Commit 01b44456 authored by Mel Gorman's avatar Mel Gorman Committed by Andrew Morton
Browse files

mm/page_alloc: replace local_lock with normal spinlock 

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.

[mgorman@techsingularity.net: use pcp_spin_trylock_irqsave instead of pcpu_spin_trylock_irqsave]
  Link: https://lkml.kernel.org/r/20220627084645.GA27531@techsingularity.net
Link: https://lkml.kernel.org/r/20220624125423.6126-8-mgorman@techsingularity.net


Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Tested-by: default avatarYu Zhao <yuzhao@google.com>
Reviewed-by: default avatarNicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: default avatarNicolas Saenz Julienne <nsaenzju@redhat.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Tested-by: default avatarYu Zhao <yuzhao@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 443c2acc

mm/page_alloc.c

+95 −45
Original line number Diff line number Diff line
@@ -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, pagesets) = { 
#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 zone *zone, int count, 
	/* 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 *zone, unsigned int order, 
{

	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, unsigned int order) 
		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 = pcp_spin_trylock_irqsave(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_head *list) 
		}

	}



	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_head *list) 
		 * 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);

}



/*
@@ -3732,17 +3789,14 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, 
	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);

		local_unlock_irqrestore(&pagesets.lock, flags);

		return NULL;

	}
@@ -3754,9 +3808,8 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, 
	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);
@@ -5358,10 +5411,9 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, 
		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 */
@@ -5379,7 +5431,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, 
		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;
@@ -5394,9 +5446,8 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, 
		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);
@@ -5406,7 +5457,6 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, 


failed_irq:

	pcp_trylock_finish(UP_flags);

	local_unlock_irqrestore(&pagesets.lock, flags);



failed:

	page = __alloc_pages(gfp, 0, preferred_nid, nodemask);