[RFC PATCH 06/26] mm: page_alloc: consolidate free page accounting

Johannes Weiner
2023-04-18T19:14:25Z

Free page accounting currently happens a bit too high up the call
stack, where it has to deal with guard pages, compaction capturing,
block stealing and even page isolation. This is subtle and fragile,
and makes it difficult to hack on the code.

Push the accounting down to where pages enter and leave the physical
freelists, where all these higher-level exceptions are of no concern.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
include/linux/page-isolation.h | 2 +-
include/linux/vmstat.h | 8 --
mm/internal.h | 5 --
mm/page_alloc.c | 153 +++++++++++++++++----------------
mm/page_isolation.c | 13 ++-
5 files changed, 83 insertions(+), 98 deletions(-)

diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 0ab089e89db4..b519fffb3dee 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -35,7 +35,7 @@ static inline bool is_migrate_isolate(int migratetype)

void set_pageblock_migratetype(struct page *page, int migratetype);
int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable);
+ int old_mt, int new_mt, int *num_movable);

int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
int migratetype, int flags, gfp_t gfp_flags);
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 19cf5b6892ce..219ccf3f91cd 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -481,14 +481,6 @@ static inline void node_stat_sub_folio(struct folio *folio,
mod_node_page_state(folio_pgdat(folio), item, -folio_nr_pages(folio));
}

-static inline void __mod_zone_freepage_state(struct zone *zone, int nr_pages,
- int migratetype)
-{
- __mod_zone_page_state(zone, NR_FREE_PAGES, nr_pages);
- if (is_migrate_cma(migratetype))
- __mod_zone_page_state(zone, NR_FREE_CMA_PAGES, nr_pages);
-}
-
extern const char * const vmstat_text[];

static inline const char *zone_stat_name(enum zone_stat_item item)
diff --git a/mm/internal.h b/mm/internal.h
index bcf75a8b032d..024affd4e4b5 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -781,11 +781,6 @@ static inline bool is_migrate_highatomic(enum migratetype migratetype)
return migratetype == MIGRATE_HIGHATOMIC;
}

-static inline bool is_migrate_highatomic_page(struct page *page)
-{
- return get_pageblock_migratetype(page) == MIGRATE_HIGHATOMIC;
-}
-
void setup_zone_pageset(struct zone *zone);

struct migration_target_control {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d3d01019ce77..b9366c002334 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -843,7 +843,7 @@ static int __init debug_guardpage_minorder_setup(char *buf)
early_param("debug_guardpage_minorder", debug_guardpage_minorder_setup);

static inline bool set_page_guard(struct zone *zone, struct page *page,
- unsigned int order, int migratetype)
+ unsigned int order
{
if (!debug_guardpage_enabled())
return false;
@@ -854,15 +854,12 @@ static inline bool set_page_guard(struct zone *zone, struct page *page,
__SetPageGuard(page);
INIT_LIST_HEAD(&page->buddy_list);
set_page_private(page, order);
- /* Guard pages are not available for any usage */
- if (!is_migrate_isolate(migratetype))
- __mod_zone_freepage_state(zone, -(1 << order), migratetype);

return true;
}

static inline void clear_page_guard(struct zone *zone, struct page *page,
- unsigned int order, int migratetype)
+ unsigned int order)
{
if (!debug_guardpage_enabled())
return;
@@ -870,14 +867,12 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
__ClearPageGuard(page);

set_page_private(page, 0);
- if (!is_migrate_isolate(migratetype))
- __mod_zone_freepage_state(zone, (1 << order), migratetype);
}
#else
static inline bool set_page_guard(struct zone *zone, struct page *page,
- unsigned int order, int migratetype) { return false; }
+ unsigned int order) { return false; }
static inline void clear_page_guard(struct zone *zone, struct page *page,
- unsigned int order, int migratetype) {}
+ unsigned int order) {}
#endif

/*
@@ -994,24 +989,36 @@ compaction_capture(struct capture_control *capc, struct page *page,
}
#endif /* CONFIG_COMPACTION */

-/* Used for pages not on another list */
-static inline void add_to_free_list(struct page *page, struct zone *zone,
- unsigned int order, int migratetype)
+static inline void account_freepages(struct page *page, struct zone *zone,
+ int nr_pages, int migratetype)
{
- struct free_area *area = &zone->free_area[order];
+ if (is_migrate_isolate(migratetype))
+ return;

