From: "Keith Packard" <keithp@keithp.com>
To: Maarten van der Schrieck | Things Connected
<maarten@thingsconnected.nl>,
newlib@sourceware.org
Subject: Re: [PATCH] nano malloc allocator algorithm improvement
Date: Sat, 22 Aug 2020 15:57:54 -0700 [thread overview]
Message-ID: <87tuwugufh.fsf@keithp.com> (raw)
In-Reply-To: <a742986b-4c4d-6d59-6433-938bc471ae7a@thingsconnected.nl>
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Maarten van der Schrieck | Things Connected <maarten@thingsconnected.nl>
writes:
> The current nano malloc implementation has two issues reducing the amount of memory available and increasing fragmentation.
>
> The first issue is that sbrk() will be called to allocate a space with
> the size of the entire requested alloc_size, even if the last free
> chunk borders the edge of currently allocated memory. This means that
> in a system with 20 kb of RAM, you will get ENOMEM when performing
> this:
Oh, that's a great idea. I did the same for realloc when the block was
at the end of the heap; doing the same for malloc is a nice
addition.
> The second issue is that a free chunk that is oversized will be cut up
> in two pieces, where the *second* piece is used for allocation and the
> first one is kept as a free chunk. Although this is easier/shorter in
> code (because the free list remains unaffected apart from the size of
> the free chunk) it leads to an inefficient pattern of memory
> allocation, and ultimately in fragmentation and slower malloc/free
> calls.
I re-worked the list management to use a different pattern that makes
this change much less invasive.
https://github.com/picolibc/picolibc/commit/fd2d18bb5ab442f16789c243648d07b4ec8e2b29
--
-keith
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next prev parent reply other threads:[~2020-08-22 22:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-22 19:40 Maarten van der Schrieck | Things Connected
2020-08-22 22:57 ` Keith Packard [this message]
2020-08-23 0:12 ` Keith Packard
2020-08-24 10:03 ` Corinna Vinschen
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