@...il.com>  wrote:
>> On Tue, 2012-05-22 at 18:55 +0200, Richard Weinberger wrote:
>>>>> +    e = find_early_wl_entry(&ubi->free, max_pnum);
>>>>
>>>> This picks the eb with the lowest pnum within 'ubi->free'.
>>>>
>>>> When called with INT_MAX (for the FM_DATA), why do you need to pick
>>> a
>>>> free eb with the minimal pnum? The FM_DATA EBs may reside everywhere
>>> (as
>>>> the FM_SB holds their location).
>>>> So why not pick the eb with a medium EC value (as done for standard
>>>> get_peb calls)? That might be better wear-leveling wise.
>>>
>>> Fair point.
>>> I'll fix that.
>>> Artem, any comments on that?
>>
>> The 'find_early_wl_entry()' function is used (currently) only at early
>> stages. At these stages the we do not have the PEBs sorted by EC. We
>> have just a list. This function should not be use after the WL subsystem
>> is initialized.
>
> 'find_early_wl_entry' is only called from 'ubi_wl_get_fm_peb'.

Correct.

> 'ubi_wl_get_fm_peb' is called twice from within 'ubi_update_fastmap':
> First call, to get the FM_SB, with 'max_pnum' set as UBI_FM_MAX_START.
> Second, to get FM_DATA pebs, with 'max_pnum' as -1, do indicate "no
> matter the location, give me pebs from the free pool".

Correct. Maybe I should rename find_early_wl_entry() to 
find_wl_entry_for_fastmap() or something like that...

> 'ubi_update_fastmap' is called from 'ubi_volume_notify' and from
> 'ubi_wl_get_peb' - at both points, I assume ubi->free rbtree is properly
> populated. Am I mistaken?

Also correct.

Thanks,
//richard

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