[PATCH RFC v3 10/35] mm: cma: Fast track allocating memory when the pages are free

Alexandru Elisei
2024-01-25T16:45:47Z

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