[PATCH] mm/page_alloc: unify __alloc_frozen_pages[_nolock]_noprof()

[Brendan Jackman <jackmanb@google.com>]

Currently the core allocator code is controlled by ALLOC_NOLOCK, but the
main entry point function is significantly different from the normal
__alloc_frozen_pages_nolock(), this is tiring when reading the code.

Plumb the ALLOC_NOLOCK control one layer up in the call stack: create
an alloc_flags argument to __alloc_frozen_pages_nolock() (which is only
exposed to mm/) and then turn the nolock variant into a thin wrapper
that just sets that flag (as well as handling NUMA_NO_NODE, similar to
how some of the wrappers in gfp.h do).

Rationale that this doesn't change anything:

1. Simple bits: A bunch of the nolock-specific handling is just moved to
   the new alloc_order_allowed(), alloc_trylock_allowed() and
   gfp_trylock.

2. __alloc_frozen_pages_noprof() has some extra logic that wasn't
   previously in the nolock variant:

   a. Application of gfp_allowed_mask; this only affects early boot, and
      only flags that affect the slowpath get changed here.

   b. Application of current_gfp_context() - also only affects the
      slowpath

3. The slowpath itself: this is now just explicitly skipped under
   !ALLOC_TRYLOCK.

Ulterior motive: adding an alloc_flags arg to the allocator's
mm-internal entrypoint can later be used to do more allocation
customisation without needing to create new GFP flags.

No functional change intended.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 mm/hugetlb.c    |   2 +-
 mm/internal.h   |   4 +-
 mm/mempolicy.c  |   8 +--
 mm/page_alloc.c | 175 +++++++++++++++++++++++++++++---------------------------
 mm/slub.c       |   4 +-
 5 files changed, 99 insertions(+), 94 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 571212b80835e..619f6307dc98d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1806,7 +1806,7 @@ static struct folio *alloc_buddy_frozen_folio(int order, gfp_t gfp_mask,
 	if (alloc_try_hard)
 		gfp_mask |= __GFP_RETRY_MAYFAIL;
 
-	folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask);
+	folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask, 0);
 
 	/*
 	 * If we did not specify __GFP_RETRY_MAYFAIL, but still got a
diff --git a/mm/internal.h b/mm/internal.h
index 181e79f1d6a20..1043eb833836c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -913,7 +913,7 @@ extern bool free_pages_prepare(struct page *page, unsigned int order);
 extern int user_min_free_kbytes;
 
 struct page *__alloc_frozen_pages_noprof(gfp_t, unsigned int order, int nid,
-		nodemask_t *);
+		nodemask_t *, unsigned int alloc_flags);
 #define __alloc_frozen_pages(...) \
 	alloc_hooks(__alloc_frozen_pages_noprof(__VA_ARGS__))
 void free_frozen_pages(struct page *page, unsigned int order);
@@ -924,7 +924,7 @@ struct page *alloc_frozen_pages_noprof(gfp_t, unsigned int order);
 #else
 static inline struct page *alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order)
 {
-	return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL);
+	return __alloc_frozen_pages_noprof(gfp, order, numa_node_id(), NULL, 0);
 }
 #endif
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 36699fabd3c22..dccff90682035 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2425,9 +2425,9 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
 	 */
 	preferred_gfp = gfp | __GFP_NOWARN;
 	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
-	page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask);
+	page = __alloc_frozen_pages_noprof(preferred_gfp, order, nid, nodemask, 0);
 	if (!page)
-		page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL);
+		page = __alloc_frozen_pages_noprof(gfp, order, nid, NULL, 0);
 
 	return page;
 }
@@ -2475,7 +2475,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 			 */
 			page = __alloc_frozen_pages_noprof(
 				gfp | __GFP_THISNODE | __GFP_NORETRY, order,
-				nid, NULL);
+				nid, NULL, 0);
 			if (page || !(gfp & __GFP_DIRECT_RECLAIM))
 				return page;
 			/*
@@ -2487,7 +2487,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,
 		}
 	}
 
