+ mm-page_alloc-add-page-buddy_list-and-page-pcp_list.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/page_alloc: add page->buddy_list and page->pcp_list
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-add-page-buddy_list-and-page-pcp_list.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-add-page-buddy_list-and-page-pcp_list.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Mel Gorman <mgorman@techsingularity.net>
Subject: mm/page_alloc: add page->buddy_list and page->pcp_list

Patch series "Drain remote per-cpu directly", v3.

This series has the same intent as Nicolas' series "mm/page_alloc: Remote
per-cpu lists drain support" -- avoid interference of a high priority task
due to a workqueue item draining per-cpu page lists.  While many workloads
can tolerate a brief interruption, it may cause a real-time task running
on a NOHZ_FULL CPU to miss a deadline and at minimum, the draining is
non-deterministic.

Currently an IRQ-safe local_lock protects the page allocator per-cpu
lists.  The local_lock on its own prevents migration and the IRQ disabling
protects from corruption due to an interrupt arriving while a page
allocation is in progress.  The locking is inherently unsafe for remote
access unless the CPU is hot-removed.

This series adjusts the locking.  A spinlock is added to struct
per_cpu_pages to protect the list contents while local_lock_irq continues
to prevent migration and IRQ reentry.  This allows a remote CPU to safely
drain a remote per-cpu list.

This series is a partial series.  Follow-on work should allow the
local_irq_save to be converted to a local_irq to avoid IRQs being
disabled/enabled in most cases.  Consequently, there are some TODO
comments highlighting the places that would change if local_irq was used. 
However, there are enough corner cases that it deserves a series on its
own separated by one kernel release and the priority right now is to avoid
interference of high priority tasks.

Patch 1 is a cosmetic patch to clarify when page->lru is storing buddy pages
	and when it is storing per-cpu pages.

Patch 2 shrinks per_cpu_pages to make room for a spin lock. Strictly speaking
	this is not necessary but it avoids per_cpu_pages consuming another
	cache line.

Patch 3 is a preparation patch to avoid code duplication.

Patch 4 is a simple micro-optimisation that improves code flow necessary for
	a later patch to avoid code duplication.

Patch 5 uses a spin_lock to protect the per_cpu_pages contents while still
	relying on local_lock to prevent migration, stabilise the pcp
	lookup and prevent IRQ reentrancy.

Patch 6 remote drains per-cpu pages directly instead of using a workqueue.


This patch (of 6):

The page allocator uses page->lru for storing pages on either buddy or PCP
lists.  Create page->buddy_list and page->pcp_list as a union with
page->lru.  This is simply to clarify what type of list a page is on in
the page allocator.

No functional change intended.

[minchan@kernel.org: fix page lru fields in macros]
Link: https://lkml.kernel.org/r/20220512085043.5234-1-mgorman@techsingularity.net
Link: https://lkml.kernel.org/r/20220512085043.5234-2-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Tested-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm_types.h |    5 +++++
 mm/page_alloc.c          |   24 ++++++++++++------------
 2 files changed, 17 insertions(+), 12 deletions(-)

--- a/include/linux/mm_types.h~mm-page_alloc-add-page-buddy_list-and-page-pcp_list
+++ a/include/linux/mm_types.h
@@ -88,6 +88,7 @@ struct page {
 			 */
 			union {
 				struct list_head lru;
+
 				/* Or, for the Unevictable "LRU list" slot */
 				struct {
 					/* Always even, to negate PageTail */
@@ -95,6 +96,10 @@ struct page {
 					/* Count page's or folio's mlocks */
 					unsigned int mlock_count;
 				};
+
+				/* Or, free page */
+				struct list_head buddy_list;
+				struct list_head pcp_list;
 			};
 			/* See page-flags.h for PAGE_MAPPING_FLAGS */
 			struct address_space *mapping;
--- a/mm/page_alloc.c~mm-page_alloc-add-page-buddy_list-and-page-pcp_list
+++ a/mm/page_alloc.c
@@ -781,7 +781,7 @@ static inline bool set_page_guard(struct
 		return false;
 
