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Message-ID: <BYAPR12MB3015778A34F153B43B52CFDED8E50@BYAPR12MB3015.namprd12.prod.outlook.com>
Date: Wed, 4 Mar 2020 23:13:39 +0000
From: Nitin Gupta <nigupta@...dia.com>
To: Vlastimil Babka <vbabka@...e.cz>,
Mel Gorman <mgorman@...hsingularity.net>,
Michal Hocko <mhocko@...e.com>
CC: Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>,
Linux API <linux-api@...r.kernel.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
David Rientjes <rientjes@...gle.com>
Subject: RE: [PATCH v2] mm: Proactive compaction
> -----Original Message-----
> From: Vlastimil Babka <vbabka@...e.cz>
> Sent: Wednesday, March 4, 2020 10:04 AM
> To: Nitin Gupta <nigupta@...dia.com>; Mel Gorman
> <mgorman@...hsingularity.net>; Michal Hocko <mhocko@...e.com>
> Cc: Matthew Wilcox <willy@...radead.org>; Andrew Morton <akpm@...ux-
> foundation.org>; Mike Kravetz <mike.kravetz@...cle.com>; linux-kernel <linux-
> kernel@...r.kernel.org>; linux-mm <linux-mm@...ck.org>; Linux API <linux-
> api@...r.kernel.org>; Joonsoo Kim <iamjoonsoo.kim@....com>; David Rientjes
> <rientjes@...gle.com>
> Subject: Re: [PATCH v2] mm: Proactive compaction
>
> +CC linux-api (new tunable) and more folks who have discussed compaction
> +before
>
> On 3/2/20 10:33 PM, Nitin Gupta wrote:
> > For some applications we need to allocate almost all memory as
> > hugepages. However, on a running system, higher order allocations can
> > fail if the memory is fragmented. Linux kernel currently does
> > on-demand compaction as we request more hugepages but this style of
> > compaction incurs very high latency. Experiments with one-time full
> > memory compaction (followed by hugepage allocations) shows that kernel
> > is able to restore a highly fragmented memory state to a fairly
> > compacted memory state within <1 sec for a 32G system. Such data
> > suggests that a more proactive compaction can help us allocate a large
> > fraction of memory as hugepages keeping allocation latencies low.
>
> Yeah, we should have something like this, currently kcompactd does only very
> limited work.
>
> > For a more proactive compaction, the approach taken here is to define
> > per page-node tunable called 'proactiveness' which dictates bounds for
> > external fragmentation for HUGETLB_PAGE_ORDER pages which kcompactd
> > should try to maintain.
> >
> > The tunable is exposed through sysfs:
> > /sys/kernel/mm/compaction/node-n/proactiveness
> >
> > The value of this tunable is used to determine low and high thresholds
> > for external fragmentation wrt HUGETLB_PAGE_ORDER order.
> >
> > Note that previous version of this patch [1] was found to introduce
> > too many tunables (per-order extfrag{low, high}) but this one reduces
> > them to just (per-node proactiveness). Also, the new tunable is an
> > opaque value instead of asking for specific bounds of "external
> > fragmentation" which would have been difficult to estimate. The
> > internal interpretation of this opaque value allows for future fine-tuning.
>
> I guess we can live with that single tunable, like we have swappiness. The per-
> order thresholds would be too much indeed. But does it have to be per-node?
> Wouldn't a single one be enough?
>
I don't have a strong reason for having per-node tunable except for maybe giving
userspace some more control over compaction process. Maybe we can just
have a single tunable (i.e. not per-node but global) and use some heuristics
internally to balance compaction effort across nodes. I will post a v3 with this
change.
> > Currently, we use a simple translation from this tunable to [low,
> > high] "proactive compaction score" thresholds (low=100-proactiveness,
> > high=low+10%). The score for a node is defined as weighed mean of
> > per-zone external fragmentation wrt HUGETLB_PAGE_ORDER. A zone's
> > present_pages determines its weight. Proactive compaction is triggered
> > when a node's score exceeds its high threshold value and continues
> > till it reaches its low value.
> >
> > To periodically check per-node score, we reuse per-node kcompactd
> > threads which are woken up every few milliseconds to check the same.
> > If
>
> Few milliseconds would be excessive. The code seems to define that as 500,
> which is somewhat better. Should there be also a backoff though if it finds out it
> has nothing to do? And perhaps if kswapd is running on the node, kcompactd
> should wait so they don't interfere?
