Commit 5e1f0f09 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm, compaction: capture a page under direct compaction 

Compaction is inherently race-prone as a suitable page freed during
compaction can be allocated by any parallel task.  This patch uses a
capture_control structure to isolate a page immediately when it is freed
by a direct compactor in the slow path of the page allocator.  The
intent is to avoid redundant scanning.

                                     5.0.0-rc1              5.0.0-rc1
                               selective-v3r17          capture-v3r19
Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
Amean     fault-both-3      2582.11 (   0.00%)     2563.68 (   0.71%)
Amean     fault-both-5      4500.26 (   0.00%)     4233.52 (   5.93%)
Amean     fault-both-7      5819.53 (   0.00%)     6333.65 (  -8.83%)
Amean     fault-both-12     9321.18 (   0.00%)     9759.38 (  -4.70%)
Amean     fault-both-18     9782.76 (   0.00%)    10338.76 (  -5.68%)
Amean     fault-both-24    15272.81 (   0.00%)    13379.55 *  12.40%*
Amean     fault-both-30    15121.34 (   0.00%)    16158.25 (  -6.86%)
Amean     fault-both-32    18466.67 (   0.00%)    18971.21 (  -2.73%)

Latency is only moderately affected but the devil is in the details.  A
closer examination indicates that base page fault latency is reduced but
latency of huge pages is increased as it takes creater care to succeed.
Part of the "problem" is that allocation success rates are close to 100%
even when under pressure and compaction gets harder

                                5.0.0-rc1              5.0.0-rc1
                          selective-v3r17          capture-v3r19
Percentage huge-3        96.70 (   0.00%)       98.23 (   1.58%)
Percentage huge-5        96.99 (   0.00%)       95.30 (  -1.75%)
Percentage huge-7        94.19 (   0.00%)       97.24 (   3.24%)
Percentage huge-12       94.95 (   0.00%)       97.35 (   2.53%)
Percentage huge-18       96.74 (   0.00%)       97.30 (   0.58%)
Percentage huge-24       97.07 (   0.00%)       97.55 (   0.50%)
Percentage huge-30       95.69 (   0.00%)       98.50 (   2.95%)
Percentage huge-32       96.70 (   0.00%)       99.27 (   2.65%)

And scan rates are reduced as expected by 6% for the migration scanner
and 29% for the free scanner indicating that there is less redundant
work.

Compaction migrate scanned    20815362    19573286
Compaction free scanned       16352612    11510663

[mgorman@techsingularity.net: remove redundant check]
  Link: http://lkml.kernel.org/r/20190201143853.GH9565@techsingularity.net
Link: http://lkml.kernel.org/r/20190118175136.31341-23-mgorman@techsingularity.net


Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e332f741

include/linux/compaction.h

+2 −1
Original line number Diff line number Diff line
@@ -93,7 +93,8 @@ extern int sysctl_compact_unevictable_allowed; 
extern int fragmentation_index(struct zone *zone, unsigned int order);

extern enum compact_result try_to_compact_pages(gfp_t gfp_mask,

		unsigned int order, unsigned int alloc_flags,

		const struct alloc_context *ac, enum compact_priority prio);

		const struct alloc_context *ac, enum compact_priority prio,

		struct page **page);

extern void reset_isolation_suitable(pg_data_t *pgdat);

extern enum compact_result compaction_suitable(struct zone *zone, int order,

		unsigned int alloc_flags, int classzone_idx);

include/linux/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ struct pid_namespace; 
struct pipe_inode_info;

struct rcu_node;

struct reclaim_state;

struct capture_control;

struct robust_list_head;

struct sched_attr;

struct sched_param;
@@ -958,6 +959,9 @@ struct task_struct { 


	struct io_context		*io_context;



#ifdef CONFIG_COMPACTION

	struct capture_control		*capture_control;

