Re: [PATCH RFC 14/20] mempool: introduce mempool_use_prealloc_only

[Marco Elver]

On Thu, 23 Nov 2023 at 19:06, Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote:
>
> On Wed, Nov 22, 2023 at 6:21 PM Marco Elver <elver@xxxxxxxxxx> wrote:
> >
> > On Mon, Nov 06, 2023 at 09:10PM +0100, andrey.konovalov@xxxxxxxxx wrote:
> > > From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > >
> > > Introduce a new mempool_use_prealloc_only API that tells the mempool to
> > > only use the elements preallocated during the mempool's creation and to
> > > not attempt allocating new ones.
> > >
> > > This API is required to test the KASAN poisoning/unpoisoning functinality
> > > in KASAN tests, but it might be also useful on its own.
> > >
> > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > > ---
> > >  include/linux/mempool.h |  2 ++
> > >  mm/mempool.c            | 27 ++++++++++++++++++++++++---
> > >  2 files changed, 26 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/include/linux/mempool.h b/include/linux/mempool.h
> > > index 4aae6c06c5f2..822adf1e7567 100644
> > > --- a/include/linux/mempool.h
> > > +++ b/include/linux/mempool.h
> > > @@ -18,6 +18,7 @@ typedef struct mempool_s {
> > >       int min_nr;             /* nr of elements at *elements */
> > >       int curr_nr;            /* Current nr of elements at *elements */
> > >       void **elements;
> > > +     bool use_prealloc_only; /* Use only preallocated elements */
> >
> > This increases the struct size from 56 to 64 bytes (64 bit arch).
> > mempool_t is embedded in lots of other larger structs, and this may
> > result in some unwanted bloat.
> >
> > Is there a way to achieve the same thing without adding a new bool to
> > the mempool struct?
>
> We could split out the part of mempool_alloc that uses preallocated
> elements without what waiting part and expose it in another API
> function named something like mempool_alloc_preallocated. Would that
> be better?

Yes, that might be better. As long as other users of mempool (esp if
KASAN is disabled) are unaffected then it should be fine.