>
I think backoff should be done only when there is a need for proactive compaction
but it could not make forward progress. Backoff simply because at the time of
score calculation it happened to be lower than threshold doesn't seem right.
Otherwise, backing off when kswapd is active sounds good to me.
> > a node's score exceeds its high threshold (as derived from user
> > provided proactiveness value), proactive compaction is started till
> > its score reaches its low threshold value. By default, proactiveness
> > is set to 0 (=> low=100%, high=100%) for all nodes.
>
> Maybe we can go with a non-0 yet conservative default after some more
> testing.
Hmm... my testing shows proactiveness=20 as a good, conservative default.
I will post more numbers with different proactiveness values for different
workloads.
>
> > This patch is largely based on ideas from Michal Hocko posted here:
> > https://lore.kernel.org/linux-mm/20161230131412.GI13301@dhcp22.suse.cz
> > /
> >
> > Performance data
> > ================
> >
> > System: x64_64, 1T RAM, 80 CPU threads.
> > Kernel: 5.6.0-rc3 + this patch
> >
> > echo madvise | sudo tee /sys/kernel/mm/transparent_hugepage/enabled
> > echo madvise | sudo tee /sys/kernel/mm/transparent_hugepage/defrag
> >
> > Before starting the driver, the system was fragmented from a userspace
> > program that allocates all memory and then for each 2M aligned
> > section, frees 3/4 of base pages using munmap. The workload is mainly
> > anonymous userspace pages which are easy to move around. I
> > intentionally avoided unmovable pages in this test to see how much
> > latency we incur when hugepage allocations hit direct compaction.
> >
> > 1. Kernel hugepage allocation latencies
> >
> > With system in such a fragmented state, a kernel driver then allocates
> > as many hugepages as possible and measures allocation latency:
> >
> > (all latency values are in microseconds)
> >
> > - With vanilla 5.6.0-rc3
> >
> > echo 0 | sudo tee /sys/kernel/mm/compaction/node-*/proactiveness
> >
> > percentile latency
> > –––––––––– –––––––
> > 5 7894
> > 10 9496
> > 25 12561
> > 30 15295
> > 40 18244
> > 50 21229
> > 60 27556
> > 75 30147
> > 80 31047
> > 90 32859
> > 95 33799
> >
> > Total 2M hugepages allocated = 383859 (749G worth of hugepages out of
> > 762G total free => 98% of free memory could be allocated as hugepages)
> >
> > - With 5.6.0-rc3 + this patch, with proactiveness=20
> >
> > echo 20 | sudo tee /sys/kernel/mm/compaction/node-*/proactiveness
> >
> > percentile latency
> > –––––––––– –––––––
> > 5 2
> > 10 2
> > 25 3
> > 30 3
> > 40 3
> > 50 4
> > 60 4
> > 75 4
> > 80 4
> > 90 5
> > 95 429
> >
> > Total 2M hugepages allocated = 11120 (21.7G worth of hugepages out of
> > 25G total free => 98% of free memory could be allocated as hugepages)
>
> By your description it seems to be a one-time fragmentation event followed by a
> one-time stream of allocations? So kcompactd probably did the proactive work
> just once? That works as a smoke test, but what I guess will be more important
> is behavior under more complex workloads, where we should also check the
> vmstat
> compact_daemon* stats and possibly also kcompactd kthreads CPU utilizations.
>
No, proactive compaction happens throughout the duration of these benchmarks.
The situation of one-time compaction, sufficient to supply hugepages for following
allocation stream can probably happen for more extreme values, like 80 or 90. That
is why I chose a smaller value like 20 to make sure proactive compaction goes on in
parallel with allocating program for more realistic numbers.
To verify that compaction indeed happens during benchmarks, I used a simple bpftrace
script:
kprobe:proactive_compact_node {
@[func] = count();
}
This bpftrace is active before letting this test kernel module allocate hugepages and is
terminated once the module hits allocation failure (and thus stops any further allocations).
The script shows that proactive_compact_node() was called 6 times during ~1min runtime
of this test kernel module.
> > 2. JAVA heap allocation
> >
> > First fragment memory using the same method as for (1).
> >
> > With memory in a fragmented state, run:
> >
> > /usr/bin/time
> > java -Xms700G -Xmx700G -XX:+UseTransparentHugePages
> > -XX:+AlwaysPreTouch
> >
> > To allocate 700G of java heap using hugepages.
