Subject: Re: linux-next: manual merge of the akpm-current tree with the slab tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 17 Dec 2021 23:39:53 +1100

Hi all,

On Fri, 3 Dec 2021 18:19:51 +1100 Stephen Rothwell <[email-masked]> wrote:
>
> Today's linux-next merge of the akpm-current tree got a conflict in:
> 
>   mm/memcontrol.c
> 
> between commit:
> 
>   eefa12e18a92 ("mm/memcg: Convert slab objcgs from struct page to struct slab")
> 
> from the slab tree and commit:
> 
>   93e959c235eb ("mm/memcg: relocate mod_objcg_mlstate(), get_obj_stock() and put_obj_stock()")
> 
> from the akpm-current tree.
> 
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
> 
> diff --cc mm/memcontrol.c
> index 522fff11d6d1,69d4fdafbb80..000000000000
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@@ -2816,10 -2769,63 +2769,63 @@@ retry
>    */
>   #define OBJCGS_CLEAR_MASK	(__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)
>   
> + /*
> +  * Most kmem_cache_alloc() calls are from user context. The irq disable/enable
> +  * sequence used in this case to access content from object stock is slow.
> +  * To optimize for user context access, there are now two object stocks for
> +  * task context and interrupt context access respectively.
> +  *
> +  * The task context object stock can be accessed by disabling preemption only
> +  * which is cheap in non-preempt kernel. The interrupt context object stock
> +  * can only be accessed after disabling interrupt. User context code can
> +  * access interrupt object stock, but not vice versa.
> +  */
> + static inline struct obj_stock *get_obj_stock(unsigned long *pflags)
> + {
> + 	struct memcg_stock_pcp *stock;
> + 
> + 	if (likely(in_task())) {
> + 		*pflags = 0UL;
> + 		preempt_disable();
> + 		stock = this_cpu_ptr(&memcg_stock);
> + 		return &stock->task_obj;
> + 	}
> + 
> + 	local_irq_save(*pflags);
> + 	stock = this_cpu_ptr(&memcg_stock);
> + 	return &stock->irq_obj;
> + }
> + 
> + static inline void put_obj_stock(unsigned long flags)
> + {
> + 	if (likely(in_task()))
> + 		preempt_enable();
> + 	else
> + 		local_irq_restore(flags);
> + }
> + 
> + /*
> +  * mod_objcg_mlstate() may be called with irq enabled, so
> +  * mod_memcg_lruvec_state() should be used.
> +  */
> + static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
> + 				     struct pglist_data *pgdat,
> + 				     enum node_stat_item idx, int nr)
> + {
> + 	struct mem_cgroup *memcg;
> + 	struct lruvec *lruvec;
> + 
> + 	rcu_read_lock();
> + 	memcg = obj_cgroup_memcg(objcg);
> + 	lruvec = mem_cgroup_lruvec(memcg, pgdat);
> + 	mod_memcg_lruvec_state(lruvec, idx, nr);
> + 	rcu_read_unlock();
> + }
> + 
>  -int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
>  -				 gfp_t gfp, bool new_page)
>  +int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
>  +				 gfp_t gfp, bool new_slab)
>   {
>  -	unsigned int objects = objs_per_slab_page(s, page);
>  +	unsigned int objects = objs_per_slab(s, slab);
>   	unsigned long memcg_data;
>   	void *vec;
>   

This is now a conflict between the slab tree and Linus' tree.

-- 
Cheers,
Stephen Rothwell