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From: Bonita Montero <Bonita.Montero@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: realloc() - frequency, conditions, or experiences about
 relocation?
Date: Mon, 24 Jun 2024 16:19:22 +0200
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Am 24.06.2024 um 11:55 schrieb Keith Thompson:
> It's not safe to assume that a shrinking realloc call will never fail.
> It's possible that it will never fail in any existing implementation,
> but the standard makes no such guarantee.

With modern memory allocators a shrink can easily fail if the shrunken
block falls into a different size class and there's no memory for a
block in this class.
mimalloc, jemalloc and TCMalloc round up the size to the next power of
two up to 8kB. If yoz have a 8kB-class block and it shrinks below 4kB
and there's no page (6kB for all mentioned allocators) for this class
and no additional pool can be allocated the shrink fails.