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Date:   Tue, 2 Aug 2022 18:22:32 +0900
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Joe Perches <joe@perches.com>,
        Vasily Averin <vasily.averin@linux.dev>,
        Matthew WilCox <willy@infradead.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 14/16] mm/slab_common: drop kmem_alloc & avoid
 dereferencing fields when not using
Message-ID: <Yujs2KVcfip2hIYe@hyeyoo>
References: <20220712133946.307181-1-42.hyeyoo@gmail.com>
 <20220712133946.307181-15-42.hyeyoo@gmail.com>
 <ec5dc308-e75f-eb4e-3837-a7221506f773@suse.cz>
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In-Reply-To: <ec5dc308-e75f-eb4e-3837-a7221506f773@suse.cz>
Precedence: bulk

On Fri, Jul 29, 2022 at 01:23:38PM +0200, Vlastimil Babka wrote:
> On 7/12/22 15:39, Hyeonggon Yoo wrote:
> > Drop kmem_alloc event class, and define kmalloc and kmem_cache_alloc
> > using TRACE_EVENT() macro.
> > 
> > And then this patch does:
> >    - Do not pass pointer to struct kmem_cache to trace_kmalloc.
> >      gfp flag is enough to know if it's accounted or not.
> >    - Avoid dereferencing s->object_size and s->size when not using kmem_cache_alloc event.
> >    - Avoid dereferencing s->name in when not using kmem_cache_free event.
> > 
> > Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> 
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> 
> With some comments:
> 
> > ---
> >  include/trace/events/kmem.h | 64 +++++++++++++++++++++++++------------
> >  mm/slab.c                   | 16 ++++------
> >  mm/slab_common.c            | 17 ++++++----
> >  mm/slob.c                   | 16 +++-------
> >  mm/slub.c                   | 13 +++-----
> >  5 files changed, 70 insertions(+), 56 deletions(-)
> > 
> > diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> > index e078ebcdc4b1..0ded2c351062 100644
> > --- a/include/trace/events/kmem.h
> > +++ b/include/trace/events/kmem.h
> > @@ -9,17 +9,15 @@
> >  #include <linux/tracepoint.h>
> >  #include <trace/events/mmflags.h>
> >  
> > -DECLARE_EVENT_CLASS(kmem_alloc,
> > +TRACE_EVENT(kmem_cache_alloc,
> >  
> >  	TP_PROTO(unsigned long call_site,
> >  		 const void *ptr,
> >  		 struct kmem_cache *s,
> > -		 size_t bytes_req,
> > -		 size_t bytes_alloc,
> >  		 gfp_t gfp_flags,
> >  		 int node),
> >  
> > -	TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node),
> > +	TP_ARGS(call_site, ptr, s, gfp_flags, node),
> >  
> >  	TP_STRUCT__entry(
> >  		__field(	unsigned long,	call_site	)
> > @@ -34,8 +32,8 @@ DECLARE_EVENT_CLASS(kmem_alloc,
> >  	TP_fast_assign(
> >  		__entry->call_site	= call_site;
> >  		__entry->ptr		= ptr;
> > -		__entry->bytes_req	= bytes_req;
> > -		__entry->bytes_alloc	= bytes_alloc;
> > +		__entry->bytes_req	= s->object_size;
> > +		__entry->bytes_alloc	= s->size;
> >  		__entry->gfp_flags	= (__force unsigned long)gfp_flags;
> >  		__entry->node		= node;
> >  		__entry->accounted	= IS_ENABLED(CONFIG_MEMCG_KMEM) ?
> 
> This assignment continues by ...
> 	(s && s->flags & SLAB_ACCOUNT)) : false;
> 
> We could now remove the "s &&" as we assume it's non-NULL anyway.

Right. will adjust. 