 	__SetPageGuard(page);
-	INIT_LIST_HEAD(&page->lru);
+	INIT_LIST_HEAD(&page->buddy_list);
 	set_page_private(page, order);
 	/* Guard pages are not available for any usage */
 	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
@@ -924,7 +924,7 @@ static inline void add_to_free_list(stru
 {
 	struct free_area *area = &zone->free_area[order];
 
-	list_add(&page->lru, &area->free_list[migratetype]);
+	list_add(&page->buddy_list, &area->free_list[migratetype]);
 	area->nr_free++;
 }
 
@@ -934,7 +934,7 @@ static inline void add_to_free_list_tail
 {
 	struct free_area *area = &zone->free_area[order];
 
-	list_add_tail(&page->lru, &area->free_list[migratetype]);
+	list_add_tail(&page->buddy_list, &area->free_list[migratetype]);
 	area->nr_free++;
 }
 
@@ -948,7 +948,7 @@ static inline void move_to_free_list(str
 {
 	struct free_area *area = &zone->free_area[order];
 
-	list_move_tail(&page->lru, &area->free_list[migratetype]);
+	list_move_tail(&page->buddy_list, &area->free_list[migratetype]);
 }
 
 static inline void del_page_from_free_list(struct page *page, struct zone *zone,
@@ -958,7 +958,7 @@ static inline void del_page_from_free_li
 	if (page_reported(page))
 		__ClearPageReported(page);
 
-	list_del(&page->lru);
+	list_del(&page->buddy_list);
 	__ClearPageBuddy(page);
 	set_page_private(page, 0);
 	zone->free_area[order].nr_free--;
@@ -1479,11 +1479,11 @@ static void free_pcppages_bulk(struct zo
 		do {
 			int mt;
 
-			page = list_last_entry(list, struct page, lru);
+			page = list_last_entry(list, struct page, pcp_list);
 			mt = get_pcppage_migratetype(page);
 
 			/* must delete to avoid corrupting pcp list */
-			list_del(&page->lru);
+			list_del(&page->pcp_list);
 			count -= nr_pages;
 			pcp->count -= nr_pages;
 
@@ -3043,7 +3043,7 @@ static int rmqueue_bulk(struct zone *zon
 		 * for IO devices that can merge IO requests if the physical
 		 * pages are ordered properly.
 		 */
-		list_add_tail(&page->lru, list);
+		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,
@@ -3293,7 +3293,7 @@ void mark_free_pages(struct zone *zone)
 
 	for_each_migratetype_order(order, t) {
 		list_for_each_entry(page,
-				&zone->free_area[order].free_list[t], lru) {
+				&zone->free_area[order].free_list[t], buddy_list) {
 			unsigned long i;
 
 			pfn = page_to_pfn(page);
@@ -3382,7 +3382,7 @@ static void free_unref_page_commit(struc
 	__count_vm_event(PGFREE);
 	pcp = this_cpu_ptr(zone->per_cpu_pageset);
 	pindex = order_to_pindex(migratetype, order);
-	list_add(&page->lru, &pcp->lists[pindex]);
+	list_add(&page->pcp_list, &pcp->lists[pindex]);
 	pcp->count += 1 << order;
 
 	/*
@@ -3645,8 +3645,8 @@ struct page *__rmqueue_pcplist(struct zo
 				return NULL;
 		}
 
-		page = list_first_entry(list, struct page, lru);
-		list_del(&page->lru);
+		page = list_first_entry(list, struct page, pcp_list);
+		list_del(&page->pcp_list);
 		pcp->count -= 1 << order;
 	} while (check_new_pcp(page, order));
 
_

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-page_alloc-add-page-buddy_list-and-page-pcp_list.patch
mm-page_alloc-use-only-one-pcp-list-for-thp-sized-allocations.patch
mm-page_alloc-split-out-buddy-removal-code-from-rmqueue-into-separate-helper.patch
mm-page_alloc-remove-unnecessary-page-==-null-check-in-rmqueue.patch
mm-page_alloc-protect-pcp-lists-with-a-spinlock.patch