> >
> > - With vanilla 5.6.0-rc3
> >
> > 17.39user 1666.48system 27:37.89elapsed
> >
> > - With 5.6.0-rc3 + this patch, with proactiveness=20
> >
> > 8.35user 194.58system 3:19.62elapsed
> >
> > Elapsed time remains around 3:15 as proactiveness is further increased.
>
> Similar comment as for the above test. But that's a large reduction, so I wonder
> how much time kcompactd took for this defragmentation. Was there a
> comparably large delay between the fragmentation and the java application to
> let kcompactd do the job? Or was it that much more efficient than the one-
> compaction-per-single-hugepage that the java page faulting caused?
>
> >
The only delay between fragmentation and running this java benchmark is the
time I took to switch between terminals. Anyways, using the same bpftrace,
I see that proactive_compact_node was invoked 21 times during the ~3:15 minute
run of this java benchmark.
This is what happens during any of these benchmarks: with proactiveness=20,
the test starts with extfrag (wrt hugepage order) of ~80% (or higher, depending on
delay in starting the benchmark). As benchmark consumes hugepages,
extfrag (percentage of free memory not available as hugepages) quickly rises and
proactive compaction starts again which (hopefully) brings down extfrag levels.
Repeat.
Thanks,
Nitin
> > Backoff behavior
> > ================
> >
> > Above workloads produces a memory state which is easy to compact.
> > However, if memory is filled with unmovable pages, proactive
> > compaction should essentially back off. To test this aspect:
> >
> > - Created a kernel driver that allocates almost all memory as hugepages
> > followed by freeing first 3/4 of each hugepage.
> > - Set proactiveness=40 (for all nodes)
> > - Note that proactive_compact_node() is deferred maximum number of times
> > with HPAGE_FRAG_CHECK_INTERVAL_MSEC of wait between each check
> > (=> ~30 seconds between retries).
> >
> > [1] https://patchwork.kernel.org/patch/11098289/
> >
> > Signed-off-by: Nitin Gupta <nigupta@...dia.com>
> > To: Mel Gorman <mgorman@...hsingularity.net>
> > To: Michal Hocko <mhocko@...e.com>
> > To: Vlastimil Babka <vbabka@...e.cz>
> > CC: Matthew Wilcox <willy@...radead.org>
> > CC: Andrew Morton <akpm@...ux-foundation.org>
> > CC: Mike Kravetz <mike.kravetz@...cle.com>
> > CC: linux-kernel <linux-kernel@...r.kernel.org>
> > CC: linux-mm <linux-mm@...ck.org>
>
> I haven't studied the code in detail yet, but leaving the mail for the reference of
> new CC's.
>
> Thanks,
> Vlastimil
>
> > ---
> > Changelog v2 vs v1:
> > - Introduce per-node and per-zone "proactive compaction score". This
> > score is compared against watermarks which are set according to
> > user provided proactiveness value.
> > - Separate code-paths for proactive compaction from targeted compaction
> > i.e. where pgdat->kcompactd_max_order is non-zero.
> > - Renamed hpage_compaction_effort -> proactiveness. In future we may
> > use more than extfrag wrt hugepage size to determine proactive
> > compaction score.
> > ---
> > include/linux/compaction.h | 10 ++
> > mm/compaction.c | 242 ++++++++++++++++++++++++++++++++++++-
> > mm/internal.h | 1 +
> > mm/page_alloc.c | 1 +
> > mm/vmstat.c | 12 ++
> > 5 files changed, 260 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> > index 4b898cdbdf05..c98f45107164 100644
> > --- a/include/linux/compaction.h
> > +++ b/include/linux/compaction.h
> > @@ -60,6 +60,15 @@ enum compact_result {
> >
> > struct alloc_context; /* in mm/internal.h */
> >
> > +// "node-%d"
> > +#define COMPACTION_STATE_NAME_LEN 16
> > +// Per-node compaction state
> > +struct compaction_state {
> > + int node_id;
> > + unsigned int proactiveness;
> > + char name[COMPACTION_STATE_NAME_LEN]; };
> > +
> > /*
> > * Number of free order-0 pages that should be available above given
> watermark
> > * to make sure compaction has reasonable chance of not running out
> > of free @@ -90,6 +99,7 @@ extern int sysctl_compaction_handler(struct
> > ctl_table *table, int write, extern int sysctl_extfrag_threshold;
