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Commit d9bfcfdc authored by Huang Ying's avatar Huang Ying Committed by Linus Torvalds
Browse files

mm, swap: add sysfs interface for VMA based swap readahead 

The sysfs interface to control the VMA based swap readahead is added as
follow,

/sys/kernel/mm/swap/vma_ra_enabled

Enable the VMA based swap readahead algorithm, or use the original
global swap readahead algorithm.

/sys/kernel/mm/swap/vma_ra_max_order

Set the max order of the readahead window size for the VMA based swap
readahead algorithm.

The corresponding ABI documentation is added too.

Link: http://lkml.kernel.org/r/20170807054038.1843-5-ying.huang@intel.com


Signed-off-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ec560175

Documentation/ABI/testing/sysfs-kernel-mm-swap

0 → 100644
+26 −0
Original line number Diff line number Diff line 
What:		/sys/kernel/mm/swap/

Date:		August 2017

Contact:	Linux memory management mailing list <linux-mm@kvack.org>

Description:	Interface for swapping



What:		/sys/kernel/mm/swap/vma_ra_enabled

Date:		August 2017

Contact:	Linux memory management mailing list <linux-mm@kvack.org>

Description:	Enable/disable VMA based swap readahead.



		If set to true, the VMA based swap readahead algorithm

		will be used for swappable anonymous pages mapped in a

		VMA, and the global swap readahead algorithm will be

		still used for tmpfs etc. other users.  If set to

		false, the global swap readahead algorithm will be

		used for all swappable pages.



What:		/sys/kernel/mm/swap/vma_ra_max_order

Date:		August 2017

Contact:	Linux memory management mailing list <linux-mm@kvack.org>

Description:	The max readahead size in order for VMA based swap readahead



		VMA based swap readahead algorithm will readahead at

		most 1 << max_order pages for each readahead.  The

		real readahead size for each readahead will be scaled

		according to the estimation algorithm.

mm/swap_state.c

+80 −0
Original line number Diff line number Diff line
@@ -751,3 +751,83 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask, 
	return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,

				     swap_ra->win == 1);

}



#ifdef CONFIG_SYSFS

static ssize_t vma_ra_enabled_show(struct kobject *kobj,

				     struct kobj_attribute *attr, char *buf)

{

	return sprintf(buf, "%s\n", swap_vma_readahead ? "true" : "false");

}

static ssize_t vma_ra_enabled_store(struct kobject *kobj,

				      struct kobj_attribute *attr,

				      const char *buf, size_t count)

{

	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))

		swap_vma_readahead = true;

	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))

		swap_vma_readahead = false;

	else

		return -EINVAL;



	return count;

}

static struct kobj_attribute vma_ra_enabled_attr =

	__ATTR(vma_ra_enabled, 0644, vma_ra_enabled_show,

	       vma_ra_enabled_store);



static ssize_t vma_ra_max_order_show(struct kobject *kobj,

				     struct kobj_attribute *attr, char *buf)

{

	return sprintf(buf, "%d\n", swap_ra_max_order);

}

static ssize_t vma_ra_max_order_store(struct kobject *kobj,

				      struct kobj_attribute *attr,

				      const char *buf, size_t count)

{

	int err, v;



	err = kstrtoint(buf, 10, &v);

	if (err || v > SWAP_RA_ORDER_CEILING || v <= 0)

		return -EINVAL;



	swap_ra_max_order = v;



	return count;

}

static struct kobj_attribute vma_ra_max_order_attr =

	__ATTR(vma_ra_max_order, 0644, vma_ra_max_order_show,

	       vma_ra_max_order_store);



static struct attribute *swap_attrs[] = {

	&vma_ra_enabled_attr.attr,

	&vma_ra_max_order_attr.attr,

	NULL,

};



static struct attribute_group swap_attr_group = {

	.attrs = swap_attrs,

};



static int __init swap_init_sysfs(void)

{

	int err;

	struct kobject *swap_kobj;



	swap_kobj = kobject_create_and_add("swap", mm_kobj);

	if (!swap_kobj) {

		pr_err("failed to create swap kobject\n");

		return -ENOMEM;

	}

	err = sysfs_create_group(swap_kobj, &swap_attr_group);

	if (err) {

		pr_err("failed to register swap group\n");

		goto delete_obj;

	}

	return 0;



delete_obj:

	kobject_put(swap_kobj);

	return err;

}

subsys_initcall(swap_init_sysfs);

#endif