-	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask);
+	page = __alloc_frozen_pages_noprof(gfp, order, nid, nodemask, 0);
 
 	if (unlikely(pol->mode == MPOL_INTERLEAVE ||
 		     pol->mode == MPOL_WEIGHTED_INTERLEAVE) && page) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0111cdbdb5321..fc4d07bbf44b5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5253,24 +5253,98 @@ void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
 	}
 }
 
-/*
- * This is the 'heart' of the zoned buddy allocator.
- */
-struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
-		int preferred_nid, nodemask_t *nodemask)
+static inline bool alloc_order_allowed(gfp_t gfp, unsigned int order,
+				       unsigned int alloc_flags)
 {
-	struct page *page;
-	unsigned int alloc_flags = ALLOC_WMARK_LOW;
-	gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
-	struct alloc_context ac = { };
+
+	if (alloc_flags & ALLOC_TRYLOCK)
+		return pcp_allowed_order(order);
 
 	/*
 	 * There are several places where we assume that the order value is sane
 	 * so bail out early if the request is out of bound.
 	 */
-	if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
+	return !(WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp));
+}
+
+static inline bool alloc_trylock_allowed(void)
+{
+	/*
+	 * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is
+	 * unsafe in NMI. If spin_trylock() is called from hard IRQ the current
+	 * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will
+	 * mark the task as the owner of another rt_spin_lock which will
+	 * confuse PI logic, so return immediately if called from hard IRQ or
+	 * NMI.
+	 *
+	 * Note, irqs_disabled() case is ok. This function can be called
+	 * from raw_spin_lock_irqsave region.
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
+		return false;
+
+	/* On UP, spin_trylock() always succeeds even when it is locked */
+	if (!IS_ENABLED(CONFIG_SMP) && in_nmi())
+		return false;
+
+	/* Bailout, since _deferred_grow_zone() needs to take a lock */
+	if (deferred_pages_enabled())
+		return false;
+
+	return true;
+}
+
+/*
+ * GFP flags to set for ALLOC_TRYLOCK i.e. alloc_pages_nolock().
+ *
+ * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
+ * Do not specify __GFP_KSWAPD_RECLAIM either, since wake up of kswapd
+ * is not safe in arbitrary context.
+ *
+ * These two are the conditions for gfpflags_allow_spinning() being true.
+ *
+ * Specify __GFP_NOWARN since failing alloc_pages_nolock() is not a reason
+ * to warn. Also warn would trigger printk() which is unsafe from
+ * various contexts. We cannot use printk_deferred_enter() to mitigate,
+ * since the running context is unknown.
+ *
+ * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below
+ * is safe in any context. Also zeroing the page is mandatory for
+ * BPF use cases.
+ *
+ * Though __GFP_NOMEMALLOC is not checked in the code path below,
+ * specify it here to highlight that alloc_pages_nolock()
+ * doesn't want to deplete reserves.
+ */
+static const gfp_t gfp_trylock = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC |
+				__GFP_COMP;
+
+/*
+ * This is the 'heart' of the zoned buddy allocator.
+ */
+struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
+		int preferred_nid, nodemask_t *nodemask, unsigned int alloc_flags)
+{
+	struct page *page;
+	gfp_t alloc_gfp; /* The gfp_t that was actually used for allocation */
+	struct alloc_context ac = { };
+
+	/* Other flags could be supported later if needed. */
+	if (WARN_ON(alloc_flags & ~ALLOC_TRYLOCK))
 		return NULL;
 
+	if (!alloc_order_allowed(gfp, order, alloc_flags))
+		return NULL;
+
+	if (alloc_flags & ALLOC_TRYLOCK) {
+		VM_WARN_ON_ONCE(gfp & ~__GFP_ACCOUNT);
+		if (!alloc_trylock_allowed())
+			return NULL;
+		gfp |= gfp_trylock;
+	} else {
+		alloc_flags |= ALLOC_WMARK_LOW;
+	}
+
 	gfp &= gfp_allowed_mask;
 	/*
 	 * Apply scoped allocation constraints. This is mainly about GFP_NOFS
@@ -5291,9 +5365,9 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
 	 */
 	alloc_flags |= alloc_flags_nofragment(zonelist_zone(ac.preferred_zoneref), gfp);
 