> > extern int sysctl_compact_unevictable_allowed;
> >
> > +extern int extfrag_for_order(struct zone *zone, unsigned int order);
> > 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, diff --git
> > a/mm/compaction.c b/mm/compaction.c index 672d3c78c6ab..d906ccfedce0
> > 100644
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -25,6 +25,10 @@
> > #include <linux/psi.h>
> > #include "internal.h"
> >
> > +#ifdef CONFIG_COMPACTION
> > +static struct compaction_state compaction_states[MAX_NUMNODES];
> > +#endif
> > +
> > #ifdef CONFIG_COMPACTION
> > static inline void count_compact_event(enum vm_event_item item) { @@
> > -50,6 +54,8 @@ static inline void count_compact_events(enum
> vm_event_item item, long delta)
> > #define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
> > #define pageblock_end_pfn(pfn) block_end_pfn(pfn,
> pageblock_order)
> >
> > +static const int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
> > +
> > static unsigned long release_freepages(struct list_head *freelist) {
> > struct page *page, *next;
> > @@ -1846,6 +1852,51 @@ static inline bool is_via_compact_memory(int
> order)
> > return order == -1;
> > }
> >
> > +static int proactive_compaction_score_zone(struct zone *zone) {
> > + unsigned long score;
> > +
> > + score = zone->present_pages *
> > + extfrag_for_order(zone, HUGETLB_PAGE_ORDER);
> > + score = div64_ul(score,
> > + node_present_pages(zone->zone_pgdat->node_id) + 1);
> > + return score;
> > +}
> > +
> > +static int proactive_compaction_score_node(pg_data_t *pgdat) {
> > + unsigned long score = 0;
> > + int zoneid;
> > +
> > + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
> > + struct zone *zone;
> > +
> > + zone = &pgdat->node_zones[zoneid];
> > + score += proactive_compaction_score_zone(zone);
> > + }
> > +
> > + return score;
> > +}
> > +
> > +static int proactive_compaction_score_wmark(pg_data_t *pgdat, bool
> > +low) {
> > + int wmark_low;
> > +
> > + wmark_low = 100 - compaction_states[pgdat->node_id].proactiveness;
> > + return low ? wmark_low : min(wmark_low + 10, 100); }
> > +
> > +static bool should_proactive_compact_node(pg_data_t *pgdat) {
> > + int wmark_high;
> > +
> > + if (!compaction_states[pgdat->node_id].proactiveness)
> > + return false;
> > +
> > + wmark_high = proactive_compaction_score_wmark(pgdat, false);
> > + return proactive_compaction_score_node(pgdat) > wmark_high; }
> > +
> > static enum compact_result __compact_finished(struct compact_control
> > *cc) {
> > unsigned int order;
> > @@ -1872,6 +1923,19 @@ static enum compact_result
> __compact_finished(struct compact_control *cc)
> > return COMPACT_PARTIAL_SKIPPED;
> > }
> >
> > + if (cc->proactive_compaction) {
> > + int score, wmark_low;
> > +
> > + score = proactive_compaction_score_zone(cc->zone);
> > + wmark_low = proactive_compaction_score_wmark(
> > + cc->zone->zone_pgdat, true);
> > + if (score > wmark_low)
> > + ret = COMPACT_CONTINUE;
> > + else
> > + ret = COMPACT_SUCCESS;
> > + goto out;
> > + }
> > +
> > if (is_via_compact_memory(cc->order))
> > return COMPACT_CONTINUE;
> >
> > @@ -1930,6 +1994,7 @@ static enum compact_result
> __compact_finished(struct compact_control *cc)
> > }
> > }
> >
> > +out:
> > if (cc->contended || fatal_signal_pending(current))
> > ret = COMPACT_CONTENDED;
> >
> > @@ -2301,6 +2366,7 @@ static enum compact_result
> compact_zone_order(struct zone *zone, int order,
> > .alloc_flags = alloc_flags,
> > .classzone_idx = classzone_idx,
> > .direct_compaction = true,
> > + .proactive_compaction = false,
> > .whole_zone = (prio == MIN_COMPACT_PRIORITY),
> > .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
> > .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
> > @@ -2404,6 +2470,34 @@ enum compact_result
> try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> > return rc;
> > }
> >
> > +/* Compact all zones within a node according to proactiveness */
> > +static void proactive_compact_node(pg_data_t *pgdat) {
> > + int zoneid;
> > + struct zone *zone;
> > + struct compact_control cc = {
> > + .order = -1,
