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Subject[PATCH v5 2/4] mm: convert zone->managed_pages to atomic variable
Date
totalram_pages, zone->managed_pages and totalhigh_pages updates
are protected by managed_page_count_lock, but readers never care
about it. Convert these variables to atomic to avoid readers
potentially seeing a store tear.

This patch converts zone->managed_pages. Subsequent patches will
convert totalram_panges, totalhigh_pages and eventually
managed_page_count_lock will be removed.

Main motivation was that managed_page_count_lock handling was
complicating things. It was discussed in length here,
https://lore.kernel.org/patchwork/patch/995739/#1181785
So it seemes better to remove the lock and convert variables
to atomic, with preventing poteintial store-to-read tearing as
a bonus.

Suggested-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Arun KS <arunks@codeaurora.org>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
Most of the changes are done by below coccinelle script,

@@
struct zone *z;
expression e1;
@@
(
- z->managed_pages = e1
+ atomic_long_set(&z->managed_pages, e1)
|
- e1->managed_pages++
+ atomic_long_inc(&e1->managed_pages)
|
- z->managed_pages
+ zone_managed_pages(z)
)

@@
expression e,e1;
@@
- e->managed_pages += e1
+ atomic_long_add(e1, &e->managed_pages)

@@
expression z;
@@
- z.managed_pages
+ zone_managed_pages(&z)

Then, manually apply following change,
include/linux/mmzone.h

- unsigned long managed_pages;
+ atomic_long_t managed_pages;

+static inline unsigned long zone_managed_pages(struct zone *zone)
+{
+ return (unsigned long)atomic_long_read(&zone->managed_pages);
+}

---

drivers/gpu/drm/amd/amdkfd/kfd_crat.c | 2 +-
include/linux/mmzone.h | 9 +++++--
lib/show_mem.c | 2 +-
mm/memblock.c | 2 +-
mm/page_alloc.c | 44 +++++++++++++++++------------------
mm/vmstat.c | 4 ++--
6 files changed, 34 insertions(+), 29 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_crat.c b/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
index 56412b0..c0e55bb 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
@@ -848,7 +848,7 @@ static int kfd_fill_mem_info_for_cpu(int numa_node_id, int *avail_size,
*/
pgdat = NODE_DATA(numa_node_id);
for (zone_type = 0; zone_type < MAX_NR_ZONES; zone_type++)
- mem_in_bytes += pgdat->node_zones[zone_type].managed_pages;
+ mem_in_bytes += zone_managed_pages(&pgdat->node_zones[zone_type]);
mem_in_bytes <<= PAGE_SHIFT;

sub_type_hdr->length_low = lower_32_bits(mem_in_bytes);
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 847705a..e73dc31 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -435,7 +435,7 @@ struct zone {
* adjust_managed_page_count() should be used instead of directly
* touching zone->managed_pages and totalram_pages.
*/
- unsigned long managed_pages;
+ atomic_long_t managed_pages;
unsigned long spanned_pages;
unsigned long present_pages;

@@ -524,6 +524,11 @@ enum pgdat_flags {
PGDAT_RECLAIM_LOCKED, /* prevents concurrent reclaim */
};

+static inline unsigned long zone_managed_pages(struct zone *zone)
+{
+ return (unsigned long)atomic_long_read(&zone->managed_pages);
+}
+
static inline unsigned long zone_end_pfn(const struct zone *zone)
{
return zone->zone_start_pfn + zone->spanned_pages;
@@ -814,7 +819,7 @@ static inline bool is_dev_zone(const struct zone *zone)
*/
static inline bool managed_zone(struct zone *zone)
{
- return zone->managed_pages;
+ return zone_managed_pages(zone);
}

/* Returns true if a zone has memory */
diff --git a/lib/show_mem.c b/lib/show_mem.c
index 0beaa1d..eefe67d 100644
--- a/lib/show_mem.c
+++ b/lib/show_mem.c
@@ -28,7 +28,7 @@ void show_mem(unsigned int filter, nodemask_t *nodemask)
continue;

total += zone->present_pages;
- reserved += zone->present_pages - zone->managed_pages;
+ reserved += zone->present_pages - zone_managed_pages(zone);

if (is_highmem_idx(zoneid))
highmem += zone->present_pages;
diff --git a/mm/memblock.c b/mm/memblock.c
index 7df468c..bbd82ab 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1950,7 +1950,7 @@ void reset_node_managed_pages(pg_data_t *pgdat)
struct zone *z;

for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
- z->managed_pages = 0;
+ atomic_long_set(&z->managed_pages, 0);
}

void __init reset_all_zones_managed_pages(void)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 173312b..22e6645 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1279,7 +1279,7 @@ static void __init __free_pages_boot_core(struct page *page, unsigned int order)
__ClearPageReserved(p);
set_page_count(p, 0);

