Re: [PATCH] slub: fix unreclaimable slab stat for bulk free

[Kefeng Wang]

On 2021/7/29 22:03, Shakeel Butt wrote:
> On Wed, Jul 28, 2021 at 11:52 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
> > On 2021/7/28 23:53, Shakeel Butt wrote:
> > > SLUB uses page allocator for higher order allocations and update
> > > unreclaimable slab stat for such allocations. At the moment, the bulk
> > > free for SLUB does not share code with normal free code path for these
> > > type of allocations and have missed the stat update. So, fix the stat
> > > update by common code. The user visible impact of the bug is the
> > > potential of inconsistent unreclaimable slab stat visible through
> > > meminfo and vmstat.
> > >
> > > Fixes: 6a486c0ad4dc ("mm, sl[ou]b: improve memory accounting")
> > > Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > > ---
> > >    mm/slub.c | 22 ++++++++++++----------
> > >    1 file changed, 12 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index 6dad2b6fda6f..03770291aa6b 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -3238,6 +3238,16 @@ struct detached_freelist {
> > >        struct kmem_cache *s;
> > >    };
> > >
> > > +static inline void free_nonslab_page(struct page *page)
> > > +{
> > > +     unsigned int order = compound_order(page);
> > > +
> > > +     VM_BUG_ON_PAGE(!PageCompound(page), page);
> > Could we add WARN_ON here, or we got nothing when CONFIG_DEBUG_VM is
> > disabled.
> I don't have a strong opinion on this. Please send a patch with
> reasoning if you want WARN_ON_ONCE here.

Ok, we met a BUG_ON(!PageCompound(page)) in kfree() twice in lts4.4, we 
are still debugging it.

It's different to analyses due to no vmcore, and can't be reproduced.

WARN_ON() here could help us to notice the issue.

Also is there any experience or known fix/way to debug this kinds of 
issue? memory corruption?

Any suggestion will be appreciated, thanks.



> .