[PATCH] realloc: Limit chunk reuse to only growing requests [BZ #30579]

[Aurelien Jarno]

Hi,

On 2023-07-04 14:24, Siddhesh Poyarekar via Libc-alpha wrote:
> The trim_threshold is too aggressive a heuristic to decide if chunk
> reuse is OK for reallocated memory; for repeated small, shrinking
> allocations it leads to internal fragmentation and for repeated larger
> allocations that fragmentation may blow up even worse due to the dynamic
> nature of the threshold.
> 
> Limit reuse only when it is within the alignment padding, which is 2 *
> size_t for heap allocations and a page size for mmapped allocations.
> There's the added wrinkle of THP, but this fix ignores it for now,
> pessimizing that case in favor of keeping fragmentation low.
> 
> This resolves BZ #30579.
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> Reported-by: Nicolas Dusart <nicolas@freedelity.be>
> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
> 
> The test case in the bz seems fixed with this, bringing VSZ and RSS back
> to ~40M from ~1G.  Aurelien, can you please test with plasma desktop?
 
Thanks for the quick fix. I confirm that this patch fixes the issue with
plasma desktop.

Regards
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net