- list_add(&page->buddy_list, &area->free_list[migratetype]);
- area->nr_free++;
+ __mod_zone_page_state(zone, NR_FREE_PAGES, nr_pages);
+
+ if (is_migrate_cma(migratetype))
+ __mod_zone_page_state(zone, NR_FREE_CMA_PAGES, nr_pages);
}

/* Used for pages not on another list */
-static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
- unsigned int order, int migratetype)
+static inline void add_to_free_list(struct page *page, struct zone *zone,
+ unsigned int order, int migratetype,
+ bool tail)
{
struct free_area *area = &zone->free_area[order];

- list_add_tail(&page->buddy_list, &area->free_list[migratetype]);
+ VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
+ "page type is %lu, passed migratetype is %d (nr=%d)\n",
+ get_pageblock_migratetype(page), migratetype, 1 << order);
+
+ if (tail)
+ list_add_tail(&page->buddy_list, &area->free_list[migratetype]);
+ else
+ list_add(&page->buddy_list, &area->free_list[migratetype]);
area->nr_free++;
+
+ account_freepages(page, zone, 1 << order, migratetype);
}

/*
@@ -1020,16 +1027,23 @@ static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
* allocation again (e.g., optimization for memory onlining).
*/
static inline void move_to_free_list(struct page *page, struct zone *zone,
- unsigned int order, int migratetype)
+ unsigned int order, int old_mt, int new_mt)
{
struct free_area *area = &zone->free_area[order];

- list_move_tail(&page->buddy_list, &area->free_list[migratetype]);
+ list_move_tail(&page->buddy_list, &area->free_list[new_mt]);
+
+ account_freepages(page, zone, -(1 << order), old_mt);
+ account_freepages(page, zone, 1 << order, new_mt);
}

static inline void del_page_from_free_list(struct page *page, struct zone *zone,
- unsigned int order)
+ unsigned int order, int migratetype)
{
+ VM_WARN_ONCE(get_pageblock_migratetype(page) != migratetype,
+ "page type is %lu, passed migratetype is %d (nr=%d)\n",
+ get_pageblock_migratetype(page), migratetype, 1 << order);
+
/* clear reported state and update reported page count */
if (page_reported(page))
__ClearPageReported(page);
@@ -1038,6 +1052,8 @@ static inline void del_page_from_free_list(struct page *page, struct zone *zone,
__ClearPageBuddy(page);
set_page_private(page, 0);
zone->free_area[order].nr_free--;
+
+ account_freepages(page, zone, -(1 << order), migratetype);
}

/*
@@ -1104,23 +1120,21 @@ static inline void __free_one_page(struct page *page,
VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);

VM_BUG_ON(migratetype == -1);
- if (likely(!is_migrate_isolate(migratetype)))
- __mod_zone_freepage_state(zone, 1 << order, migratetype);
-
VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
VM_BUG_ON_PAGE(bad_range(zone, page), page);

while (order < MAX_ORDER - 1) {
- if (compaction_capture(capc, page, order, migratetype)) {
- __mod_zone_freepage_state(zone, -(1 << order),
- migratetype);
+ int buddy_mt;
+
+ if (compaction_capture(capc, page, order, migratetype))
return;
- }

buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
if (!buddy)
goto done_merging;

+ buddy_mt = get_pageblock_migratetype(buddy);
+
if (unlikely(order >= pageblock_order)) {
/*
* We want to prevent merge between freepages on pageblock
@@ -1128,8 +1142,6 @@ static inline void __free_one_page(struct page *page,
* pageblock isolation could cause incorrect freepage or CMA
* accounting or HIGHATOMIC accounting.
*/
- int buddy_mt = get_pageblock_migratetype(buddy);
-
if (migratetype != buddy_mt
&& (!migratetype_is_mergeable(migratetype) ||
!migratetype_is_mergeable(buddy_mt)))
@@ -1141,9 +1153,9 @@ static inline void __free_one_page(struct page *page,
* merge with it and move up one order.
*/
if (page_is_guard(buddy))
- clear_page_guard(zone, buddy, order, migratetype);
+ clear_page_guard(zone, buddy, order);
else
- del_page_from_free_list(buddy, zone, order);
+ del_page_from_free_list(buddy, zone, order, buddy_mt);
combined_pfn = buddy_pfn & pfn;
page = page + (combined_pfn - pfn);
pfn = combined_pfn;
@@ -1160,10 +1172,7 @@ static inline void __free_one_page(struct page *page,
else
to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);

- if (to_tail)
- add_to_free_list_tail(page, zone, order, migratetype);
- else
- add_to_free_list(page, zone, order, migratetype);
+ add_to_free_list(page, zone, order, migratetype, to_tail);

