Re: Woohoo.

From: George (greerga@DRAGON.HAM.MUOHIO.EDU)
Date: 08/20/97

On Wed, 20 Aug 1997, Jeremy Elson wrote:

>George writes:
>>print_object_location:1354 requested 8192 bytes, received 12320.
>>write_to_output:987 requested 12288 bytes, received 32384. (***)
>This is a good example of why the buffer-selection policy needs more
>work, though - maybe using best fit instead of first fit.  Of course,

At this point, I had two 8,192 byte buffers. Do_where took the first, and
perform_immort_where took the second.  That left none free for
print_object_location and I didn't have a dedicated 12288 byte buffer at
the time.

A large part of this problem is that so much of the code wants a
MAX_STRING_LENGTH buffer when they really need less.  Like do_where
requested a MAX_STRING_LENGTH (8192) and uses it for one_argument which
only requires MAX_INPUT_LENGTH (256).  Once I eliminate all those cases by
evaluating all the allocations, it should be a lot bteter.

>any data structures student will tell you that no matter which policy
>you use [first fit, best fit, worst fit, next fit, etc.] you can
>construct an example in which the policy is catastrophically bad; but

do_users, do_who

>for Circle I think best fit is probably best, as long as it can be
>done quickly.  (Actually, since there are only a small number of
>possible sizes of buffers, maybe each size should be kept on its own
>linked list -- e.g. instead of a single list of type Buffer *, have an

A lot of functions request odd sizes like 200, 100, 32384, 12880, 300, etc.

>array of type *Buffers[], where Buffers[i] is the beginning of a
>linked list of buffers of size 2**i).

I think a system of:
buffer[x]       - (typical use)
0 = 128         - log messages mostly
1 = 256         - one_argument
2 = 512         - overflows
3 = 1024        - small bufsize
4 = 2048        - keep for overflow?
5 = 4096        - keep for overflow?
6 = 8192        - max_string_length, the single most requested buffer
7 = 16384       - process_output and large buffers
8 = 32768       - load_help

Then any requests over 32,768 return error (I would prefer error unless
given a valid reason to allow such huge requests) and anything less than
128 gets a 128.  Simple bit shifting (or division) would give us the size.

-- | Genius may have its limitations, but stupidity | is not thus handicapped. -- Elbert Hubbard

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