GNU bug report logs - #45200
Wishlist: There should be a `malloc-trim' function

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From: DJ Delorie <dj <at> redhat.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: fweimer <at> redhat.com, carlos <at> redhat.com, rudalics <at> gmx.at, hi-angel <at> yandex.ru, eliz <at> gnu.org, 45200 <at> debbugs.gnu.org
Subject: bug#45200: [PATCH] Force Glibc to free the memory freed
Date: Wed, 03 Feb 2021 23:02:05 -0500

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:
> But wouldn't glibc release that memory even without calling
> `malloc_trim` simply because it's at the top and is larger than
> `M_TRIM_THRESHOLD`?

Probably, if you disabled fastbins.  Like I said earler, I think
fastbins bypasses the top-of-heap consolidation, so the chunks might be
free'd but in the fastbin cache.  malloc_trim() flushes the fastbin
cache.

There are other ways to flush the fastbins but they're harder to
programmatically invoke (i.e. "magic rules").

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