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

[Aurelien Jarno <aurelien@aurel32.net>]

On 2023-07-05 10:37, Siddhesh Poyarekar via Libc-alpha wrote:
> On 2023-07-05 07:55, Aurelien Jarno wrote:
> > 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.
> 
> Thanks, if you think the fix is OK, can you please give a Reviewed-by? I
> will then backport this to the 2.37 branch as well.

Yep, of course.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>

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