Re: [PATCH 4/6] mm: introduce per-node proactive reclaim interface

[Tim Chen <tim.c.chen@linux.intel.com>]

On Fri, 2022-04-15 at 22:39 -0700, Davidlohr Bueso wrote:
> This patch introduces a mechanism to trigger memory reclaim
> as a per-node sysfs interface, inspired by compaction's
> equivalent; ie:
> 
> 	 echo 1G > /sys/devices/system/node/nodeX/reclaim
> 

I think it will be more flexible to specify a node mask
as a parameter along with amount of memory with the 
memory.reclaim memcg interface proposed by Yosry.  Doing it node
by node is more cumbersome.  It is just a special case
of reclaiming from root cgroup for a specific node.

Wei Gu, YIng and I have some discssions on this
https://lore.kernel.org/all/df6110a09cacc80ee1cbe905a71273a5f3953e16.camel@linux.intel.com/  

 
Tim

> It is based on the discussions from David's thread[1] as
> well as the current upstreaming of the memcg[2] interface
> (which has nice explanations for the benefits of userspace
> reclaim overall). In both cases conclusions were that either
> way of inducing proactive reclaim should be KISS, and can be
> later extended. So this patch does not allow the user much
> fine tuning beyond the size of the reclaim, such as anon/file
> or whether or semantics of demotion.
> 
> [1] https://lore.kernel.org/all/5df21376-7dd1-bf81-8414-32a73cea45dd@google.com/
> [2] https://lore.kernel.org/all/20220408045743.1432968-1-yosryahmed@google.com/
> 
> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> ---
>  Documentation/ABI/stable/sysfs-devices-node | 10 ++++
>  drivers/base/node.c                         |  2 +
>  include/linux/swap.h                        | 16 ++++++
>  mm/vmscan.c                                 | 59 +++++++++++++++++++++
>  4 files changed, 87 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index 8db67aa472f1..3c935e1334f7 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -182,3 +182,13 @@ Date:		November 2021
>  Contact:	Jarkko Sakkinen <jarkko@kernel.org>
>  Description:
>  		The total amount of SGX physical memory in bytes.
> +
> +What:		/sys/devices/system/node/nodeX/reclaim
> +Date:		April 2022
> +Contact:	Davidlohr Bueso <dave@stgolabs.net>
> +Description:
> +		Write the amount of bytes to induce memory reclaim in this node.
> +		This file accepts a single key, the number of bytes to reclaim.
> +		When it completes successfully, the specified amount or more memory
> +		will have been reclaimed, and -EAGAIN if less bytes are reclaimed
> +		than the specified amount.
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 6cdf25fd26c3..d80c478e2a6e 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -670,6 +670,7 @@ static int register_node(struct node *node, int num)
>  
>  	hugetlb_register_node(node);
>  	compaction_register_node(node);
> +	reclaim_register_node(node);
>  	return 0;
>  }
>  
> @@ -685,6 +686,7 @@ void unregister_node(struct node *node)
>  	hugetlb_unregister_node(node);		/* no-op, if memoryless node */
>  	node_remove_accesses(node);
>  	node_remove_caches(node);
> +	reclaim_unregister_node(node);
>  	device_unregister(&node->dev);
>  }
>  
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 27093b477c5f..cca43ae6d770 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -398,6 +398,22 @@ extern unsigned long shrink_all_memory(unsigned long nr_pages);
>  extern int vm_swappiness;
>  long remove_mapping(struct address_space *mapping, struct folio *folio);
>  
> +#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> +extern int reclaim_register_node(struct node *node);
> +extern void reclaim_unregister_node(struct node *node);
> +
> +#else
> +
> +static inline int reclaim_register_node(struct node *node)
> +{
> +	return 0;
> +}
> +
> +static inline void reclaim_unregister_node(struct node *node)
> +{
> +}
> +#endif /* CONFIG_SYSFS && CONFIG_NUMA */
> +
>  extern unsigned long reclaim_pages(struct list_head *page_list);
>  #ifdef CONFIG_NUMA
>  extern int node_reclaim_mode;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1735c302831c..3539f8a0f0ea 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4819,3 +4819,62 @@ void check_move_unevictable_pages(struct pagevec *pvec)
>  	}
>  }
>  EXPORT_SYMBOL_GPL(check_move_unevictable_pages);
> +
> +#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> +static ssize_t reclaim_store(struct device *dev,
> +			     struct device_attribute *attr,
> +			     const char *buf, size_t count)
> +{
> +	int err, nid = dev->id;
> +	gfp_t gfp_mask = GFP_KERNEL;
> +	struct pglist_data *pgdat = NODE_DATA(nid);
> +	unsigned long nr_to_reclaim, nr_reclaimed = 0;
> +	unsigned int nr_retries = MAX_RECLAIM_RETRIES;
> +	struct scan_control sc = {
> +		.gfp_mask = current_gfp_context(gfp_mask),
> +		.reclaim_idx = gfp_zone(gfp_mask),
> +		.priority = NODE_RECLAIM_PRIORITY,
> +		.may_writepage = !laptop_mode,
> +		.may_unmap = 1,
> +		.may_swap = 1,
> +	};
> +
> +	buf = strstrip((char *)buf);
> +	err = page_counter_memparse(buf, "", &nr_to_reclaim);
> +	if (err)
> +		return err;
> +
> +	sc.nr_to_reclaim = max(nr_to_reclaim, SWAP_CLUSTER_MAX);
> +
> +	while (nr_reclaimed < nr_to_reclaim) {
> +		unsigned long reclaimed;
> +
> +		if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
> +			return -EAGAIN;
> +
> +		/* does cond_resched() */
> +		reclaimed = __node_reclaim(pgdat, gfp_mask,
> +					   nr_to_reclaim - nr_reclaimed, &sc);
> +
> +		clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
> +
> +		if (!reclaimed && !nr_retries--)
> +			break;
> +
> +		nr_reclaimed += reclaimed;
> +	}
> +
> +	return nr_reclaimed < nr_to_reclaim ? -EAGAIN : count;
> +}
> +
> +static DEVICE_ATTR_WO(reclaim);
> +int reclaim_register_node(struct node *node)
> +{
> +	return device_create_file(&node->dev, &dev_attr_reclaim);
> +}
> +
> +void reclaim_unregister_node(struct node *node)
> +{
> +	return device_remove_file(&node->dev, &dev_attr_reclaim);
> +}
> +#endif