- page_zone(page)->managed_pages += nr_pages;
+ atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
set_page_refcounted(page);
__free_pages(page, order);
}
@@ -2258,7 +2258,7 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
* Limit the number reserved to 1 pageblock or roughly 1% of a zone.
* Check is race-prone but harmless.
*/
- max_managed = (zone->managed_pages / 100) + pageblock_nr_pages;
+ max_managed = (zone_managed_pages(zone) / 100) + pageblock_nr_pages;
if (zone->nr_reserved_highatomic >= max_managed)
return;

@@ -4662,7 +4662,7 @@ static unsigned long nr_free_zone_pages(int offset)
struct zonelist *zonelist = node_zonelist(numa_node_id(), GFP_KERNEL);

for_each_zone_zonelist(zone, z, zonelist, offset) {
- unsigned long size = zone->managed_pages;
+ unsigned long size = zone_managed_pages(zone);
unsigned long high = high_wmark_pages(zone);
if (size > high)
sum += size - high;
@@ -4769,7 +4769,7 @@ void si_meminfo_node(struct sysinfo *val, int nid)
pg_data_t *pgdat = NODE_DATA(nid);

for (zone_type = 0; zone_type < MAX_NR_ZONES; zone_type++)
- managed_pages += pgdat->node_zones[zone_type].managed_pages;
+ managed_pages += zone_managed_pages(&pgdat->node_zones[zone_type]);
val->totalram = managed_pages;
val->sharedram = node_page_state(pgdat, NR_SHMEM);
val->freeram = sum_zone_node_page_state(nid, NR_FREE_PAGES);
@@ -4778,7 +4778,7 @@ void si_meminfo_node(struct sysinfo *val, int nid)
struct zone *zone = &pgdat->node_zones[zone_type];

if (is_highmem(zone)) {
- managed_highpages += zone->managed_pages;
+ managed_highpages += zone_managed_pages(zone);
free_highpages += zone_page_state(zone, NR_FREE_PAGES);
}
}
@@ -4985,7 +4985,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
K(zone_page_state(zone, NR_ZONE_UNEVICTABLE)),
K(zone_page_state(zone, NR_ZONE_WRITE_PENDING)),
K(zone->present_pages),
- K(zone->managed_pages),
+ K(zone_managed_pages(zone)),
K(zone_page_state(zone, NR_MLOCK)),
zone_page_state(zone, NR_KERNEL_STACK_KB),
K(zone_page_state(zone, NR_PAGETABLE)),
@@ -5645,7 +5645,7 @@ static int zone_batchsize(struct zone *zone)
* The per-cpu-pages pools are set to around 1000th of the
* size of the zone.
*/
- batch = zone->managed_pages / 1024;
+ batch = zone_managed_pages(zone) / 1024;
/* But no more than a meg. */
if (batch * PAGE_SIZE > 1024 * 1024)
batch = (1024 * 1024) / PAGE_SIZE;
@@ -5756,7 +5756,7 @@ static void pageset_set_high_and_batch(struct zone *zone,
{
if (percpu_pagelist_fraction)
pageset_set_high(pcp,
- (zone->managed_pages /
+ (zone_managed_pages(zone) /
percpu_pagelist_fraction));
else
pageset_set_batch(pcp, zone_batchsize(zone));
@@ -6311,7 +6311,7 @@ static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
static void __meminit zone_init_internals(struct zone *zone, enum zone_type idx, int nid,
unsigned long remaining_pages)
{
- zone->managed_pages = remaining_pages;
+ atomic_long_set(&zone->managed_pages, remaining_pages);
zone_set_nid(zone, nid);
zone->name = zone_names[idx];
zone->zone_pgdat = NODE_DATA(nid);
@@ -7064,7 +7064,7 @@ static int __init cmdline_parse_movablecore(char *p)
void adjust_managed_page_count(struct page *page, long count)
{
spin_lock(&managed_page_count_lock);
- page_zone(page)->managed_pages += count;
+ atomic_long_add(count, &page_zone(page)->managed_pages);
totalram_pages += count;
#ifdef CONFIG_HIGHMEM
if (PageHighMem(page))
@@ -7112,7 +7112,7 @@ void free_highmem_page(struct page *page)
{
__free_reserved_page(page);
totalram_pages++;
- page_zone(page)->managed_pages++;
+ atomic_long_inc(&page_zone(page)->managed_pages);
totalhigh_pages++;
}
#endif
@@ -7245,7 +7245,7 @@ static void calculate_totalreserve_pages(void)
for (i = 0; i < MAX_NR_ZONES; i++) {
struct zone *zone = pgdat->node_zones + i;
long max = 0;
- unsigned long managed_pages = zone->managed_pages;
+ unsigned long managed_pages = zone_managed_pages(zone);

