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

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Date:	Thu, 03 Oct 2013 19:41:55 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Richard Weinberger <richard@....at>
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()

On Thu, 2013-10-03 at 18:35 +0200, Richard Weinberger wrote:
> 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.

OK, but how about at least adding a comment talking about this unlikely
scenario?

-- 
Best Regards,
Artem Bityutskiy

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