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Date: Mon, 29 Mar 2021 13:06:44 +0100
From: Mel Gorman <mgorman@...hsingularity.net>
To: Linux-MM <linux-mm@...ck.org>
Cc: Linux-RT-Users <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Chuck Lever <chuck.lever@...cle.com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 2/6] mm/page_alloc: Convert per-cpu list protection to local_lock
There is a lack of clarity of what exactly local_irq_save/local_irq_restore
protects in page_alloc.c . It conflates the protection of per-cpu page
allocation structures with per-cpu vmstat deltas.
This patch protects the PCP structure using local_lock which
for most configurations is identical to IRQ enabling/disabling.
The scope of the lock is still wider than it should be but this is
decreased in later patches. The per-cpu vmstat deltas are protected by
preempt_disable/preempt_enable where necessary instead of relying on
IRQ disable/enable.
[lkp@...el.com: Make pagesets static]
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
include/linux/mmzone.h | 2 ++
mm/page_alloc.c | 43 ++++++++++++++++++++++++------------------
mm/vmstat.c | 4 ++++
3 files changed, 31 insertions(+), 18 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index a4393ac27336..106da8fbc72a 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -20,6 +20,7 @@
#include <linux/atomic.h>
#include <linux/mm_types.h>
#include <linux/page-flags.h>
+#include <linux/local_lock.h>
#include <asm/page.h>
/* Free memory management - zoned buddy allocator. */
@@ -337,6 +338,7 @@ enum zone_watermarks {
#define high_wmark_pages(z) (z->_watermark[WMARK_HIGH] + z->watermark_boost)
#define wmark_pages(z, i) (z->_watermark[i] + z->watermark_boost)
+/* Fields and list protected by pagesets local_lock in page_alloc.c */
struct per_cpu_pages {
int count; /* number of pages in the list */
int high; /* high watermark, emptying needed */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 32006e66564a..7f8c73020688 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -112,6 +112,13 @@ typedef int __bitwise fpi_t;
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_FRACTION (8)
+struct pagesets {
+ local_lock_t lock;
+};
+static DEFINE_PER_CPU(struct pagesets, pagesets) = {
+ .lock = INIT_LOCAL_LOCK(lock),
+};
+
#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
DEFINE_PER_CPU(int, numa_node);
EXPORT_PER_CPU_SYMBOL(numa_node);
@@ -2962,12 +2969,12 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
unsigned long flags;
int to_drain, batch;
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
batch = READ_ONCE(pcp->batch);
to_drain = min(pcp->count, batch);
if (to_drain > 0)
free_pcppages_bulk(zone, to_drain, pcp);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
}
#endif
@@ -2983,13 +2990,13 @@ static void drain_pages_zone(unsigned int cpu, struct zone *zone)
unsigned long flags;
struct per_cpu_pages *pcp;
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
if (pcp->count)
free_pcppages_bulk(zone, pcp->count, pcp);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
}
/*
@@ -3252,9 +3259,9 @@ void free_unref_page(struct page *page)
if (!free_unref_page_prepare(page, pfn))
return;
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
free_unref_page_commit(page, pfn);
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
}
/*
@@ -3274,7 +3281,7 @@ void free_unref_page_list(struct list_head *list)
set_page_private(page, pfn);
}
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
list_for_each_entry_safe(page, next, list, lru) {
unsigned long pfn = page_private(page);
@@ -3287,12 +3294,12 @@ void free_unref_page_list(struct list_head *list)
* a large list of pages to free.
*/
if (++batch_count == SWAP_CLUSTER_MAX) {
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
batch_count = 0;
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
}
}
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
}
/*
@@ -3449,7 +3456,7 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
struct page *page;
unsigned long flags;
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
pcp = this_cpu_ptr(zone->per_cpu_pageset);
list = &pcp->lists[migratetype];
page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list);
@@ -3457,7 +3464,7 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
__count_zid_vm_events(PGALLOC, page_zonenum(page), 1);
zone_statistics(preferred_zone, zone);
}
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
return page;
}
@@ -5052,7 +5059,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
goto failed;
/* Attempt the batch allocation */
- local_irq_save(flags);
+ local_lock_irqsave(&pagesets.lock, flags);
pcp = this_cpu_ptr(zone->per_cpu_pageset);
pcp_list = &pcp->lists[ac.migratetype];
@@ -5090,7 +5097,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
nr_populated++;
}
- local_irq_restore(flags);
+ local_unlock_irqrestore(&pagesets.lock, flags);
return nr_populated;
@@ -8958,12 +8965,13 @@ void zone_pcp_enable(struct zone *zone)
void zone_pcp_reset(struct zone *zone)
{
- unsigned long flags;
int cpu;
struct per_cpu_zonestat *pzstats;
- /* avoid races with drain_pages() */
- local_irq_save(flags);
+ /*
+ * No race with drain_pages. drain_zonestat disables preemption
+ * and drain_pages relies on the pcp local_lock.
+ */
if (zone->per_cpu_pageset != &boot_pageset) {
for_each_online_cpu(cpu) {
pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
@@ -8974,7 +8982,6 @@ void zone_pcp_reset(struct zone *zone)
zone->per_cpu_pageset = &boot_pageset;
zone->per_cpu_zonestats = &boot_zonestats;
}
- local_irq_restore(flags);
}
#ifdef CONFIG_MEMORY_HOTREMOVE
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8a8f1a26b231..01b74ff73549 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -887,6 +887,7 @@ void cpu_vm_stats_fold(int cpu)
pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
+ preempt_disable();
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
if (pzstats->vm_stat_diff[i]) {
int v;
@@ -908,6 +909,7 @@ void cpu_vm_stats_fold(int cpu)
global_numa_diff[i] += v;
}
#endif
+ preempt_enable();
}
for_each_online_pgdat(pgdat) {
@@ -941,6 +943,7 @@ void drain_zonestat(struct zone *zone, struct per_cpu_zonestat *pzstats)
{
int i;
+ preempt_disable();
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
if (pzstats->vm_stat_diff[i]) {
int v = pzstats->vm_stat_diff[i];
@@ -959,6 +962,7 @@ void drain_zonestat(struct zone *zone, struct per_cpu_zonestat *pzstats)
atomic_long_add(v, &vm_numa_stat[i]);
}
#endif
+ preempt_enable();
}
#endif
--
2.26.2
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