Linux-kernel mailing list archive 2000-06,: Re: 2.4 Features

# Re: 2.4 Features

Riley Williams (rhw@MemAlpha.CX)
Wed, 9 Feb 2000 20:21:17 +0000 (GMT)

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Hi Peter.

>>> Thinking about the implications of an indirection layer, I don't
>>> see any. E2compr doesn't use more than a real physical page of
>>> memory at a time?

>> Yes, it does. And that's where the pain comes. File is divided
>> into groups of pages and every group is compressed separately.

> Surely this is compression algorithm dependent! AFAIR all the
> compression algorithms avaiolable in e2compr are block
> compression algorithms. Plenty of them can be blocked 4K at a
> time.

They all can be - or 8K at a time on processors with 8K pages.

> If I remember even more correctly, that is one of the default
> choices (and if I remember even more and more correctly, I
> usually change it to 32K to get better ratios, since gzip is
> fast on decompress, and my cpu is faster on compress than the
> disk is on write).

That is indeed one of the compile-time options, and the current
default is 32k blocks.

> If the above is right, then all one has to do for the moment is
> disable e2compr compression blocks of more than PAGESIZE.

That would be one way of dealing with the problem.

Best wishes from Riley.

* Copyright (C) 1999, Memory Alpha Systems.
* All rights and wrongs reserved.

+----------------------------------------------------------------------+
| There is something frustrating about the quality and speed of Linux |
| development, ie., the quality is too high and the speed is too high, |
| in other words, I can implement this XXXX feature, but I bet someone |
| else has already done so and is just about to release their patch. |
+----------------------------------------------------------------------+
* http://www.memalpha.cx/Linux/Kernel/

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