> > + .mode = MIGRATE_SYNC_LIGHT,
> > + .ignore_skip_hint = true,
> > + .whole_zone = true,
> > + .gfp_mask = GFP_KERNEL,
> > + .direct_compaction = false,
> > + .proactive_compaction = true,
> > + };
> > +
> > + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
> > + zone = &pgdat->node_zones[zoneid];
> > + if (!populated_zone(zone))
> > + continue;
> > +
> > + cc.zone = zone;
> > +
> > + compact_zone(&cc, NULL);
> > +
> > + VM_BUG_ON(!list_empty(&cc.freepages));
> > + VM_BUG_ON(!list_empty(&cc.migratepages));
> > + }
> > +}
> >
> > /* Compact all zones within a node */ static void compact_node(int
> > nid) @@ -2417,9 +2511,10 @@ static void compact_node(int nid)
> > .ignore_skip_hint = true,
> > .whole_zone = true,
> > .gfp_mask = GFP_KERNEL,
> > + .direct_compaction = false,
> > + .proactive_compaction = false,
> > };
> >
> > -
> > for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
> >
> > zone = &pgdat->node_zones[zoneid]; @@ -2492,6 +2587,118
> > @@ void compaction_unregister_node(struct node *node) } #endif /*
> > CONFIG_SYSFS && CONFIG_NUMA */
> >
> > +#ifdef CONFIG_SYSFS
> > +
> > +#define COMPACTION_ATTR_RO(_name) \
> > + static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> > +
> > +#define COMPACTION_ATTR(_name) \
> > + static struct kobj_attribute _name##_attr = \
> > + __ATTR(_name, 0644, _name##_show, _name##_store)
> > +
> > +static struct kobject *compaction_kobj; static struct kobject
> > +*compaction_kobjs[MAX_NUMNODES];
> > +
> > +static struct compaction_state *kobj_to_compaction_state(struct
> > +kobject *kobj) {
> > + int node;
> > +
> > + for_each_online_node(node) {
> > + if (compaction_kobjs[node] == kobj)
> > + return &compaction_states[node];
> > + }
> > +
> > + return NULL;
> > +}
> > +
> > +static ssize_t proactiveness_store(struct kobject *kobj,
> > + struct kobj_attribute *attr, const char *buf, size_t
> > +count) {
> > + int err;
> > + unsigned long input;
> > + struct compaction_state *c = kobj_to_compaction_state(kobj);
> > +
> > + err = kstrtoul(buf, 10, &input);
> > + if (err)
> > + return err;
> > + if (input > 100)
> > + return -EINVAL;
> > +
> > + c->proactiveness = input;
> > + return count;
> > +}
> > +
> > +static ssize_t proactiveness_show(struct kobject *kobj,
> > + struct kobj_attribute *attr, char *buf) {
> > + struct compaction_state *c = kobj_to_compaction_state(kobj);
> > +
> > + return sprintf(buf, "%u\n", c->proactiveness); }
> > +
> > +COMPACTION_ATTR(proactiveness);
> > +
> > +static struct attribute *compaction_attrs[] = {
> > + &proactiveness_attr.attr,
> > + NULL,
> > +};
> > +
> > +static const struct attribute_group compaction_attr_group = {
> > + .attrs = compaction_attrs,
> > +};
> > +
> > +static int compaction_sysfs_add_node(struct compaction_state *c,
> > + struct kobject *parent, struct kobject **compaction_kobjs,
> > + const struct attribute_group *compaction_attr_group) {
> > + int retval;
> > +
> > + compaction_kobjs[c->node_id] =
> > + kobject_create_and_add(c->name, parent);
> > + if (!compaction_kobjs[c->node_id])
> > + return -ENOMEM;
> > +
> > + retval = sysfs_create_group(compaction_kobjs[c->node_id],
> > + compaction_attr_group);
> > + if (retval)
> > + kobject_put(compaction_kobjs[c->node_id]);
> > +
> > + return retval;
> > +}
> > +
> > +static void __init compaction_sysfs_init(void) {
> > + struct compaction_state *c;
> > + int err, node;
> > +
> > + compaction_kobj = kobject_create_and_add("compaction", mm_kobj);
> > + if (!compaction_kobj)
> > + return;
> > +
> > + for_each_online_node(node) {
> > + c = &compaction_states[node];
> > + err = compaction_sysfs_add_node(c, compaction_kobj,
> > + compaction_kobjs,
> > + &compaction_attr_group);
> > + if (err)
> > + pr_err("compaction: Unable to add state %s", c->name);
> > + }
> > +}
> > +
> > +static void __init compaction_init(void) {
> > + int node;
> > +
> > + for_each_online_node(node) {
> > + struct compaction_state *c = &compaction_states[node];
> > +
> > + c->node_id = node;
> > + c->proactiveness = 0;
