The patch titled
Subject: mm/page_alloc: replace local_lock with normal spinlock
has been added to the -mm mm-unstable branch. Its filename is
mm-page_alloc-replace-local_lock-with-normal-spinlock.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-replace-local_lock-with-normal-spinlock.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: replace local_lock with normal spinlock
Date: Fri, 24 Jun 2022 13:54:23 +0100
struct per_cpu_pages is no longer strictly local as PCP lists can be
drained remotely using a lock for protection. While the use of local_lock
works, it goes against the intent of local_lock which is for "pure CPU
local concurrency control mechanisms and not suited for inter-CPU
concurrency control" (Documentation/locking/locktypes.rst)
local_lock protects against migration between when the percpu pointer is
accessed and the pcp->lock acquired. The lock acquisition is a preemption
point so in the worst case, a task could migrate to another NUMA node and
accidentally allocate remote memory. The main requirement is to pin the
task to a CPU that is suitable for PREEMPT_RT and !PREEMPT_RT.
Replace local_lock with helpers that pin a task to a CPU, lookup the
per-cpu structure and acquire the embedded lock. It's similar to
local_lock without breaking the intent behind the API. It is not a
complete API as only the parts needed for PCP-alloc are implemented but in
theory, the generic helpers could be promoted to a general API if there
was demand for an embedded lock within a per-cpu struct with a guarantee
that the per-cpu structure locked matches the running CPU and cannot use
get_cpu_var due to RT concerns. PCP requires these semantics to avoid
accidentally allocating remote memory.
Link: https://lkml.kernel.org/r/20220624125423.6126-8-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 139 +++++++++++++++++++++++++++++++---------------
1 file changed, 95 insertions(+), 44 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-replace-local_lock-with-normal-spinlock
+++ a/mm/page_alloc.c
@@ -126,13 +126,6 @@ typedef int __bitwise fpi_t;
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
-struct pagesets {
- local_lock_t lock;
-};
-static DEFINE_PER_CPU(struct pagesets, pagesets) = {
- .lock = INIT_LOCAL_LOCK(lock),
-};
-
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
/*
* On SMP, spin_trylock is sufficient protection.
@@ -147,6 +140,83 @@ static DEFINE_PER_CPU(struct pagesets, p
#define pcp_trylock_finish(flags) local_irq_restore(flags)
#endif
+/*
+ * Locking a pcp requires a PCP lookup followed by a spinlock. To avoid
+ * a migration causing the wrong PCP to be locked and remote memory being
+ * potentially allocated, pin the task to the CPU for the lookup+lock.
+ * preempt_disable is used on !RT because it is faster than migrate_disable.
+ * migrate_disable is used on RT because otherwise RT spinlock usage is
+ * interfered with and a high priority task cannot preempt the allocator.
+ */
+#ifndef CONFIG_PREEMPT_RT
+#define pcpu_task_pin() preempt_disable()
+#define pcpu_task_unpin() preempt_enable()
+#else
+#define pcpu_task_pin() migrate_disable()
+#define pcpu_task_unpin() migrate_enable()
+#endif
+
+/*
+ * Generic helper to lookup and a per-cpu variable with an embedded spinlock.
+ * Return value should be used with equivalent unlock helper.
