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Re: [Gcl-devel] efficiency of package symbol tables


From: Bruno Haible
Subject: Re: [Gcl-devel] efficiency of package symbol tables
Date: Tue, 23 Mar 2004 12:25:51 +0100
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Camm Maguire wrote:
> we get the much improved

Yes, that's what I meant.

> There is of course the issue of what the
> ratios of free pages to total used pages should be per type.

Is there a criterion which would let you decide that, say, it's more
welcome to allocate new STRING pages than new CONS pages before doing
a GC?

Up to now, I can see two leading criteria:

  1) The Lisp process wants to not waste time doing GC, and therefore
     allows itself to wait longer for doing GC when the GC is expected
     to be costly.

  2) The other processes on the system expect the Lisp process to be
     economic with memory, i.e. to not waste more than a given percentage
     of what it actually needs.

For criterion 2, the type of a page makes no difference (because it is
not perceived outside the Lisp process), i.e. all page types should be
handled equally.

For criterion 1, a STRING page costs less than a CONS page, therefore it
should be allowed to consume some more STRING pages than CONS pages before
triggering a GC.

Therefore what I would do is to measure the relative GC cost of each type
of page, compute percentages according to criterion 1, and then finally
move these percentages closer together to account for criterion 2.

Bruno





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