Re: [PATCH v3 07/35] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj_ext creation

Suren Baghdasaryan
2024-02-16T18:42:00Z

On Thu, Feb 15, 2024 at 10:10 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Feb 15, 2024 at 1:50 PM Vlastimil Babka <vbabka@suse.cz> wrote:
> >
> > On 2/15/24 22:37, Kent Overstreet wrote:
> > > On Thu, Feb 15, 2024 at 10:31:06PM +0100, Vlastimil Babka wrote:
> > >> On 2/12/24 22:38, Suren Baghdasaryan wrote:
> > >> > Slab extension objects can't be allocated before slab infrastructure is
> > >> > initialized. Some caches, like kmem_cache and kmem_cache_node, are created
> > >> > before slab infrastructure is initialized. Objects from these caches can't
> > >> > have extension objects. Introduce SLAB_NO_OBJ_EXT slab flag to mark these
> > >> > caches and avoid creating extensions for objects allocated from these
> > >> > slabs.
> > >> >
> > >> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > >> > ---
> > >> > include/linux/slab.h | 7 +++++++
> > >> > mm/slub.c | 5 +++--
> > >> > 2 files changed, 10 insertions(+), 2 deletions(-)
> > >> >
> > >> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > >> > index b5f5ee8308d0..3ac2fc830f0f 100644
> > >> > --- a/include/linux/slab.h
> > >> > +++ b/include/linux/slab.h
> > >> > @@ -164,6 +164,13 @@
> > >> > #endif
> > >> > #define SLAB_TEMPORARY SLAB_RECLAIM_ACCOUNT /* Objects are short-lived */
> > >> >
> > >> > +#ifdef CONFIG_SLAB_OBJ_EXT
> > >> > +/* Slab created using create_boot_cache */
> > >> > +#define SLAB_NO_OBJ_EXT ((slab_flags_t __force)0x20000000U)
> > >>
> > >> There's
> > >> #define SLAB_SKIP_KFENCE ((slab_flags_t __force)0x20000000U)
> > >> already, so need some other one?
>
> Indeed. I somehow missed it. Thanks for noticing, will fix this in the
> next version.

Apparently the only unused slab flag is 0x00000200U, all others seem
to be taken. I'll use it if there are no objections.

>
> > >
> > > What's up with the order of flags in that file? They don't seem to
> > > follow any particular ordering.
> >
> > Seems mostly in increasing order, except commit 4fd0b46e89879 broke it for
> > SLAB_RECLAIM_ACCOUNT?
> >
> > > Seems like some cleanup is in order, but any history/context we should
> > > know first?
> >
> > Yeah noted, but no need to sidetrack you.