+ */
+#define pcpu_spin_lock(type, member, ptr) \
+({ \
+ type *_ret; \
+ pcpu_task_pin(); \
+ _ret = this_cpu_ptr(ptr); \
+ spin_lock(&_ret->member); \
+ _ret; \
+})
+
+#define pcpu_spin_lock_irqsave(type, member, ptr, flags) \
+({ \
+ type *_ret; \
+ pcpu_task_pin(); \
+ _ret = this_cpu_ptr(ptr); \
+ spin_lock_irqsave(&_ret->member, flags); \
+ _ret; \
+})
+
+#define pcpu_spin_trylock_irqsave(type, member, ptr, flags) \
+({ \
+ type *_ret; \
+ pcpu_task_pin(); \
+ _ret = this_cpu_ptr(ptr); \
+ if (!spin_trylock_irqsave(&_ret->member, flags)) { \
+ pcpu_task_unpin(); \
+ _ret = NULL; \
+ } \
+ _ret; \
+})
+
+#define pcpu_spin_unlock(member, ptr) \
+({ \
+ spin_unlock(&ptr->member); \
+ pcpu_task_unpin(); \
+})
+
+#define pcpu_spin_unlock_irqrestore(member, ptr, flags) \
+({ \
+ spin_unlock_irqrestore(&ptr->member, flags); \
+ pcpu_task_unpin(); \
+})
+
+/* struct per_cpu_pages specific helpers. */
+#define pcp_spin_lock(ptr) \
+ pcpu_spin_lock(struct per_cpu_pages, lock, ptr)
+
+#define pcp_spin_lock_irqsave(ptr, flags) \
+ pcpu_spin_lock_irqsave(struct per_cpu_pages, lock, ptr, flags)
+
+#define pcp_spin_trylock_irqsave(ptr, flags) \
+ pcpu_spin_trylock_irqsave(struct per_cpu_pages, lock, ptr, flags)
+
+#define pcp_spin_unlock(ptr) \
+ pcpu_spin_unlock(lock, ptr)
+
+#define pcp_spin_unlock_irqrestore(ptr, flags) \
+ pcpu_spin_unlock_irqrestore(lock, ptr, flags)
#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
DEFINE_PER_CPU(int, numa_node);
EXPORT_PER_CPU_SYMBOL(numa_node);
@@ -1485,10 +1555,7 @@ static void free_pcppages_bulk(struct zo
/* Ensure requested pindex is drained first. */
pindex = pindex - 1;
- /*
- * local_lock_irq held so equivalent to spin_lock_irqsave for
- * both PREEMPT_RT and non-PREEMPT_RT configurations.
- */
+ /* Caller must hold IRQ-safe pcp->lock so IRQs are disabled. */
spin_lock(&zone->lock);
isolated_pageblocks = has_isolate_pageblock(zone);
@@ -3056,10 +3123,7 @@ static int rmqueue_bulk(struct zone *zon
{
int i, allocated = 0;
- /*
- * local_lock_irq held so equivalent to spin_lock_irqsave for
- * both PREEMPT_RT and non-PREEMPT_RT configurations.
- */
+ /* Caller must hold IRQ-safe pcp->lock so IRQs are disabled. */
spin_lock(&zone->lock);
for (i = 0; i < count; ++i) {
struct page *page = __rmqueue(zone, order, migratetype,
@@ -3431,18 +3495,16 @@ void free_unref_page(struct page *page,
migratetype = MIGRATE_MOVABLE;
}
- local_lock_irqsave(&pagesets.lock, flags);
zone = page_zone(page);
pcp_trylock_prepare(UP_flags);
- pcp = this_cpu_ptr(zone->per_cpu_pageset);
- if (spin_trylock(&pcp->lock)) {
+ pcp = pcpu_spin_trylock_irqsave(struct per_cpu_pages, lock, zone->per_cpu_pageset, flags);
+ if (pcp) {
free_unref_page_commit(zone, pcp, page, migratetype, order);
- spin_unlock(&pcp->lock);
+ pcp_spin_unlock_irqrestore(pcp, flags);
} else {
free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
}
pcp_trylock_finish(UP_flags);
- local_unlock_irqrestore(&pagesets.lock, flags);
}
/*
@@ -3477,17 +3539,16 @@ void free_unref_page_list(struct list_he
}
}
- local_lock_irqsave(&pagesets.lock, flags);
list_for_each_entry_safe(page, next, list, lru) {
struct zone *zone = page_zone(page);
/* Different zone, different pcp lock. */
if (zone != locked_zone) {
if (pcp)
- spin_unlock(&pcp->lock);
+ pcp_spin_unlock_irqrestore(pcp, flags);
+
locked_zone = zone;
- pcp = this_cpu_ptr(zone->per_cpu_pageset);
- spin_lock(&pcp->lock);
+ pcp = pcp_spin_lock_irqsave(locked_zone->per_cpu_pageset, flags);
}
/*
@@ -3506,18 +3567,14 @@ void free_unref_page_list(struct list_he
* a large list of pages to free.
