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Re: Multithreaded disk access

From Dimiter_Popoff <dp@tgi-sci.com>
Newsgroups comp.arch.embedded
Subject Re: Multithreaded disk access
Date 2021-10-19 00:46 +0300
Organization TGI
Message-ID <skkpv8$8cc$1@dont-email.me> (permalink)
References (2 earlier) <ski5q2$77e$1@dont-email.me> <ski6vd$hf1$1@dont-email.me> <skk2fr$ooe$1@dont-email.me> <skk753$tmp$1@dont-email.me> <skkmg9$hl3$1@dont-email.me>

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On 10/18/2021 23:46, Don Y wrote:
> On 10/18/2021 9:25 AM, Dimiter_Popoff wrote:
>> The devil is not that black (literally translating a Bulgarian saying)
>> as you see. Worst fit allocation is of course crucial to get to
>> such figures, the mainstream OS-s don't do it and things there
>> must be much worse.
> 
> I think a lot depends on the amount of "churn" the filesystem
> experiences, in normal operation.  E.g., the "system" disk on
> the workstation I'm using today has about 800G in use of 1T total.
> But, the vast majority of it is immutable -- binaries, libraries,
> etc.  So, there's very low fragmentation (because I "build" the
> disk in one shot, instead of incrementally revising and
> "updating" its contents)

Typically so on most systems, I expect.

> 
> By contrast, the other disks in the machine all see a fair bit of
> turnover as things get created, revised and deleted.

Now this is where the worst fit allocation strategy becomes the game
changer. A newly created file is almost certainly contiguously
allocated; fragmentation occurs when it is appended to (and the
space past its last block has been already allocated in the meantime).
I think I saw somewhere (never really got interested) that mainstream
operating systems of today do just first fit - which means once you
delete a file, no matter how small, its space will be allocated as
part of the next request etc., no idea why they do it (if they do so,
my memory on that is not very certain) in such a primitive manner
but here they are.

======================================================
Dimiter Popoff, TGI             http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/

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Thread

Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-15 07:08 -0700
  Re: Multithreaded disk access Richard Damon <Richard@Damon-Family.org> - 2021-10-15 11:38 -0400
    Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-15 09:00 -0700
      Re: Multithreaded disk access Richard Damon <Richard@Damon-Family.org> - 2021-10-15 12:48 -0400
        Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-15 11:40 -0700
  Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-15 18:46 +0300
    Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-15 09:19 -0700
      Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-15 19:28 +0300
  Re: Multithreaded disk access Brett <ggtgp@yahoo.com> - 2021-10-17 20:27 +0000
    Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-17 14:49 -0700
      Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-17 15:01 -0700
      Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-18 01:09 +0300
        Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-18 08:05 -0700
          Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-18 19:25 +0300
            Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-18 13:46 -0700
              Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-19 00:46 +0300
                Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-18 16:17 -0700
                Re: Multithreaded disk access antispam@math.uni.wroc.pl - 2021-10-31 19:21 +0000
                Re: Multithreaded disk access Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-31 21:55 +0200
              Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-25 04:19 -0700
                Re: Multithreaded disk access Richard Damon <Richard@Damon-Family.org> - 2021-10-25 20:23 -0400
                Re: Multithreaded disk access Don Y <blockedofcourse@foo.invalid> - 2021-10-25 22:29 -0700
      Re: Multithreaded disk access Clifford Heath <no.spam@please.net> - 2021-10-18 11:58 +1100

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