[PATCH v3 3/5] malloc: Arena is not needed for tcache path in free()

[H.J. Lu]

On Mon, Nov 25, 2024 at 6:34 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Aug 29, 2024 at 2:31 PM Wangyang Guo <wangyang.guo@intel.com> wrote:
> >
> > Arena is not needed for _int_free_check() in non-DEBUG mode. This commit
> > defers arena deference to _int_free_chunk() thus accelerate tcache path.
> > When DEBUG enabled, arena can be obtained from p in do_check_inuse_chunk().
> >
> > Result of bench-malloc-thread benchmark
> >
> > Test Platform: Xeon-8380
> > Ratio: New / Original time_per_iteration (Lower is Better)
> >
> > Threads#   | Ratio
> > -----------|------
> > 1 thread   | 0.994
> > 4 threads  | 0.968
> >
> > The data shows it can brings 3% performance gain in multi-thread scenario.
> >
> > ---
> > Changes in v2:
> > - _int_free_check() should be put outside of USE_TCACHE.
> > - Link to v1: https://sourceware.org/pipermail/libc-alpha/2024-August/159360.html
> > ---
> >  malloc/malloc.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/malloc/malloc.c b/malloc/malloc.c
> > index 264f35e1a3..efb5292e9f 100644
> > --- a/malloc/malloc.c
> > +++ b/malloc/malloc.c
> > @@ -2143,6 +2143,9 @@ do_check_inuse_chunk (mstate av, mchunkptr p)
> >  {
> >    mchunkptr next;
> >
> > +  if (av == NULL)
> > +    av = arena_for_chunk (p);
> > +
> >    do_check_chunk (av, p);
> >
> >    if (chunk_is_mmapped (p))
> > @@ -3447,9 +3450,10 @@ __libc_free (void *mem)
> >        /* Mark the chunk as belonging to the library again.  */
> >        (void)tag_region (chunk2mem (p), memsize (p));
> >
> > -      ar_ptr = arena_for_chunk (p);
> >        INTERNAL_SIZE_T size = chunksize (p);
> > -      _int_free_check (ar_ptr, p, size);
> > +      /* av is not needed for _int_free_check in non-DEBUG mode,
> > +        in DEBUG mode, av will fetch from p in do_check_inuse_chunk.  */
> > +      _int_free_check (NULL, p, size);
>
> If _int_free_check doesn't need av, can you push it further down?
>

Something like this?

-- 
H.J.
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