> 
> > @@ -53,22 +51,46 @@ DECLARE_EVENT_CLASS(kmem_alloc,
> >  		__entry->accounted ? "true" : "false")
> >  );
> >  
> > -DEFINE_EVENT(kmem_alloc, kmalloc,
> > +TRACE_EVENT(kmalloc,
> >  
> > -	TP_PROTO(unsigned long call_site, const void *ptr,
> > -		 struct kmem_cache *s, size_t bytes_req, size_t bytes_alloc,
> > -		 gfp_t gfp_flags, int node),
> > +	TP_PROTO(unsigned long call_site,
> > +		 const void *ptr,
> > +		 size_t bytes_req,
> > +		 size_t bytes_alloc,
> > +		 gfp_t gfp_flags,
> > +		 int node),
> >  
> > -	TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node)
> > -);
> > +	TP_ARGS(call_site, ptr, bytes_req, bytes_alloc, gfp_flags, node),
> >  
> > -DEFINE_EVENT(kmem_alloc, kmem_cache_alloc,
> > +	TP_STRUCT__entry(
> > +		__field(	unsigned long,	call_site	)
> > +		__field(	const void *,	ptr		)
> > +		__field(	size_t,		bytes_req	)
> > +		__field(	size_t,		bytes_alloc	)
> > +		__field(	unsigned long,	gfp_flags	)
> > +		__field(	int,		node		)
> > +		__field(	bool,		accounted	)
> > +	),
> >  
> > -	TP_PROTO(unsigned long call_site, const void *ptr,
> > -		 struct kmem_cache *s, size_t bytes_req, size_t bytes_alloc,
> > -		 gfp_t gfp_flags, int node),
> > +	TP_fast_assign(
> > +		__entry->call_site	= call_site;
> > +		__entry->ptr		= ptr;
> > +		__entry->bytes_req	= bytes_req;
> > +		__entry->bytes_alloc	= bytes_alloc;
> > +		__entry->gfp_flags	= (__force unsigned long)gfp_flags;
> > +		__entry->node		= node;
> > +		__entry->accounted	= IS_ENABLED(CONFIG_MEMCG_KMEM) ?
> > +					  (gfp_flags & __GFP_ACCOUNT) : false;
> 
> This test could be perhaps moved to TP_printk and the accounted field
> removed completely, but we need to make sure trace-cmd (which reads the
> binary entries and does the printk in userspace) can interpret the tests
> properly, including the IS_ENABLED(CONFIG_MEMCG_KMEM) part.

Okay, I'll try moving it and check if trace-cmd could understand it.

> 
> > +	),
> >  
> > -	TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node)
> > +	TP_printk("call_site=%pS ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d accounted=%s",
> > +		(void *)__entry->call_site,
> > +		__entry->ptr,
> > +		__entry->bytes_req,
> > +		__entry->bytes_alloc,
> > +		show_gfp_flags(__entry->gfp_flags),
> > +		__entry->node,
> > +		__entry->accounted ? "true" : "false")
> >  );
> >  
> >  TRACE_EVENT(kfree,
> > @@ -93,20 +115,20 @@ TRACE_EVENT(kfree,
> >  
> >  TRACE_EVENT(kmem_cache_free,
> >  
> > -	TP_PROTO(unsigned long call_site, const void *ptr, const char *name),
> > +	TP_PROTO(unsigned long call_site, const void *ptr, const struct kmem_cache *s),
> >  
> > -	TP_ARGS(call_site, ptr, name),
> > +	TP_ARGS(call_site, ptr, s),
> >  
> >  	TP_STRUCT__entry(
> >  		__field(	unsigned long,	call_site	)
> >  		__field(	const void *,	ptr		)
> > -		__string(	name,	name	)
> > +		__string(	name,		s->name		)
> >  	),
> >  
> >  	TP_fast_assign(
> >  		__entry->call_site	= call_site;
> >  		__entry->ptr		= ptr;
> > -		__assign_str(name, name);
> > +		__assign_str(name, s->name);
> >  	),
> >  
> >  	TP_printk("call_site=%pS ptr=%p name=%s",
> > diff --git a/mm/slab.c b/mm/slab.c
> > index f9b74831e3f4..1685e5507a59 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -3447,8 +3447,7 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *cachep, struct list_lru *lru,
> >  {
> >  	void *ret = slab_alloc(cachep, lru, flags, cachep->object_size, _RET_IP_);
> >  
> > -	trace_kmem_cache_alloc(_RET_IP_, ret, cachep, cachep->object_size,
> > -			       cachep->size, flags, NUMA_NO_NODE);
> > +	trace_kmem_cache_alloc(_RET_IP_, ret, cachep, flags, NUMA_NO_NODE);
> >  
> >  	return ret;
> >  }
> > @@ -3537,8 +3536,9 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
> >  	ret = slab_alloc(cachep, NULL, flags, size, _RET_IP_);
> >  
> >  	ret = kasan_kmalloc(cachep, ret, size, flags);
> > -	trace_kmalloc(_RET_IP_, ret, cachep,
> > -		      size, cachep->size, flags, NUMA_NO_NODE);
> > +	trace_kmalloc(_RET_IP_, ret,
> > +		      size, cachep->size,
> > +		      flags, NUMA_NO_NODE);
> 
> This could now fit on 2, maybe even 1 line?
> Other trace_* calls could be perhaps also reduced, please check.
>

Okay, will check.

> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(kmem_cache_alloc_trace);
> > @@ -3561,9 +3561,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid)
> >  {
> >  	void *ret = slab_alloc_node(cachep, NULL, flags, nodeid, cachep->object_size, _RET_IP_);
> >  
> > -	trace_kmem_cache_alloc(_RET_IP_, ret, cachep,
> > -			       cachep->object_size, cachep->size,
> > -			       flags, nodeid);
> > +	trace_kmem_cache_alloc(_RET_IP_, ret, cachep, flags, nodeid);
> >  
> >  	return ret;
> >  }
> > @@ -3588,7 +3586,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
> >  	ret = slab_alloc_node(cachep, NULL, flags, nodeid, size, _RET_IP_);
> >  
> >  	ret = kasan_kmalloc(cachep, ret, size, flags);
> > -	trace_kmalloc(_RET_IP_, ret, cachep,
> > +	trace_kmalloc(_RET_IP_, ret,
> >  		      size, cachep->size,
> >  		      flags, nodeid);
> >  	return ret;
> > @@ -3652,7 +3650,7 @@ void kmem_cache_free(struct kmem_cache *cachep, void *objp)
> >  	if (!cachep)
> >  		return;
> >  
> > -	trace_kmem_cache_free(_RET_IP_, objp, cachep->name);
> > +	trace_kmem_cache_free(_RET_IP_, objp, cachep);
> >  	__do_kmem_cache_free(cachep, objp, _RET_IP_);
> >  }
> >  EXPORT_SYMBOL(kmem_cache_free);
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 0e66b4911ebf..c01c6b8f0d34 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -933,7 +933,7 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
> >  
> >  	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> >  		ret = kmalloc_large_node_notrace(size, flags, node);
> > -		trace_kmalloc(_RET_IP_, ret, NULL,
> > +		trace_kmalloc(_RET_IP_, ret,
> >  			      size, PAGE_SIZE << get_order(size),
> >  			      flags, node);
> >  		return ret;
> > @@ -946,8 +946,9 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
> >  
> >  	ret = __kmem_cache_alloc_node(s, flags, node, size, caller);
> >  	ret = kasan_kmalloc(s, ret, size, flags);
> > -	trace_kmalloc(_RET_IP_, ret, s, size,
> > -		      s->size, flags, node);
> > +	trace_kmalloc(_RET_IP_, ret,
> > +		      size, s->size,
> > +		      flags, node);
> >  	return ret;
> >  }
> >  
> > @@ -1075,8 +1076,9 @@ void *kmalloc_large(size_t size, gfp_t flags)
> >  {
> >  	void *ret = __kmalloc_large_node_notrace(size, flags, NUMA_NO_NODE);
> >  
> > -	trace_kmalloc(_RET_IP_, ret, NULL, size,
> > -		      PAGE_SIZE << get_order(size), flags, NUMA_NO_NODE);
> > +	trace_kmalloc(_RET_IP_, ret,
> > +		      size, PAGE_SIZE << get_order(size),
> > +		      flags, NUMA_NO_NODE);
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(kmalloc_large);
> > @@ -1090,8 +1092,9 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node)
> >  {
> >  	void *ret = __kmalloc_large_node_notrace(size, flags, node);
> >  
> > -	trace_kmalloc(_RET_IP_, ret, NULL, size,
> > -		      PAGE_SIZE << get_order(size), flags, node);
> > +	trace_kmalloc(_RET_IP_, ret,
> > +		      size, PAGE_SIZE << get_order(size),
> > +		      flags, node);
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(kmalloc_large_node);
> > diff --git a/mm/slob.c b/mm/slob.c
> > index a4d50d957c25..97a4d2407f96 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -507,8 +507,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> >  		*m = size;
> >  		ret = (void *)m + minalign;
> >  
> > -		trace_kmalloc(caller, ret, NULL,
> > -			      size, size + minalign, gfp, node);
> > +		trace_kmalloc(caller, ret, size, size + minalign, gfp, node);
> >  	} else {
> >  		unsigned int order = get_order(size);
> >  
> > @@ -516,8 +515,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> >  			gfp |= __GFP_COMP;
> >  		ret = slob_new_pages(gfp, order, node);
> >  
> > -		trace_kmalloc(caller, ret, NULL,
> > -			      size, PAGE_SIZE << order, gfp, node);
> > +		trace_kmalloc(caller, ret, size, PAGE_SIZE << order, gfp, node);
> >  	}
> >  
> >  	kmemleak_alloc(ret, size, 1, gfp);
> > @@ -608,14 +606,10 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
> >  
> >  	if (c->size < PAGE_SIZE) {
> >  		b = slob_alloc(c->size, flags, c->align, node, 0);
> > -		trace_kmem_cache_alloc(_RET_IP_, b, NULL, c->object_size,
> > -				       SLOB_UNITS(c->size) * SLOB_UNIT,
> 
> Hm we lose the SLOB_UNITS() adjustment here.

