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From: Alexandru Elisei <alexandru.elisei@arm.com>
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Subject: [PATCH RFC v3 10/35] mm: cma: Fast track allocating memory when the pages are free
Date: Thu, 25 Jan 2024 16:42:31 +0000
Message-Id: <20240125164256.4147-11-alexandru.elisei@arm.com>
In-Reply-To: <20240125164256.4147-1-alexandru.elisei@arm.com>
References: <20240125164256.4147-1-alexandru.elisei@arm.com>
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If the pages to be allocated are free, take them directly off the buddy
allocator, instead of going through alloc_contig_range() and avoiding
costly calls to lru_cache_disable().

Only allocations of the same size as the CMA region order are considered,
to avoid taking the zone spinlock for too long.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---

Changes since rfc v2:

* New patch. Reworked from the rfc v2 patch #26 ("arm64: mte: Fast track
reserving tag storage when the block is free") (David Hildenbrand).

 include/linux/page-flags.h | 15 ++++++++++++--
 mm/Kconfig                 |  5 +++++
 mm/cma.c                   | 42 ++++++++++++++++++++++++++++++++++----
 mm/memory-failure.c        |  8 ++++----
 mm/page_alloc.c            | 23 ++++++++++++---------
 5 files changed, 73 insertions(+), 20 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 735cddc13d20..b7237bce7446 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -575,11 +575,22 @@ TESTSCFLAG(HWPoison, hwpoison, PF_ANY)
 #define MAGIC_HWPOISON	0x48575053U	/* HWPS */
 extern void SetPageHWPoisonTakenOff(struct page *page);
 extern void ClearPageHWPoisonTakenOff(struct page *page);
-extern bool take_page_off_buddy(struct page *page);
-extern bool put_page_back_buddy(struct page *page);
+extern bool PageHWPoisonTakenOff(struct page *page);
 #else
 PAGEFLAG_FALSE(HWPoison, hwpoison)
+TESTSCFLAG_FALSE(HWPoison, hwpoison)
 #define __PG_HWPOISON 0
+static inline void SetPageHWPoisonTakenOff(struct page *page) { }
+static inline void ClearPageHWPoisonTakenOff(struct page *page) { }
+static inline bool PageHWPoisonTakenOff(struct page *page)
+{
+      return false;
+}
+#endif
+
+#ifdef CONFIG_WANTS_TAKE_PAGE_OFF_BUDDY
+extern bool take_page_off_buddy(struct page *page, bool poison);
+extern bool put_page_back_buddy(struct page *page, bool unpoison);
 #endif
 
 #if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
diff --git a/mm/Kconfig b/mm/Kconfig
index ffc3a2ba3a8c..341cf53898db 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -745,12 +745,16 @@ config DEFAULT_MMAP_MIN_ADDR
 config ARCH_SUPPORTS_MEMORY_FAILURE
 	bool
 
+config WANTS_TAKE_PAGE_OFF_BUDDY
+	bool
+
 config MEMORY_FAILURE
 	depends on MMU
 	depends on ARCH_SUPPORTS_MEMORY_FAILURE
 	bool "Enable recovery from hardware memory errors"
 	select MEMORY_ISOLATION
 	select RAS
+	select WANTS_TAKE_PAGE_OFF_BUDDY
 	help
 	  Enables code to recover from some memory failures on systems
 	  with MCA recovery. This allows a system to continue running
@@ -891,6 +895,7 @@ config CMA
 	depends on MMU
 	select MIGRATION
 	select MEMORY_ISOLATION
+	select WANTS_TAKE_PAGE_OFF_BUDDY
 	help
 	  This enables the Contiguous Memory Allocator which allows other
 	  subsystems to allocate big physically-contiguous blocks of memory.
diff --git a/mm/cma.c b/mm/cma.c
index 2881bab12b01..15663f95d77b 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -444,6 +444,34 @@ static void cma_debug_show_areas(struct cma *cma)
 static inline void cma_debug_show_areas(struct cma *cma) { }
 #endif
 
+/* Called with the cma mutex held. */
+static int cma_alloc_pages_fastpath(struct cma *cma, unsigned long start,
+				    unsigned long end)
+{
+	bool success = false;
+	unsigned long i, j;
+
+	/* Avoid contention on the zone lock. */
+	if (start - end != 1 << cma->order_per_bit)
+		return -EINVAL;
+
+	for (i = start; i < end; i++) {
+		if (!is_free_buddy_page(pfn_to_page(i)))
+			break;
+		success = take_page_off_buddy(pfn_to_page(i), false);
+		if (!success)
+			break;
+	}
+
+	if (success)
+		return 0;
+
+	for (j = start; j < i; j++)
+		put_page_back_buddy(pfn_to_page(j), false);
+
+	return -EBUSY;
+}
+
 /**
  * cma_alloc_range() - allocate pages in a specific range
  * @cma:   Contiguous memory region for which the allocation is performed.
@@ -493,7 +521,11 @@ int cma_alloc_range(struct cma *cma, unsigned long start, unsigned long count,
 
 	for (i = 0; i < tries; i++) {
 		mutex_lock(&cma_mutex);
-		err = alloc_contig_range(start, start + count, MIGRATE_CMA, gfp);
+		err = cma_alloc_pages_fastpath(cma, start, start + count);
+		if (err) {
+			err = alloc_contig_range(start, start + count,
+						 MIGRATE_CMA, gfp);
+		}
 		mutex_unlock(&cma_mutex);
 
 		if (err != -EBUSY)
@@ -529,7 +561,6 @@ int cma_alloc_range(struct cma *cma, unsigned long start, unsigned long count,
 	return err;
 }
 
