Re: [PATCH] Decrease hash table memory overhead

From: Linus Torvalds (
Date: Tue Aug 01 2000 - 12:21:46 EST

In article <Pine.LNX.4.21.0008011530400.997-300000@saturn.homenet>,
Tigran Aivazian <> wrote:
>On Tue, 1 Aug 2000, Mark Hemment wrote:
>> I've attached a patch (against 2.4.0-test5) for the page cache, which
>> [skip]
>Hi Mark,
>I have just tested your patch against 2.4.0-test6-pre1 and the results are
>very nice - i.e. it significantly improves performance. I used two
>different tests and they both speak in one voice to your favour:

The performance improvement looks interesting, but I would rather see
this use the scheme that we _are_ using in some other places, namely
just doing version counts. They are, in my opinion, much simpler
conceptually, and can be validly used for many different data
structures. The cookie approach only works for some well-behaved stuff
(ie "always insert at the head" - which is obviously true in this case,
but the point being that the versioning approach works across a wide
variety of problems)

Cookies also tend to require that we make sure that the cookie is fully
initialized etc, so that nobody else uses that cookie by mistake for

That said, cookies can perform better than versioning (versioning can
cause unnecessary searches when there are multiple concurrent users etc,
as they "fight" over the version number), so I wouldn't be entirely
adverse to them. It probably depends on the exact use, and how
clean/ugly the code ends up looking..


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