Re: [PATCH] mm: slub: do not warn when allocating slab obj extensions fails

[Suren Baghdasaryan <surenb@google.com>]

On Wed, May 21, 2025 at 9:21 AM Usama Arif <usamaarif642@gmail.com> wrote:
>
>
>
> On 21/05/2025 17:02, Suren Baghdasaryan wrote:
> > On Wed, May 21, 2025 at 7:25 AM Usama Arif <usamaarif642@gmail.com> wrote:
> >>
> >> In memory bound systems, a large number of warnings for failing this
> >> allocation repeatedly may mask any real issues in the system
> >> during memory pressure being reported in dmesg. Failing this
> >> allocation is not indicative of a bug, so remove the warning.
> >>
> >> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> >> Reported-by: Vlad Poenaru <vlad.wing@gmail.com>
> >> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/
> >> ---
> >> v1 -> v2:
> >> - remove the warning completely. We will have a way in the
> >>   future to indicate that the mem alloc profile is inaccurate.
> >> ---
> >>  mm/slub.c | 4 +---
> >>  1 file changed, 1 insertion(+), 3 deletions(-)
> >>
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index dc9e729e1d26..06ab9a558b73 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -2102,9 +2102,7 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
> >>
> >>         slab = virt_to_slab(p);
> >>         if (!slab_obj_exts(slab) &&
> >> -           WARN(alloc_slab_obj_exts(slab, s, flags, false),
> >> -                "%s, %s: Failed to create slab extension vector!\n",
> >> -                __func__, s->name))
> >> +           alloc_slab_obj_exts(slab, s, flags, false))
> >
> > I thought we agreed to having pr_warn_once() here. Did I miss something?
> >
>
> I had [1] yesterday but I saw Johannes's mail [2] in and Harry mentioned in [3] that
> failing to allocate the extension vector can happen during normal operations. So I
> thought maybe there are more votes for removing it.
>
> I am ok with either pr_warn_once or removing it completely.

I feel like we should have at least some indication that something
went wrong here.

>
> I guess the question is, is it considered OK to fail here?

Well, it's not ok but not catastrophic either, so warning seems
appropriate to me.

>
> [1] https://lore.kernel.org/all/64b19c8f-e02e-490b-b987-9a996f36be21@gmail.com/
> [2] https://lore.kernel.org/all/20250520171814.GC773385@cmpxchg.org/
> [3] https://lore.kernel.org/all/20250520171814.GC773385@cmpxchg.org/