linux-kernel - Re: [PATCH] UBIFS: add crypto lookup field to tree node cache

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Message-ID: <1337020106.2042.2.camel@koala>
Date:	Mon, 14 May 2012 21:28:26 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Joel Reardon <joel@...mbassador.com>
Cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UBIFS: add crypto lookup field to tree node cache

On Mon, 2012-05-14 at 19:20 +0200, Joel Reardon wrote:
> The long long is divided as follows:
> 32 bits for the (KSA-relative) LEB number, 32 bits for the offset in the
> leb where the key is found. So its the same as the lnum/offs for the
> current one. Theres substancial compression though, that is available,
> since theres likely not more than 2^^32 LEBS for the KSA and the number of
> bits needed for key offset is LEB_SHIFT - 4.
> 
> Is 32 bits sufficient to address all keys:
> one key per datanode means 4096 * 2^32 = 2^44, so only 16 TB available
> for 32 bit key addresses.
> 
> Though there is similar waste for lnum/offs as well. Perhaps zbranches can
> be stored as a u8[] and demarshalled with bit-op macros when needed for
> computations.

OK, thanks for explanation. Why not to then store 2x32-bit fields
instead, which is consistent with the current style? Why "long long"?

-- 
Best Regards,
Artem Bityutskiy

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