linux-kernel - Re: [PATCH 1/7] UBI: fix refill_wl_user

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Message-ID: <524D9CE1.8040600@nod.at>
Date:	Thu, 03 Oct 2013 18:35:45 +0200
From:	Richard Weinberger <richard@....at>
To:	dedekind1@...il.com
CC:	richard.genoud@...il.com, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] UBI: fix refill_wl_user_pool()

Am 03.10.2013 18:00, schrieb Artem Bityutskiy:
> On Thu, 2013-10-03 at 17:53 +0200, Richard Weinberger wrote:
>> Am 03.10.2013 17:27, schrieb Artem Bityutskiy:
>>> On Thu, 2013-10-03 at 17:08 +0200, Richard Weinberger wrote:
>>>> Am 03.10.2013 17:00, schrieb Artem Bityutskiy:
>>>>> On Sat, 2013-09-28 at 15:55 +0200, Richard Weinberger wrote:
>>>>>> If no free PEBs are available refill_wl_user_pool() must not
>>>>>> return with -ENOSPC immediately.
>>>>>> It has to block till produce_free_peb() produced a free PEB.
>>>>>>
>>>>>> Reported-and-Tested-by: Richard Genoud <richard.genoud@...il.com>
>>>>>> Signed-off-by: Richard Weinberger <richard@....at>
>>>>>
>>>>> What is pool size, I wonder?
>>>>
>>>> Currently it's 25 (UBI_FM_WL_POOL_SIZE).
>>>> If experience shows that 25 is too low/big we can change this constant.
>>>> Maybe it's also worth making them configurable...
>>>
>>> I if it is a possible scenario that this function will not return until
>>> 25 (or even 10) PEBs are erased? 
>>>
>>
>> Sure. It will try to gain up to 25 PEBs but return if it gets less.
>> That's why a pool has a current and a max size.
> 
> So if erasing speed is say, 250ms, then it would take 6.25 seconds?

Only in the very worst case if we have to call 25 times produce_free_peb().

Of course we could add a check to return immediately if produce_free_peb()
got called a few times in series.
But I really would like to wait with such performance tweaks until fastmap
is more mature.

Thanks,
//richard
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