> > + snprintf(c->name, COMPACTION_STATE_NAME_LEN, "node-%d",
> node);
> > + }
> > +}
> > +#endif
> > +
> > static inline bool kcompactd_work_requested(pg_data_t *pgdat) {
> > return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
> > @@ -2532,6 +2739,8 @@ static void kcompactd_do_work(pg_data_t *pgdat)
> > .mode = MIGRATE_SYNC_LIGHT,
> > .ignore_skip_hint = false,
> > .gfp_mask = GFP_KERNEL,
> > + .direct_compaction = false,
> > + .proactive_compaction = false,
> > };
> > trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
> >
> > cc.classzone_idx); @@ -2629,6 +2838,7 @@ static int kcompactd(void *p)
> > {
> > pg_data_t *pgdat = (pg_data_t*)p;
> > struct task_struct *tsk = current;
> > + unsigned int proactive_defer = 0;
> >
> > const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> >
> > @@ -2644,12 +2854,29 @@ static int kcompactd(void *p)
> > unsigned long pflags;
> >
> > trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
> > - wait_event_freezable(pgdat->kcompactd_wait,
> > - kcompactd_work_requested(pgdat));
> > + if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
> > + kcompactd_work_requested(pgdat),
> > +
> > + msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
> >
> > - psi_memstall_enter(&pflags);
> > - kcompactd_do_work(pgdat);
> > - psi_memstall_leave(&pflags);
> > + psi_memstall_enter(&pflags);
> > + kcompactd_do_work(pgdat);
> > + psi_memstall_leave(&pflags);
> > + continue;
> > + }
> > +
> > + if (should_proactive_compact_node(pgdat)) {
> > + unsigned int prev_score, score;
> > +
> > + if (proactive_defer) {
> > + proactive_defer--;
> > + continue;
> > + }
> > + prev_score = proactive_compaction_score_node(pgdat);
> > + proactive_compact_node(pgdat);
> > + score = proactive_compaction_score_node(pgdat);
> > + proactive_defer = score < prev_score ?
> > + 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
> > + }
> > }
> >
> > return 0;
> > @@ -2726,6 +2953,9 @@ static int __init kcompactd_init(void)
> > return ret;
> > }
> >
> > + compaction_init();
> > + compaction_sysfs_init();
> > +
> > for_each_node_state(nid, N_MEMORY)
> > kcompactd_run(nid);
> > return 0;
> > diff --git a/mm/internal.h b/mm/internal.h index
> > 3cf20ab3ca01..e66bafd6c7a2 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -203,6 +203,7 @@ struct compact_control {
> > bool no_set_skip_hint; /* Don't mark blocks for skipping */
> > bool ignore_block_suitable; /* Scan blocks considered unsuitable */
> > bool direct_compaction; /* False from kcompactd or /proc/... */
> > + bool proactive_compaction; /* kcompactd proactive compaction */
> > bool whole_zone; /* Whole zone should/has been scanned */
> > bool contended; /* Signal lock or sched contention */
> > bool rescan; /* Rescanning the same pageblock */
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c index
> > 3c4eb750a199..e92c706e93ee 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8402,6 +8402,7 @@ int alloc_contig_range(unsigned long start,
> unsigned long end,
> > .ignore_skip_hint = true,
> > .no_set_skip_hint = true,
> > .gfp_mask = current_gfp_context(gfp_mask),
> > + .proactive_compaction = false,
> > };
> > INIT_LIST_HEAD(&cc.migratepages);
> >
> > diff --git a/mm/vmstat.c b/mm/vmstat.c index
> > 78d53378db99..70d724122643 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1074,6 +1074,18 @@ static int __fragmentation_index(unsigned int
> order, struct contig_page_info *in
> > return 1000 - div_u64( (1000+(div_u64(info->free_pages *
> > 1000ULL, requested))), info->free_blocks_total); }
> >
> > +int extfrag_for_order(struct zone *zone, unsigned int order) {
> > + struct contig_page_info info;
> > +
> > + fill_contig_page_info(zone, order, &info);
> > + if (info.free_pages == 0)
> > + return 0;
> > +
> > + return (info.free_pages - (info.free_blocks_suitable << order)) * 100
> > + /
> > +info.free_pages; }
> > +
> > /* Same as __fragmentation index but allocs contig_page_info on stack
> > */ int fragmentation_index(struct zone *zone, unsigned int order) {
> >
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