*/
if (++batch_count == SWAP_CLUSTER_MAX) {
- spin_unlock(&pcp->lock);
- local_unlock_irqrestore(&pagesets.lock, flags);
+ pcp_spin_unlock_irqrestore(pcp, flags);
batch_count = 0;
- local_lock_irqsave(&pagesets.lock, flags);
- pcp = this_cpu_ptr(locked_zone->per_cpu_pageset);
- spin_lock(&pcp->lock);
+ pcp = pcp_spin_lock_irqsave(locked_zone->per_cpu_pageset, flags);
}
}
if (pcp)
- spin_unlock(&pcp->lock);
- local_unlock_irqrestore(&pagesets.lock, flags);
+ pcp_spin_unlock_irqrestore(pcp, flags);
}
/*
@@ -3732,15 +3789,13 @@ static struct page *rmqueue_pcplist(stru
unsigned long flags;
unsigned long __maybe_unused UP_flags;
- local_lock_irqsave(&pagesets.lock, flags);
-
/*
* spin_trylock may fail due to a parallel drain. In the future, the
* trylock will also protect against IRQ reentrancy.
*/
- pcp = this_cpu_ptr(zone->per_cpu_pageset);
pcp_trylock_prepare(UP_flags);
- if (!spin_trylock(&pcp->lock)) {
+ pcp = pcp_spin_trylock_irqsave(zone->per_cpu_pageset, flags);
+ if (!pcp) {
pcp_trylock_finish(UP_flags);
return NULL;
}
@@ -3753,9 +3808,8 @@ static struct page *rmqueue_pcplist(stru
pcp->free_factor >>= 1;
list = &pcp->lists[order_to_pindex(migratetype, order)];
page = __rmqueue_pcplist(zone, order, migratetype, alloc_flags, pcp, list);
- spin_unlock(&pcp->lock);
+ pcp_spin_unlock_irqrestore(pcp, flags);
pcp_trylock_finish(UP_flags);
- local_unlock_irqrestore(&pagesets.lock, flags);
if (page) {
__count_zid_vm_events(PGALLOC, page_zonenum(page), 1);
zone_statistics(preferred_zone, zone, 1);
@@ -5349,10 +5403,9 @@ unsigned long __alloc_pages_bulk(gfp_t g
goto failed;
/* Is a parallel drain in progress? */
- local_lock_irqsave(&pagesets.lock, flags);
pcp_trylock_prepare(UP_flags);
- pcp = this_cpu_ptr(zone->per_cpu_pageset);
- if (!spin_trylock(&pcp->lock))
+ pcp = pcp_spin_trylock_irqsave(zone->per_cpu_pageset, flags);
+ if (!pcp)
goto failed_irq;
/* Attempt the batch allocation */
@@ -5370,7 +5423,7 @@ unsigned long __alloc_pages_bulk(gfp_t g
if (unlikely(!page)) {
/* Try and allocate at least one page */
if (!nr_account) {
- spin_unlock(&pcp->lock);
+ pcp_spin_unlock_irqrestore(pcp, flags);
goto failed_irq;
}
break;
@@ -5385,9 +5438,8 @@ unsigned long __alloc_pages_bulk(gfp_t g
nr_populated++;
}
- spin_unlock(&pcp->lock);
+ pcp_spin_unlock_irqrestore(pcp, flags);
pcp_trylock_finish(UP_flags);
- local_unlock_irqrestore(&pagesets.lock, flags);
__count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
@@ -5397,7 +5449,6 @@ out:
failed_irq:
pcp_trylock_finish(UP_flags);
- local_unlock_irqrestore(&pagesets.lock, flags);
failed:
page = __alloc_pages(gfp, 0, preferred_nid, nodemask);
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-page_alloc-add-page-buddy_list-and-page-pcp_list.patch
mm-page_alloc-use-only-one-pcp-list-for-thp-sized-allocations.patch
mm-page_alloc-split-out-buddy-removal-code-from-rmqueue-into-separate-helper.patch
mm-page_alloc-remove-mistaken-page-==-null-check-in-rmqueue.patch
mm-page_alloc-protect-pcp-lists-with-a-spinlock.patch
mm-page_alloc-replace-local_lock-with-normal-spinlock.patch
