Re: [PATCH 5/5] slab: Allocate and use per-call-site caches

[Kees Cook <kees@kernel.org>]

On Sat, Aug 17, 2024 at 09:30:58AM +0800, Xiu Jianfeng wrote:
> Hi Kees,
> 
> On 2024/8/9 15:33, Kees Cook wrote:
> > Use separate per-call-site kmem_cache or kmem_buckets. These are
> > allocated on demand to avoid wasting memory for unused caches.
> > 
> > A few caches need to be allocated very early to support allocating the
> > caches themselves: kstrdup(), kvasprintf(), and pcpu_mem_zalloc(). Any
> > GFP_ATOMIC allocations are currently left to be allocated from
> > KMALLOC_NORMAL.
> > 
> > With a distro config, /proc/slabinfo grows from ~400 entries to ~2200.
> > 
> > Since this feature (CONFIG_SLAB_PER_SITE) is redundant to
> > CONFIG_RANDOM_KMALLOC_CACHES, mark it a incompatible. Add Kconfig help
> > text that compares the features.
> > 
> > Improvements needed:
> > - Retain call site gfp flags in alloc_tag meta field to:
> >   - pre-allocate all GFP_ATOMIC caches (since their caches cannot
> >     be allocated on demand unless we want them to be GFP_ATOMIC
> >     themselves...)
> >   - Separate MEMCG allocations as well
> > - Allocate individual caches within kmem_buckets on demand to
> >   further reduce memory usage overhead.
> > 
> > Signed-off-by: Kees Cook <kees@kernel.org>
> > ---
> > Cc: Suren Baghdasaryan <surenb@google.com>
> > Cc: Kent Overstreet <kent.overstreet@linux.dev>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Pekka Enberg <penberg@kernel.org>
> > Cc: David Rientjes <rientjes@google.com>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Roman Gushchin <roman.gushchin@linux.dev>
> > Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> > Cc: linux-mm@kvack.org
> > ---
> >  include/linux/alloc_tag.h |   8 +++
> >  lib/alloc_tag.c           | 121 +++++++++++++++++++++++++++++++++++---
> >  mm/Kconfig                |  19 +++++-
> >  mm/slab_common.c          |   1 +
> >  mm/slub.c                 |  31 +++++++++-
> >  5 files changed, 170 insertions(+), 10 deletions(-)
> > 
> 
> [...]
> 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 3520acaf9afa..d14102c4b4d7 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -4135,6 +4135,35 @@ void *__kmalloc_large_node_noprof(size_t size, gfp_t flags, int node)
> >  }
> >  EXPORT_SYMBOL(__kmalloc_large_node_noprof);
> >  
> > +static __always_inline
> > +struct kmem_cache *choose_slab(size_t size, kmem_buckets *b, gfp_t flags,
> > +			       unsigned long caller)
> > +{
> > +#ifdef CONFIG_SLAB_PER_SITE
> > +	struct alloc_tag *tag = current->alloc_tag;
> 
> There is a compile error here if CONFIG_MEM_ALLOC_PROFILING is disabled
> when I test this patchset.
> 
> mm/slub.c: In function ‘choose_slab’:
> mm/slub.c:4187:40: error: ‘struct task_struct’ has no member named
> ‘alloc_tag’
>  4187 |         struct alloc_tag *tag = current->alloc_tag;
>       |                                        ^~
>   CC      mm/page_reporting.o
> 
> maybe CONFIG_SLAB_PER_SITE should depend on CONFIG_MEM_ALLOC_PROFILING

Thanks! I tried to make the Kconfig use the right dependencies, but I
clearly missed something. There is also some weird behavior between
"depends" and "select". I will get this fixed for the next version.

-Kees

-- 
Kees Cook