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 later.

It is possible for the local_lock to be embedded safely within struct
per_cpu_pages but it adds complexity to free_unref_page_list.

[akpm@linux-foundation.org: coding style fixes]
[mgorman@techsingularity.net: work around a pahole limitation with zero-sized struct pagesets]
Link: https://lkml.kernel.org/r/20210526080741.GW30378@techsingularity.net
[lkp@intel.com: Make pagesets static]

Link: https://lkml.kernel.org/r/20210512095458.30632-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index a50b123..0d6bb73 100644 (file)
--- 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/lib/Kconfig.debug b/lib/Kconfig.debug
index 7723f58..deca67d 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -313,6 +313,9 @@ config DEBUG_INFO_BTF
 config PAHOLE_HAS_SPLIT_BTF
        def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
 
+config PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT
+       def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "122")
+
 config DEBUG_INFO_BTF_MODULES
        def_bool y
        depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 330c730..89872ad 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -122,6 +122,24 @@ typedef int __bitwise fpi_t;
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_FRACTION   (8)
 
+struct pagesets {
+       local_lock_t lock;
+#if defined(CONFIG_DEBUG_INFO_BTF) &&                          \
+       !defined(CONFIG_DEBUG_LOCK_ALLOC) &&                    \
+       !defined(CONFIG_PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT)
+       /*
+        * pahole 1.21 and earlier gets confused by zero-sized per-CPU
+        * variables and produces invalid BTF. Ensure that
+        * sizeof(struct pagesets) != 0 for older versions of pahole.
+        */
+       char __pahole_hack;
+       #warning "pahole too old to support zero-sized struct pagesets"
+#endif
+};
+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);
@@ -1453,6 +1471,10 @@ static void free_pcppages_bulk(struct zone *zone, int count,
                } while (--count && --batch_free && !list_empty(list));
        }
 
+       /*
+        * local_lock_irq held so equivalent to spin_lock_irqsave for
+        * both PREEMPT_RT and non-PREEMPT_RT configurations.
+        */
        spin_lock(&zone->lock);
        isolated_pageblocks = has_isolate_pageblock(zone);
 
@@ -1573,6 +1595,11 @@ static void __free_pages_ok(struct page *page, unsigned int order,
                return;
 
        migratetype = get_pfnblock_migratetype(page, pfn);
+
+       /*
+        * TODO FIX: Disable IRQs before acquiring IRQ-safe zone->lock
+        * and protect vmstat updates.
+        */
        local_irq_save(flags);
        __count_vm_events(PGFREE, 1 << order);
        free_one_page(page_zone(page), page, pfn, order, migratetype,
@@ -2955,6 +2982,10 @@ 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.
+        */
        spin_lock(&zone->lock);
        for (i = 0; i < count; ++i) {
                struct page *page = __rmqueue(zone, order, migratetype,
@@ -3007,12 +3038,12 @@ 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
 
@@ -3028,13 +3059,13 @@ 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);
 }
 
 /*
@@ -3297,9 +3328,9 @@ 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);
 }
 
 /*
@@ -3319,7 +3350,7 @@ 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);
 
@@ -3332,12 +3363,12 @@ 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);
 }
 
 /*
@@ -3494,7 +3525,7 @@ 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);
@@ -3502,7 +3533,7 @@ 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;
 }
 
@@ -5103,7 +5134,7 @@ 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];
 
@@ -5141,12 +5172,12 @@ 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;
 
 failed_irq:
-       local_irq_restore(flags);
+       local_unlock_irqrestore(&pagesets.lock, flags);
 
 failed:
        page = __alloc_pages(gfp, 0, preferred_nid, nodemask);