Message-ID: <4FB38683.7030306@nod.at>
Date: Wed, 16 May 2012 12:50:43 +0200
From: Richard Weinberger <richard@nod.at>
User-Agent: Mozilla/5.0 (X11; Linux i686; rv:12.0) Gecko/20120421 Thunderbird/12.0
MIME-Version: 1.0
To: dedekind1@gmail.com
CC: linux-mtd@lists.infradead.org, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, Heinz.Egger@linutronix.de,
        tim.bird@am.sony.com
Subject: Re: [RFC v4] UBI: Fastmap support (aka checkpointing)
References: <1337101871-31181-1-git-send-email-richard@nod.at> <1337161096.24809.36.camel@sauron.fi.intel.com>
In-Reply-To: <1337161096.24809.36.camel@sauron.fi.intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1426
Lines: 35

On 16.05.2012 11:38, Artem Bityutskiy wrote:
  >> This case can happen if the complete fastmap fits into one PEB, the 
fastmap
>> super block is the first PEB on the MTD partition and the fastmap pool is empty.
>> On the other side, in the worst case fastmap has to scan UBI_FM_MAX_START +
>> UBI_FM_MAX_BLOCKS + UBI_FM_MAX_POOL_SIZE PEBs.
>
> When N ->  inf, UBI_FM_MAX_BLOCKS ->  inf as well. Each PEB requires
> little space in the fastmap table.

No, UBI_FM_MAX_BLOCKS does *not* depend on the MTD partition size.
When N -> inf, UBI_FM_MAX_BLOCKS is still a constant.
--> O(1)

> O(N) would be: N ->  inf, UBI_FM_MAX_BLOCKS ->  C, where C is a constant.
>
> Or did I completely forgot math basics?
>
>> With the current default settings this would be 192 PEBs.
>> So, attaching via fastmap has a complexity of O(1).
>
> No :-) Again, for each PEB you have a little data structure in a fastmap
> which you have to (a) store, (b) read, and (c) process when attaching
> the device. The more PEBs you have, the more you do.

The maximum size of a fastmap is limited to UBI_FM_MAX_BLOCKS.
As I said, in worst case we'd have to scan 192 PEBs, which is a constant.

Thanks,
//richard
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/