/* Notify page reporting subsystem of freed page */
if (!(fpi_flags & FPI_SKIP_REPORT_NOTIFY))
@@ -1205,10 +1214,8 @@ int split_free_page(struct page *free_page,
}

mt = get_pageblock_migratetype(free_page);
- if (likely(!is_migrate_isolate(mt)))
- __mod_zone_freepage_state(zone, -(1UL << order), mt);
+ del_page_from_free_list(free_page, zone, order, mt);

- del_page_from_free_list(free_page, zone, order);
for (pfn = free_page_pfn;
pfn < free_page_pfn + (1UL << order);) {
int mt = get_pfnblock_migratetype(pfn_to_page(pfn), pfn);
@@ -2352,10 +2359,10 @@ static inline void expand(struct zone *zone, struct page *page,
* Corresponding page table entries will not be touched,
* pages will stay not present in virtual address space
*/
- if (set_page_guard(zone, &page[size], high, migratetype))
+ if (set_page_guard(zone, &page[size], high))
continue;

- add_to_free_list(&page[size], zone, high, migratetype);
+ add_to_free_list(&page[size], zone, high, migratetype, false);
set_buddy_order(&page[size], high);
}
}
@@ -2559,11 +2566,15 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,

/* Find a page of the appropriate size in the preferred list */
for (current_order = order; current_order < MAX_ORDER; ++current_order) {
+ int actual_mt;
+
area = &(zone->free_area[current_order]);
page = get_page_from_free_area(area, migratetype);
if (!page)
continue;
- del_page_from_free_list(page, zone, current_order);
+ /* move_freepages_block() may strand types on wrong list */
+ actual_mt = get_pageblock_migratetype(page);
+ del_page_from_free_list(page, zone, current_order, actual_mt);
expand(zone, page, order, current_order, migratetype);
set_pcppage_migratetype(page, migratetype);
trace_mm_page_alloc_zone_locked(page, order, migratetype,
@@ -2606,7 +2617,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
*/
static int move_freepages(struct zone *zone,
unsigned long start_pfn, unsigned long end_pfn,
- int migratetype, int *num_movable)
+ int old_mt, int new_mt, int *num_movable)
{
struct page *page;
unsigned long pfn;
@@ -2633,7 +2644,7 @@ static int move_freepages(struct zone *zone,
VM_BUG_ON_PAGE(page_zone(page) != zone, page);

order = buddy_order(page);
- move_to_free_list(page, zone, order, migratetype);
+ move_to_free_list(page, zone, order, old_mt, new_mt);
pfn += 1 << order;
pages_moved += 1 << order;
}
@@ -2642,7 +2653,7 @@ static int move_freepages(struct zone *zone,
}

int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable)
+ int old_mt, int new_mt, int *num_movable)
{
unsigned long start_pfn, end_pfn, pfn;

@@ -2659,8 +2670,8 @@ int move_freepages_block(struct zone *zone, struct page *page,
if (!zone_spans_pfn(zone, end_pfn))
return 0;

- return move_freepages(zone, start_pfn, end_pfn, migratetype,
- num_movable);
+ return move_freepages(zone, start_pfn, end_pfn,
+ old_mt, new_mt, num_movable);
}

static void change_pageblock_range(struct page *pageblock_page,
@@ -2786,8 +2797,9 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
if (!whole_block)
goto single_page;

- free_pages = move_freepages_block(zone, page, start_type,
- &movable_pages);
+ free_pages = move_freepages_block(zone, page, old_block_type,
+ start_type, &movable_pages);
+
/*
* Determine how many pages are compatible with our allocation.
* For movable allocation, it's the number of movable pages which
@@ -2825,7 +2837,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
return;

single_page:
- move_to_free_list(page, zone, current_order, start_type);
+ move_to_free_list(page, zone, current_order,
+ old_block_type, start_type);
}

/*
@@ -2895,7 +2908,7 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
if (migratetype_is_mergeable(mt)) {
zone->nr_reserved_highatomic += pageblock_nr_pages;
set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
- move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
+ move_freepages_block(zone, page, mt, MIGRATE_HIGHATOMIC, NULL);
}

out_unlock:
@@ -2935,11 +2948,13 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
spin_lock_irqsave(&zone->lock, flags);
for (order = 0; order < MAX_ORDER; order++) {
struct free_area *area = &(zone->free_area[order]);
+ int mt;

page = get_page_from_free_area(area, MIGRATE_HIGHATOMIC);
if (!page)
continue;

