[U-Boot] [PATCH] lib/hashtable.c: add algorithm for small buffer import

[Wolfgang Denk]

Dear =?iso-8859-1?Q?Andreas_Bie=DFmann?=,

In message <8AE7E072-8389-49CA-B6C7-6C15C1877625 at googlemail.com> you wrote:
> 
> > With your configuration, importing a 64 kB environment buffer would
> > result in 32 k entries in the hash table.
> 
> Well therefore we have another 'algorithm' implemented to cope with
> this. The flag H_ALG_SMALL_BUF should be set especially when importing a
> small buffer. Anyhow the maximum limit some lines below will never be
> exceeded.

Well, you were talking about your defualt environment settings only.
How big is the envrionment in your persistent storage (flash)? I bet
it's at least several KB, resulting in thousands of entries in the
hash table.

> > This obviously makes no
> > sense.
> > 
> > I think we should rather make sure that a certain minimum of entries
> > will always be available, for exmaple something like this:
> > 
> > 		int nent = 64 + size / 8;
> 
> This sounds also good but why do not calculate as before and after that
> check some (maybe definable) borders?
> 
> How about:
> int nent = size / 8;
> if (nent < CONFIG_ENV_MIN_ENTRIES)
>  nent = CONFIG_ENV_MIN_ENTRIES;

I cannot really proof it, but I am pretty much convinced that we
should start with a non-zero constant and rather use a less steep
increase.

> Well in most cases the environment needs a static size. The actual size
> of environment has (in my view) no/small connection to space for
> environment in NV memory. In most cases the space reserved for
> environment is way to big cause of sector boundaries. Therefore I think

This is not true. Sector sizes affect only the CONFIG_ENV_SECT_SIZE
settings, while the environment size is determined by CONFIG_ENV_SIZE
which usually is MUCH smaller.

Example: "TQM5200.h":

	#define CONFIG_ENV_SIZE         0x4000  /* 16 k - keep small for fast booting */
	...
	#define CONFIG_ENV_SECT_SIZE    0x40000

> it would meet the needs when we have one (configurable) size for hash
> table without the calculation.

I disagree. Have a look at the "env import" and "env export" commands
and think about what you can do with these - essentially they lift the
fix connection to a pre-configured environment storage. Even if you
have just 2 or 4 KiB environment settings in flash, you can now just
load a file (over network, from USB stick or SDCard etc.) which may
contain tons of commands and macro definitions.

Even if you don't have such usage in mind, I do not want to make this
impossible by a too limited design.

Best regards,

Wolfgang Denk

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