Thank you for catching this.

> Maybe we don't care that much,
> maybe simply c->size could be already stored with SLOB_UNITS() (but didn't
> check if other stuff breaks with that).

Hmm will try that way!

Thanks!

> 
> Thanks!
> 
> > -				       flags, node);
> > +		trace_kmem_cache_alloc(_RET_IP_, b, c, flags, node);
> >  	} else {
> >  		b = slob_new_pages(flags, get_order(c->size), node);
> > -		trace_kmem_cache_alloc(_RET_IP_, b, NULL, c->object_size,
> > -				       PAGE_SIZE << get_order(c->size),
> > -				       flags, node);
> > +		trace_kmem_cache_alloc(_RET_IP_, b, c, flags, node);
> >  	}
> >  
> >  	if (b && c->ctor) {
> > @@ -671,7 +665,7 @@ static void kmem_rcu_free(struct rcu_head *head)
> >  void kmem_cache_free(struct kmem_cache *c, void *b)
> >  {
> >  	kmemleak_free_recursive(b, c->flags);
> > -	trace_kmem_cache_free(_RET_IP_, b, c->name);
> > +	trace_kmem_cache_free(_RET_IP_, b, c);
> >  	if (unlikely(c->flags & SLAB_TYPESAFE_BY_RCU)) {
> >  		struct slob_rcu *slob_rcu;
> >  		slob_rcu = b + (c->size - sizeof(struct slob_rcu));
> > diff --git a/mm/slub.c b/mm/slub.c
> > index f1aa51480dc4..a49c69469c64 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -3243,8 +3243,7 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> >  {
> >  	void *ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> >  
> > -	trace_kmem_cache_alloc(_RET_IP_, ret, s, s->object_size,
> > -				s->size, gfpflags, NUMA_NO_NODE);
> > +	trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, NUMA_NO_NODE);
> >  
> >  	return ret;
> >  }
> > @@ -3274,7 +3273,7 @@ void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags,
> >  void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
> >  {
> >  	void *ret = slab_alloc(s, NULL, gfpflags, _RET_IP_, size);
> > -	trace_kmalloc(_RET_IP_, ret, s, size, s->size, gfpflags, NUMA_NO_NODE);
> > +	trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags, NUMA_NO_NODE);
> >  	ret = kasan_kmalloc(s, ret, size, gfpflags);
> >  	return ret;
> >  }
> > @@ -3285,8 +3284,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, int node)
> >  {
> >  	void *ret = slab_alloc_node(s, NULL, gfpflags, node, _RET_IP_, s->object_size);
> >  
> > -	trace_kmem_cache_alloc(_RET_IP_, ret, s,
> > -			       s->object_size, s->size, gfpflags, node);
> > +	trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, node);
> >  
> >  	return ret;
> >  }
> > @@ -3299,8 +3297,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
> >  {
> >  	void *ret = slab_alloc_node(s, NULL, gfpflags, node, _RET_IP_, size);
> >  
> > -	trace_kmalloc(_RET_IP_, ret, s,
> > -		      size, s->size, gfpflags, node);
> > +	trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags, node);
> >  
> >  	ret = kasan_kmalloc(s, ret, size, gfpflags);
> >  	return ret;
> > @@ -3544,7 +3541,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
> >  	s = cache_from_obj(s, x);
> >  	if (!s)
> >  		return;
> > -	trace_kmem_cache_free(_RET_IP_, x, s->name);
> > +	trace_kmem_cache_free(_RET_IP_, x, s);
> >  	slab_free(s, virt_to_slab(x), x, NULL, &x, 1, _RET_IP_);
> >  }
> >  EXPORT_SYMBOL(kmem_cache_free);
> 

-- 
Thanks,
Hyeonggon