-
 /**
  * cma_alloc() - allocate pages from contiguous area
  * @cma:   Contiguous memory region for which the allocation is performed.
@@ -589,8 +620,11 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 
 		pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit);
 		mutex_lock(&cma_mutex);
-		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
-				     GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
+		ret = cma_alloc_pages_fastpath(cma, pfn, pfn + count);
+		if (ret) {
+			ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
+					GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
+		}
 		mutex_unlock(&cma_mutex);
 		if (ret == 0) {
 			page = pfn_to_page(pfn);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4f9b61f4a668..b87b533a9871 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -157,7 +157,7 @@ static int __page_handle_poison(struct page *page)
 	zone_pcp_disable(page_zone(page));
 	ret = dissolve_free_huge_page(page);
 	if (!ret)
-		ret = take_page_off_buddy(page);
+		ret = take_page_off_buddy(page, true);
 	zone_pcp_enable(page_zone(page));
 
 	return ret;
@@ -1353,7 +1353,7 @@ static int page_action(struct page_state *ps, struct page *p,
 	return action_result(pfn, ps->type, result);
 }
 
-static inline bool PageHWPoisonTakenOff(struct page *page)
+bool PageHWPoisonTakenOff(struct page *page)
 {
 	return PageHWPoison(page) && page_private(page) == MAGIC_HWPOISON;
 }
@@ -2247,7 +2247,7 @@ int memory_failure(unsigned long pfn, int flags)
 		res = get_hwpoison_page(p, flags);
 		if (!res) {
 			if (is_free_buddy_page(p)) {
-				if (take_page_off_buddy(p)) {
+				if (take_page_off_buddy(p, true)) {
 					page_ref_inc(p);
 					res = MF_RECOVERED;
 				} else {
@@ -2578,7 +2578,7 @@ int unpoison_memory(unsigned long pfn)
 		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
 	} else if (ghp < 0) {
 		if (ghp == -EHWPOISON) {
-			ret = put_page_back_buddy(p) ? 0 : -EBUSY;
+			ret = put_page_back_buddy(p, true) ? 0 : -EBUSY;
 		} else {
 			ret = ghp;
 			unpoison_pr_info("Unpoison: failed to grab page %#lx\n",
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0fa34bcfb1af..502ee3eb8583 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6655,7 +6655,7 @@ bool is_free_buddy_page(struct page *page)
 }
 EXPORT_SYMBOL(is_free_buddy_page);
 
-#ifdef CONFIG_MEMORY_FAILURE
+#ifdef CONFIG_WANTS_TAKE_PAGE_OFF_BUDDY
 /*
  * Break down a higher-order page in sub-pages, and keep our target out of
  * buddy allocator.
@@ -6687,9 +6687,9 @@ static void break_down_buddy_pages(struct zone *zone, struct page *page,
 }
 
 /*
- * Take a page that will be marked as poisoned off the buddy allocator.
+ * Take a page off the buddy allocator, and optionally mark it as poisoned.
  */
-bool take_page_off_buddy(struct page *page)
+bool take_page_off_buddy(struct page *page, bool poison)
 {
 	struct zone *zone = page_zone(page);
 	unsigned long pfn = page_to_pfn(page);
@@ -6710,7 +6710,8 @@ bool take_page_off_buddy(struct page *page)
 			del_page_from_free_list(page_head, zone, page_order);
 			break_down_buddy_pages(zone, page_head, page, 0,
 						page_order, migratetype);
-			SetPageHWPoisonTakenOff(page);
+			if (poison)
+				SetPageHWPoisonTakenOff(page);
 			if (!is_migrate_isolate(migratetype))
 				__mod_zone_freepage_state(zone, -1, migratetype);
 			ret = true;
@@ -6724,9 +6725,10 @@ bool take_page_off_buddy(struct page *page)
 }
 
 /*
- * Cancel takeoff done by take_page_off_buddy().
+ * Cancel takeoff done by take_page_off_buddy(), and optionally unpoison the
+ * page.
  */
-bool put_page_back_buddy(struct page *page)
+bool put_page_back_buddy(struct page *page, bool unpoison)
 {
 	struct zone *zone = page_zone(page);
 	unsigned long pfn = page_to_pfn(page);
@@ -6736,17 +6738,18 @@ bool put_page_back_buddy(struct page *page)
 
 	spin_lock_irqsave(&zone->lock, flags);
 	if (put_page_testzero(page)) {
-		ClearPageHWPoisonTakenOff(page);
+		VM_WARN_ON_ONCE(PageHWPoisonTakenOff(page) && !unpoison);
+		if (unpoison)
+			ClearPageHWPoisonTakenOff(page);
 		__free_one_page(page, pfn, zone, 0, migratetype, FPI_NONE);
-		if (TestClearPageHWPoison(page)) {
+		if (!unpoison || (unpoison && TestClearPageHWPoison(page)))
 			ret = true;
-		}
 	}
 	spin_unlock_irqrestore(&zone->lock, flags);
 
 	return ret;
 }
-#endif
+#endif /* CONFIG_WANTS_TAKE_PAGE_OFF_BUDDY */
 
 #ifdef CONFIG_ZONE_DMA
 bool has_managed_dma(void)
-- 
2.43.0