#endif

	/* Ptrace state: */

	unsigned long			ptrace_message;

	kernel_siginfo_t		*last_siginfo;

kernel/sched/core.c

+3 −0
Original line number Diff line number Diff line
@@ -2190,6 +2190,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) 
	INIT_HLIST_HEAD(&p->preempt_notifiers);

#endif



#ifdef CONFIG_COMPACTION

	p->capture_control = NULL;

#endif

	init_numa_balancing(clone_flags, p);

}

mm/compaction.c

+24 −7
Original line number Diff line number Diff line
@@ -2056,7 +2056,8 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order, 
	return false;

}



static enum compact_result compact_zone(struct compact_control *cc)

static enum compact_result

compact_zone(struct compact_control *cc, struct capture_control *capc)

{

	enum compact_result ret;

	unsigned long start_pfn = cc->zone->zone_start_pfn;
@@ -2225,6 +2226,11 @@ check_drain: 
			}

		}



		/* Stop if a page has been captured */

		if (capc && capc->page) {

			ret = COMPACT_SUCCESS;

			break;

		}

	}



out:
@@ -2258,7 +2264,8 @@ out: 


static enum compact_result compact_zone_order(struct zone *zone, int order,

		gfp_t gfp_mask, enum compact_priority prio,

		unsigned int alloc_flags, int classzone_idx)

		unsigned int alloc_flags, int classzone_idx,

		struct page **capture)

{

	enum compact_result ret;

	struct compact_control cc = {
@@ -2279,14 +2286,24 @@ static enum compact_result compact_zone_order(struct zone *zone, int order, 
		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),

		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)

	};

	struct capture_control capc = {

		.cc = &cc,

		.page = NULL,

	};



	if (capture)

		current->capture_control = &capc;

	INIT_LIST_HEAD(&cc.freepages);

	INIT_LIST_HEAD(&cc.migratepages);



	ret = compact_zone(&cc);

	ret = compact_zone(&cc, &capc);



	VM_BUG_ON(!list_empty(&cc.freepages));

	VM_BUG_ON(!list_empty(&cc.migratepages));



	*capture = capc.page;

	current->capture_control = NULL;



	return ret;

}
@@ -2304,7 +2321,7 @@ int sysctl_extfrag_threshold = 500; 
 */

enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,

		unsigned int alloc_flags, const struct alloc_context *ac,

		enum compact_priority prio)

		enum compact_priority prio, struct page **capture)

{

	int may_perform_io = gfp_mask & __GFP_IO;

	struct zoneref *z;
@@ -2332,7 +2349,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order, 
		}



		status = compact_zone_order(zone, order, gfp_mask, prio,

					alloc_flags, ac_classzone_idx(ac));

				alloc_flags, ac_classzone_idx(ac), capture);

		rc = max(status, rc);



		/* The allocation should succeed, stop compacting */
@@ -2400,7 +2417,7 @@ static void compact_node(int nid) 
		INIT_LIST_HEAD(&cc.freepages);

		INIT_LIST_HEAD(&cc.migratepages);



		compact_zone(&cc);

		compact_zone(&cc, NULL);



		VM_BUG_ON(!list_empty(&cc.freepages));

		VM_BUG_ON(!list_empty(&cc.migratepages));
@@ -2535,7 +2552,7 @@ static void kcompactd_do_work(pg_data_t *pgdat) 


		if (kthread_should_stop())

			return;

		status = compact_zone(&cc);

		status = compact_zone(&cc, NULL);



		if (status == COMPACT_SUCCESS) {

			compaction_defer_reset(zone, cc.order, false);

mm/internal.h

+9 −0
Original line number Diff line number Diff line
@@ -209,6 +209,15 @@ struct compact_control { 
	bool rescan;			/* Rescanning the same pageblock */

};



/*

 * Used in direct compaction when a page should be taken from the freelists

 * immediately when one is created during the free path.

 */

struct capture_control {

	struct compact_control *cc;

	struct page *page;

};



unsigned long

isolate_freepages_range(struct compact_control *cc,

			unsigned long start_pfn, unsigned long end_pfn);

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