+ mt = get_pageblock_migratetype(page);
/*
* In page freeing path, migratetype change is racy so
* we can counter several free pages in a pageblock
@@ -2947,7 +2962,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
* from highatomic to ac->migratetype. So we should
* adjust the count once.
*/
- if (is_migrate_highatomic_page(page)) {
+ if (is_migrate_highatomic(mt)) {
/*
* It should never happen but changes to
* locking could inadvertently allow a per-cpu
@@ -2970,8 +2985,8 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
* may increase.
*/
set_pageblock_migratetype(page, ac->migratetype);
- ret = move_freepages_block(zone, page, ac->migratetype,
- NULL);
+ ret = move_freepages_block(zone, page, mt,
+ ac->migratetype, NULL);
if (ret) {
spin_unlock_irqrestore(&zone->lock, flags);
return ret;
@@ -3142,18 +3157,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
list_add_tail(&page->pcp_list, list);
allocated++;
- if (is_migrate_cma(get_pcppage_migratetype(page)))
- __mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
- -(1 << order));
}
-
- /*
- * i pages were removed from the buddy list even if some leak due
- * to check_pcp_refill failing so adjust NR_FREE_PAGES based
- * on i. Do not confuse with 'allocated' which is the number of
- * pages added to the pcp list.
- */
- __mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
spin_unlock_irqrestore(&zone->lock, flags);
return allocated;
}
@@ -3615,11 +3619,9 @@ int __isolate_free_page(struct page *page, unsigned int order)
watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
return 0;
-
- __mod_zone_freepage_state(zone, -(1UL << order), mt);
}

- del_page_from_free_list(page, zone, order);
+ del_page_from_free_list(page, zone, order, mt);

/*
* Set the pageblock if the isolated page is at least half of a
@@ -3715,8 +3717,6 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone,
return NULL;
}
}
- __mod_zone_freepage_state(zone, -(1 << order),
- get_pcppage_migratetype(page));
spin_unlock_irqrestore(&zone->lock, flags);
} while (check_new_pages(page, order));

@@ -9578,8 +9578,9 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)

BUG_ON(page_count(page));
BUG_ON(!PageBuddy(page));
+ VM_WARN_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE);
order = buddy_order(page);
- del_page_from_free_list(page, zone, order);
+ del_page_from_free_list(page, zone, order, MIGRATE_ISOLATE);
pfn += (1 << order);
}
spin_unlock_irqrestore(&zone->lock, flags);
@@ -9630,11 +9631,12 @@ static void break_down_buddy_pages(struct zone *zone, struct page *page,
current_buddy = page + size;
}

- if (set_page_guard(zone, current_buddy, high, migratetype))
+ if (set_page_guard(zone, current_buddy, high))
continue;

if (current_buddy != target) {
- add_to_free_list(current_buddy, zone, high, migratetype);
+ add_to_free_list(current_buddy, zone, high,
+ migratetype, false);
set_buddy_order(current_buddy, high);
page = next_page;
}
@@ -9662,12 +9664,11 @@ bool take_page_off_buddy(struct page *page)
int migratetype = get_pfnblock_migratetype(page_head,
pfn_head);

- del_page_from_free_list(page_head, zone, page_order);
+ del_page_from_free_list(page_head, zone, page_order,
+ migratetype);
break_down_buddy_pages(zone, page_head, page, 0,
page_order, migratetype);
SetPageHWPoisonTakenOff(page);
- if (!is_migrate_isolate(migratetype))
- __mod_zone_freepage_state(zone, -1, migratetype);
ret = true;
break;
}
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index b67800f7f6b1..e119a37ac661 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -183,10 +183,8 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_

set_pageblock_migratetype(page, MIGRATE_ISOLATE);
zone->nr_isolate_pageblock++;
- nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
- NULL);
-
- __mod_zone_freepage_state(zone, -nr_pages, mt);
+ nr_pages = move_freepages_block(zone, page, mt,
+ MIGRATE_ISOLATE, NULL);
spin_unlock_irqrestore(&zone->lock, flags);
return 0;
}
@@ -251,10 +249,9 @@ static void unset_migratetype_isolate(struct page *page, int migratetype)
* onlining - just onlined memory won't immediately be considered for
* allocation.
*/
- if (!isolated_page) {
- nr_pages = move_freepages_block(zone, page, migratetype, NULL);
- __mod_zone_freepage_state(zone, nr_pages, migratetype);
- }
+ if (!isolated_page)
+ nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
+ migratetype, NULL);
set_pageblock_migratetype(page, migratetype);
if (isolated_page)
__putback_isolated_page(page, order, migratetype);
--
2.39.2