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Date: Wed, 2 Jun 2021 11:14:56 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Michal Hocko <mhocko@...nel.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Vlastimil Babka <vbabka@...e.cz>,
Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: [PATCH v2 2/3] mm,memory_hotplug: Drop unneeded locking
Currently, memory-hotplug code takes zone's span_writelock
and pgdat's resize_lock when resizing the node/zone's spanned
pages via {move_pfn_range_to_zone(),remove_pfn_range_from_zone()}
and when resizing node and zone's present pages via
adjust_present_page_count().
These locks are also taken during the initialization of the system
at boot time, where it protects parallel struct page initialization,
but they should not really be needed in memory-hotplug where all
operations are a) synchronized on device level and b) serialized by
the mem_hotplug_lock lock.
Given that there are no users of span_seqlock, rip out all related
functions.
Signed-off-by: Oscar Salvador <osalvador@...e.de>
---
include/linux/memory_hotplug.h | 35 -----------------------------------
include/linux/mmzone.h | 23 +++++------------------
mm/memory_hotplug.c | 16 +---------------
mm/page_alloc.c | 1 -
4 files changed, 6 insertions(+), 69 deletions(-)
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 28f32fd00fe9..0d837ce6ec11 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -79,31 +79,7 @@ struct range mhp_get_pluggable_range(bool need_mapping);
/*
* Zone resizing functions
- *
- * Note: any attempt to resize a zone should has pgdat_resize_lock()
- * zone_span_writelock() both held. This ensure the size of a zone
- * can't be changed while pgdat_resize_lock() held.
*/
-static inline unsigned zone_span_seqbegin(struct zone *zone)
-{
- return read_seqbegin(&zone->span_seqlock);
-}
-static inline int zone_span_seqretry(struct zone *zone, unsigned iv)
-{
- return read_seqretry(&zone->span_seqlock, iv);
-}
-static inline void zone_span_writelock(struct zone *zone)
-{
- write_seqlock(&zone->span_seqlock);
-}
-static inline void zone_span_writeunlock(struct zone *zone)
-{
- write_sequnlock(&zone->span_seqlock);
-}
-static inline void zone_seqlock_init(struct zone *zone)
-{
- seqlock_init(&zone->span_seqlock);
-}
extern int zone_grow_free_lists(struct zone *zone, unsigned long new_nr_pages);
extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
@@ -248,17 +224,6 @@ void mem_hotplug_done(void);
___page; \
})
-static inline unsigned zone_span_seqbegin(struct zone *zone)
-{
- return 0;
-}
-static inline int zone_span_seqretry(struct zone *zone, unsigned iv)
-{
- return 0;
-}
-static inline void zone_span_writelock(struct zone *zone) {}
-static inline void zone_span_writeunlock(struct zone *zone) {}
-static inline void zone_seqlock_init(struct zone *zone) {}
static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
{
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0d53eba1c383..29cd230a383c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -13,7 +13,6 @@
#include <linux/threads.h>
#include <linux/numa.h>
#include <linux/init.h>
-#include <linux/seqlock.h>
#include <linux/nodemask.h>
#include <linux/pageblock-flags.h>
#include <linux/page-flags-layout.h>
@@ -528,18 +527,11 @@ struct zone {
*
* Locking rules:
*
- * zone_start_pfn and spanned_pages are protected by span_seqlock.
- * It is a seqlock because it has to be read outside of zone->lock,
- * and it is done in the main allocator path. But, it is written
- * quite infrequently.
- *
- * The span_seq lock is declared along with zone->lock because it is
- * frequently read in proximity to zone->lock. It's good to
- * give them a chance of being in the same cacheline.
- *
- * Write access to present_pages at runtime should be protected by
- * mem_hotplug_begin/end(). Any reader who can't tolerant drift of
- * present_pages should get_online_mems() to get a stable value.
+ * Besides system initialization functions, memory-hotplug is the only
+ * user that can change zone's {spanned,present} pages at runtime, and
+ * it does so by holding the mem_hotplug_lock lock. Any readers who
+ * can't tolerate drift values should use {get,put}_online_mems to get
+ * a stable value.
*/
atomic_long_t managed_pages;
unsigned long spanned_pages;
@@ -559,11 +551,6 @@ struct zone {
unsigned long nr_isolate_pageblock;
#endif
-#ifdef CONFIG_MEMORY_HOTPLUG
- /* see spanned/present_pages for more description */
- seqlock_t span_seqlock;
-#endif
-
int initialized;
/* Write-intensive fields used from the page allocator */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 70620d0dd923..62d5dc2c01de 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -445,7 +445,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
unsigned long pfn;
int nid = zone_to_nid(zone);
- zone_span_writelock(zone);
if (zone->zone_start_pfn == start_pfn) {
/*
* If the section is smallest section in the zone, it need
@@ -478,7 +477,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
zone->spanned_pages = 0;
}
}
- zone_span_writeunlock(zone);
}
static void update_pgdat_span(struct pglist_data *pgdat)
@@ -515,7 +513,7 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
{
const unsigned long end_pfn = start_pfn + nr_pages;
struct pglist_data *pgdat = zone->zone_pgdat;
- unsigned long pfn, cur_nr_pages, flags;
+ unsigned long pfn, cur_nr_pages;
/* Poison struct pages because they are now uninitialized again. */
for (pfn = start_pfn; pfn < end_pfn; pfn += cur_nr_pages) {
@@ -540,10 +538,8 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
clear_zone_contiguous(zone);
- pgdat_resize_lock(zone->zone_pgdat, &flags);
shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
update_pgdat_span(pgdat);
- pgdat_resize_unlock(zone->zone_pgdat, &flags);
set_zone_contiguous(zone);
}
@@ -750,19 +746,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
{
struct pglist_data *pgdat = zone->zone_pgdat;
int nid = pgdat->node_id;
- unsigned long flags;
clear_zone_contiguous(zone);
- /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
- pgdat_resize_lock(pgdat, &flags);
- zone_span_writelock(zone);
if (zone_is_empty(zone))
init_currently_empty_zone(zone, start_pfn, nr_pages);
resize_zone_range(zone, start_pfn, nr_pages);
- zone_span_writeunlock(zone);
resize_pgdat_range(pgdat, start_pfn, nr_pages);
- pgdat_resize_unlock(pgdat, &flags);
/*
* Subsection population requires care in pfn_to_online_page().
@@ -852,12 +842,8 @@ struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
*/
void adjust_present_page_count(struct zone *zone, long nr_pages)
{
- unsigned long flags;
-
zone->present_pages += nr_pages;
- pgdat_resize_lock(zone->zone_pgdat, &flags);
zone->zone_pgdat->node_present_pages += nr_pages;
- pgdat_resize_unlock(zone->zone_pgdat, &flags);
}
int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 296cb00802b4..27483245384c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7156,7 +7156,6 @@ static void __meminit zone_init_internals(struct zone *zone, enum zone_type idx,
zone->name = zone_names[idx];
zone->zone_pgdat = NODE_DATA(nid);
spin_lock_init(&zone->lock);
- zone_seqlock_init(zone);
zone_pcp_init(zone);
}
--
2.16.3
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