From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxxx: remove redundant check]
Link: http://lkml.kernel.org/r/20190201143853.GH9565@xxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20190118175136.31341-23-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: YueHaibing <yuehaibing@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/compaction.h | 3 -
include/linux/sched.h | 4 +
kernel/sched/core.c | 3 +
mm/compaction.c | 31 +++++++++++---
mm/internal.h | 9 ++++
mm/page_alloc.c | 73 +++++++++++++++++++++++++++++++++--
6 files changed, 111 insertions(+), 12 deletions(-)
--- a/include/linux/compaction.h~mm-compaction-capture-a-page-under-direct-compaction
+++ a/include/linux/compaction.h
@@ -93,7 +93,8 @@ extern int sysctl_compact_unevictable_al
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);
--- a/include/linux/sched.h~mm-compaction-capture-a-page-under-direct-compaction
+++ a/include/linux/sched.h
@@ -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;
--- a/kernel/sched/core.c~mm-compaction-capture-a-page-under-direct-compaction
+++ a/kernel/sched/core.c
@@ -2190,6 +2190,9 @@ static void __sched_fork(unsigned long c
INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif
+#ifdef CONFIG_COMPACTION
+ p->capture_control = NULL;
+#endif
init_numa_balancing(clone_flags, p);
}
--- a/mm/compaction.c~mm-compaction-capture-a-page-under-direct-compaction
+++ a/mm/compaction.c
@@ -2056,7 +2056,8 @@ bool compaction_zonelist_suitable(struct
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_
.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
}
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
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);
--- a/mm/internal.h~mm-compaction-capture-a-page-under-direct-compaction
+++ a/mm/internal.h
@@ -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);
--- a/mm/page_alloc.c~mm-compaction-capture-a-page-under-direct-compaction
+++ a/mm/page_alloc.c
@@ -789,6 +789,57 @@ static inline int page_is_buddy(struct p
return 0;
}
+#ifdef CONFIG_COMPACTION
+static inline struct capture_control *task_capc(struct zone *zone)
+{
+ struct capture_control *capc = current->capture_control;
+
+ return capc &&
+ !(current->flags & PF_KTHREAD) &&
+ !capc->page &&
+ capc->cc->zone == zone &&
+ capc->cc->direct_compaction ? capc : NULL;
+}
+
+static inline bool
+compaction_capture(struct capture_control *capc, struct page *page,
+ int order, int migratetype)
+{
+ if (!capc || order != capc->cc->order)
+ return false;
+
+ /* Do not accidentally pollute CMA or isolated regions*/
+ if (is_migrate_cma(migratetype) ||
+ is_migrate_isolate(migratetype))
+ return false;
+
+ /*
+ * Do not let lower order allocations polluate a movable pageblock.
+ * This might let an unmovable request use a reclaimable pageblock
+ * and vice-versa but no more than normal fallback logic which can
+ * have trouble finding a high-order free page.
+ */
+ if (order < pageblock_order && migratetype == MIGRATE_MOVABLE)
+ return false;
+
+ capc->page = page;
+ return true;
+}
+
+#else
+static inline struct capture_control *task_capc(struct zone *zone)
+{
+ return NULL;
+}
+
+static inline bool
+compaction_capture(struct capture_control *capc, struct page *page,
+ int order, int migratetype)
+{
+ return false;
+}
+#endif /* CONFIG_COMPACTION */
+
/*
* Freeing function for a buddy system allocator.
*
@@ -822,6 +873,7 @@ static inline void __free_one_page(struc
unsigned long uninitialized_var(buddy_pfn);
struct page *buddy;
unsigned int max_order;
+ struct capture_control *capc = task_capc(zone);
max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
@@ -837,6 +889,11 @@ static inline void __free_one_page(struc
continue_merging:
while (order < max_order - 1) {
+ if (compaction_capture(capc, page, order, migratetype)) {
+ __mod_zone_freepage_state(zone, -(1 << order),
+ migratetype);
+ return;
+ }
buddy_pfn = __find_buddy_pfn(pfn, order);
buddy = page + (buddy_pfn - pfn);
@@ -3710,7 +3767,7 @@ __alloc_pages_direct_compact(gfp_t gfp_m
unsigned int alloc_flags, const struct alloc_context *ac,
enum compact_priority prio, enum compact_result *compact_result)
{
- struct page *page;
+ struct page *page = NULL;
unsigned long pflags;
unsigned int noreclaim_flag;
@@ -3721,13 +3778,15 @@ __alloc_pages_direct_compact(gfp_t gfp_m
noreclaim_flag = memalloc_noreclaim_save();
*compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
- prio);
+ prio, &page);
memalloc_noreclaim_restore(noreclaim_flag);
psi_memstall_leave(&pflags);
- if (*compact_result <= COMPACT_INACTIVE)
+ if (*compact_result <= COMPACT_INACTIVE) {
+ WARN_ON_ONCE(page);
return NULL;
+ }
/*
* At least in one zone compaction wasn't deferred or skipped, so let's
@@ -3735,7 +3794,13 @@ __alloc_pages_direct_compact(gfp_t gfp_m
*/
count_vm_event(COMPACTSTALL);
- page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
+ /* Prep a captured page if available */
+ if (page)
+ prep_new_page(page, order, gfp_mask, alloc_flags);
+
+ /* Try get a page from the freelist if available */
+ if (!page)
+ page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
if (page) {
struct zone *zone = page_zone(page);
_
