Re: [PATCH v3 1/3] mm, memcg: add mem_cgroup_disabled checks in vmpressure and swap-related functions

[Miaohe Lin]

On 2021/7/10 8:36, Suren Baghdasaryan wrote:
> Add mem_cgroup_disabled check in vmpressure, mem_cgroup_uncharge_swap and
> cgroup_throttle_swaprate functions. This minimizes the memcg overhead in
> the pagefault and exit_mmap paths when memcgs are disabled using
> cgroup_disable=memory command-line option.
> This change results in ~2.1% overhead reduction when running PFT test
> comparing {CONFIG_MEMCG=n, CONFIG_MEMCG_SWAP=n} against {CONFIG_MEMCG=y,
> CONFIG_MEMCG_SWAP=y, cgroup_disable=memory} configuration on an 8-core
> ARM64 Android device.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
>  mm/memcontrol.c | 3 +++
>  mm/swapfile.c   | 3 +++
>  mm/vmpressure.c | 7 ++++++-
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ae1f5d0cb581..a228cd51c4bd 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7305,6 +7305,9 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
>  	struct mem_cgroup *memcg;
>  	unsigned short id;
>  
> +	if (mem_cgroup_disabled())
> +		return;
> +
>  	id = swap_cgroup_record(entry, 0, nr_pages);
>  	rcu_read_lock();
>  	memcg = mem_cgroup_from_id(id);
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 1e07d1c776f2..707fa0481bb4 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3778,6 +3778,9 @@ void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
>  	struct swap_info_struct *si, *next;
>  	int nid = page_to_nid(page);
>  
> +	if (mem_cgroup_disabled())
> +		return;
> +

Many thanks for your patch. But I'am somewhat confused about this change.
IMO, cgroup_throttle_swaprate() is only related to blk_cgroup and it seems
it's irrelevant to mem_cgroup. Could you please have a explanation for me?

Thanks!

>  	if (!(gfp_mask & __GFP_IO))
>  		return;
>  
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index d69019fc3789..9b172561fded 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -240,7 +240,12 @@ static void vmpressure_work_fn(struct work_struct *work)
>  void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>  		unsigned long scanned, unsigned long reclaimed)
>  {
> -	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
> +	struct vmpressure *vmpr;
> +
> +	if (mem_cgroup_disabled())
> +		return;
> +
> +	vmpr = memcg_to_vmpressure(memcg);
>  
>  	/*
>  	 * Here we only want to account pressure that userland is able to
>