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| From | Eric Sosman <esosman@ieee-dot-org.invalid> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Memory management and custom allocator |
| Date | 2012-01-02 09:47 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <jdsg2h$mkb$1@dont-email.me> (permalink) |
| References | (2 earlier) <LPYLq.355$EO5.173@newsfe26.ams2> <jdpp3r$8h3$1@dont-email.me> <jdqjtf$bqd$1@reader1.panix.com> <jdsact$nr6$1@dont-email.me> <CTiMq.187959$WC5.163670@newsfe09.ams2> |
On 1/2/2012 9:07 AM, BartC wrote:
>
>
> "Eric Sosman" <esosman@ieee-dot-org.invalid> wrote in message
> news:jdsact$nr6$1@dont-email.me...
>> On 1/1/2012 4:41 PM, Joe keane wrote:
>>> In article<jdpp3r$8h3$1@dont-email.me>,
>>> Eric Sosman<esosman@ieee-dot-org.invalid> wrote:
>>>> What's "sensible" about allocating in powers of two?
>>>
>>> A) VM pages are powers of two, so if you have non-two objects you waste
>>> space or take more VM pages for each object than you would like
>>>
>>> B) cache lines are powers of two, so if you have non-two objects you
>>> waste space or take more cache lines for each object than you would like
>>
>> If you have a forty-four-byte struct and allocate sixty-four
>> bytes to hold it, how have you avoided *either* sort of "waste?"
>>
>> If you have a thousand such structs, what "waste" do you avoid
>> by spending 64K instead of 44K to hold them? That is, what gain
>> repays your expenditure of an extra 20K?
>
> This is where you redesign your struct to use only 32 bytes, or find a
> good use for another 20 bytes to make 64.
Ri-i-i-ght. Pretending the extra twenty bytes are in a good cause
doesn't make them so.
> Such structs are easier to index in arrays.
Nonsense. The `[]' operator works with equal ease on arrays
of any element size at all.
> And fit nicely into those
> 32- or 64-byte blocks that memory seems to be structured as now, if also
> aligned properly, and less likely to straddle two VM pages (actually I
> don't know if that's a big deal now; it certainly has been).
The fit is not "nice" if it's attained by wasting space. (Weren't
you the guy who recently complained about malloc() adding overhead to
each block?)
As for straddling VM pages, denser packing wins over bloated "nicer"
packing any day. Consider again the example of a thousand structs: I
want to use 44KB, you're suggesting 64KB would be "nicer." Suppose an
8KB page: You want to use eight pages, I want to use six. Suppose a
64B cache line: You want to use a thousand cache lines, I want to use
six hundred eighty-eight.
> So powers-of-two are hardware-friendly. But now stick on 8- or 12-bytes
> of overhead, and it's a mess.
Wait, wait, wait: You started with 44 bytes, strained your brain
to imagine a "good use" for another twenty because you're superstitious
about powers of two), and then complained when malloc() tacked on eight
bytes of its own? Why didn't you just stick with the original 44?
> You can't design a struct to be 8- or
> 12-bytes smaller than a power-of-two; every system will be different.
You can't design it to be exactly 64 bytes, either. Quick: How
many bytes in a `long double'? What's the alignment requirement of
a function pointer? What is the "unit" size of a bit-field?
--
Eric Sosman
esosman@ieee-dot-org.invalid
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[Slightly OT] Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 06:56 -0800
Re: [Slightly OT] Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-31 11:08 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 08:28 -0800
Re: [Slightly OT] Memory management and custom allocator Johann Klammer <klammerr@NOSPAM.aon.at> - 2011-12-31 17:39 +0100
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 08:55 -0800
Re: Memory management and custom allocator Johann Klammer <klammerr@NOSPAM.aon.at> - 2011-12-31 19:01 +0100
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2011-12-31 18:31 +0000
Re: [Slightly OT] Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2011-12-31 17:24 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 09:52 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-31 14:30 -0500
Re: Memory management and custom allocator Markus Wichmann <nullplan@gmx.net> - 2012-01-01 12:21 +0100
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 12:54 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-01 09:03 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 16:23 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-01 21:41 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 08:10 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 14:07 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 09:47 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:36 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 13:43 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 11:38 -0800
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-03 13:14 +0000
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-03 06:07 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-05 17:06 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 21:36 +0000
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2012-01-02 21:44 +0000
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 23:10 -0800
Re: Memory management and custom allocator Keith Thompson <kst-u@mib.org> - 2012-01-02 13:42 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 17:38 -0500
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-02 21:45 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 18:19 -0500
Re: Memory management and custom allocator Keith Thompson <kst-u@mib.org> - 2012-01-02 15:42 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 23:59 +0000
Re: Memory management and custom allocator Kleuske <kleuske@nowhere.net> - 2012-01-03 11:38 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-03 12:49 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-04 23:42 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-04 20:23 -0500
Re: Memory management and custom allocator Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-01-05 23:31 +0200
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-04 21:52 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-04 20:31 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-05 01:45 +0000
Re: Memory management and custom allocator Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-01-07 05:55 +0200
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-07 12:02 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-01 09:08 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-01 10:08 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 23:34 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 02:18 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 02:34 -0800
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 02:43 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 03:11 -0800
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:17 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 11:40 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:27 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 23:26 +0000
Re: Memory management and custom allocator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-01 23:54 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 00:32 +0000
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2012-01-02 02:46 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 11:53 +0000
Re: Memory management and custom allocator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-02 15:18 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-03 12:21 +0000
Re: Memory management and custom allocator Karl Malbrain <malbrain@yahoo.com> - 2012-01-04 16:48 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-05 01:36 +0000
Re: [Slightly OT] Memory management and custom allocator "io_x" <a@b.c.invalid> - 2012-01-01 17:02 +0100
Re: [Slightly OT] Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-01 21:21 +0000
Re: [Slightly OT] Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-01 21:01 -0800
Re: [Slightly OT] Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-07 05:20 -0800
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