/* Find valid and maximum lowmem_reserve in the zone */
for (j = i; j < MAX_NR_ZONES; j++) {
@@ -7281,7 +7281,7 @@ static void setup_per_zone_lowmem_reserve(void)
for_each_online_pgdat(pgdat) {
for (j = 0; j < MAX_NR_ZONES; j++) {
struct zone *zone = pgdat->node_zones + j;
- unsigned long managed_pages = zone->managed_pages;
+ unsigned long managed_pages = zone_managed_pages(zone);

zone->lowmem_reserve[j] = 0;

@@ -7299,7 +7299,7 @@ static void setup_per_zone_lowmem_reserve(void)
lower_zone->lowmem_reserve[j] =
managed_pages / sysctl_lowmem_reserve_ratio[idx];
}
- managed_pages += lower_zone->managed_pages;
+ managed_pages += zone_managed_pages(lower_zone);
}
}
}
@@ -7318,14 +7318,14 @@ static void __setup_per_zone_wmarks(void)
/* Calculate total number of !ZONE_HIGHMEM pages */
for_each_zone(zone) {
if (!is_highmem(zone))
- lowmem_pages += zone->managed_pages;
+ lowmem_pages += zone_managed_pages(zone);
}

for_each_zone(zone) {
u64 tmp;

spin_lock_irqsave(&zone->lock, flags);
- tmp = (u64)pages_min * zone->managed_pages;
+ tmp = (u64)pages_min * zone_managed_pages(zone);
do_div(tmp, lowmem_pages);
if (is_highmem(zone)) {
/*
@@ -7339,7 +7339,7 @@ static void __setup_per_zone_wmarks(void)
*/
unsigned long min_pages;

- min_pages = zone->managed_pages / 1024;
+ min_pages = zone_managed_pages(zone) / 1024;
min_pages = clamp(min_pages, SWAP_CLUSTER_MAX, 128UL);
zone->watermark[WMARK_MIN] = min_pages;
} else {
@@ -7356,7 +7356,7 @@ static void __setup_per_zone_wmarks(void)
* ensure a minimum size on small systems.
*/
tmp = max_t(u64, tmp >> 2,
- mult_frac(zone->managed_pages,
+ mult_frac(zone_managed_pages(zone),
watermark_scale_factor, 10000));

zone->watermark[WMARK_LOW] = min_wmark_pages(zone) + tmp;
@@ -7486,8 +7486,8 @@ static void setup_min_unmapped_ratio(void)
pgdat->min_unmapped_pages = 0;

for_each_zone(zone)
- zone->zone_pgdat->min_unmapped_pages += (zone->managed_pages *
- sysctl_min_unmapped_ratio) / 100;
+ zone->zone_pgdat->min_unmapped_pages += (zone_managed_pages(zone) *
+ sysctl_min_unmapped_ratio) / 100;
}


@@ -7514,8 +7514,8 @@ static void setup_min_slab_ratio(void)
pgdat->min_slab_pages = 0;

for_each_zone(zone)
- zone->zone_pgdat->min_slab_pages += (zone->managed_pages *
- sysctl_min_slab_ratio) / 100;
+ zone->zone_pgdat->min_slab_pages += (zone_managed_pages(zone) *
+ sysctl_min_slab_ratio) / 100;
}

int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *table, int write,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 6038ce5..9fee037 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -227,7 +227,7 @@ int calculate_normal_threshold(struct zone *zone)
* 125 1024 10 16-32 GB 9
*/

- mem = zone->managed_pages >> (27 - PAGE_SHIFT);
+ mem = zone_managed_pages(zone) >> (27 - PAGE_SHIFT);

threshold = 2 * fls(num_online_cpus()) * (1 + fls(mem));

@@ -1569,7 +1569,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
high_wmark_pages(zone),
zone->spanned_pages,
zone->present_pages,
- zone->managed_pages);
+ zone_managed_pages(zone));

seq_printf(m,
"\n protection: (%ld",
--
1.9.1
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