linux-kernel - Re: [PATCH] block,blkcg: use __GFP_NOWARN for best-effort allocations in blkcg

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Date:   Tue, 22 Nov 2016 16:47:49 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Marc MERLIN <marc@...lins.org>
Subject: Re: [PATCH] block,blkcg: use __GFP_NOWARN for best-effort allocations
 in blkcg

On 11/22/2016 12:03 AM, Tejun Heo wrote:
> blkcg allocates some per-cgroup data structures with GFP_NOWAIT and
> when that fails falls back to operations which aren't specific to the
> cgroup.  Occassional failures are expected under pressure and falling
> back to non-cgroup operation is the right thing to do.
> 
> Unfortunately, I forgot to add __GFP_NOWARN to these allocations and
> these expected failures end up creating a lot of noise.  Add
> __GFP_NOWARN.

Thanks. Makes me wonder whether we should e.g. add __GFP_NOWARN to
GFP_NOWAIT globally at some point.

> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Marc MERLIN <marc@...lins.org>
> Reported-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  block/blk-cgroup.c  |    9 +++++----
>  block/cfq-iosched.c |    3 ++-
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index b08ccbb..8ba0af7 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -185,7 +185,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
>  	}
>  
>  	wb_congested = wb_congested_get_create(&q->backing_dev_info,
> -					       blkcg->css.id, GFP_NOWAIT);
> +					       blkcg->css.id,
> +					       GFP_NOWAIT | __GFP_NOWARN);
>  	if (!wb_congested) {
>  		ret = -ENOMEM;
>  		goto err_put_css;
> @@ -193,7 +194,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
>  
>  	/* allocate */
>  	if (!new_blkg) {
> -		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT);
> +		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
>  		if (unlikely(!new_blkg)) {
>  			ret = -ENOMEM;
>  			goto err_put_congested;
> @@ -1022,7 +1023,7 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
>  	}
>  
>  	spin_lock_init(&blkcg->lock);
> -	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT);
> +	INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_NOWAIT | __GFP_NOWARN);
>  	INIT_HLIST_HEAD(&blkcg->blkg_list);
>  #ifdef CONFIG_CGROUP_WRITEBACK
>  	INIT_LIST_HEAD(&blkcg->cgwb_list);
> @@ -1240,7 +1241,7 @@ int blkcg_activate_policy(struct request_queue *q,
>  		if (blkg->pd[pol->plid])
>  			continue;
>  
> -		pd = pol->pd_alloc_fn(GFP_NOWAIT, q->node);
> +		pd = pol->pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN, q->node);
>  		if (!pd)
>  			swap(pd, pd_prealloc);
>  		if (!pd) {
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 5e24d88..b4c3b6c 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -3854,7 +3854,8 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
>  			goto out;
>  	}
>  
> -	cfqq = kmem_cache_alloc_node(cfq_pool, GFP_NOWAIT | __GFP_ZERO,
> +	cfqq = kmem_cache_alloc_node(cfq_pool,
> +				     GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
>  				     cfqd->queue->node);
>  	if (!cfqq) {
>  		cfqq = &cfqd->oom_cfqq;
>