-	/* First allocation attempt */
+	/* First allocation attempt (or, for trylock, only attempt) */
 	page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);
-	if (likely(page))
+	if (likely(page) || (alloc_flags & ALLOC_TRYLOCK))
 		goto out;
 
 	alloc_gfp = gfp;
@@ -5310,7 +5384,8 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
 out:
 	if (memcg_kmem_online() && (gfp & __GFP_ACCOUNT) && page &&
 	    unlikely(__memcg_kmem_charge_page(page, gfp, order) != 0)) {
-		free_frozen_pages(page, order);
+		__free_frozen_pages(page, order,
+				    alloc_flags & ALLOC_TRYLOCK ? FPI_TRYLOCK : 0);
 		page = NULL;
 	}
 
@@ -5326,7 +5401,7 @@ struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
 {
 	struct page *page;
 
-	page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask);
+	page = __alloc_frozen_pages_noprof(gfp, order, preferred_nid, nodemask, 0);
 	if (page)
 		set_page_refcounted(page);
 	return page;
@@ -7856,80 +7931,10 @@ static bool __free_unaccepted(struct page *page)
 
 struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned int order)
 {
-	/*
-	 * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
-	 * Do not specify __GFP_KSWAPD_RECLAIM either, since wake up of kswapd
-	 * is not safe in arbitrary context.
-	 *
-	 * These two are the conditions for gfpflags_allow_spinning() being true.
-	 *
-	 * Specify __GFP_NOWARN since failing alloc_pages_nolock() is not a reason
-	 * to warn. Also warn would trigger printk() which is unsafe from
-	 * various contexts. We cannot use printk_deferred_enter() to mitigate,
-	 * since the running context is unknown.
-	 *
-	 * Specify __GFP_ZERO to make sure that call to kmsan_alloc_page() below
-	 * is safe in any context. Also zeroing the page is mandatory for
-	 * BPF use cases.
-	 *
-	 * Though __GFP_NOMEMALLOC is not checked in the code path below,
-	 * specify it here to highlight that alloc_pages_nolock()
-	 * doesn't want to deplete reserves.
-	 */
-	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC | __GFP_COMP
-			| gfp_flags;
-	unsigned int alloc_flags = ALLOC_TRYLOCK;
-	struct alloc_context ac = { };
-	struct page *page;
-
-	VM_WARN_ON_ONCE(gfp_flags & ~__GFP_ACCOUNT);
-	/*
-	 * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is
-	 * unsafe in NMI. If spin_trylock() is called from hard IRQ the current
-	 * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will
-	 * mark the task as the owner of another rt_spin_lock which will
-	 * confuse PI logic, so return immediately if called from hard IRQ or
-	 * NMI.
-	 *
-	 * Note, irqs_disabled() case is ok. This function can be called
-	 * from raw_spin_lock_irqsave region.
-	 */
-	if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
-		return NULL;
-
-	/* On UP, spin_trylock() always succeeds even when it is locked */
-	if (!IS_ENABLED(CONFIG_SMP) && in_nmi())
-		return NULL;
-
-	if (!pcp_allowed_order(order))
-		return NULL;
-
-	/* Bailout, since _deferred_grow_zone() needs to take a lock */
-	if (deferred_pages_enabled())
-		return NULL;
-
 	if (nid == NUMA_NO_NODE)
 		nid = numa_node_id();
 
-	prepare_alloc_pages(alloc_gfp, order, nid, NULL, &ac,
-			    &alloc_gfp, &alloc_flags);
-
-	/*
-	 * Best effort allocation from percpu free list.
-	 * If it's empty attempt to spin_trylock zone->lock.
-	 */
-	page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac);
-
-	/* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */
-
-	if (memcg_kmem_online() && page && (gfp_flags & __GFP_ACCOUNT) &&
-	    unlikely(__memcg_kmem_charge_page(page, alloc_gfp, order) != 0)) {
-		__free_frozen_pages(page, order, FPI_TRYLOCK);
-		page = NULL;
-	}
-	trace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);
-	kmsan_alloc_page(page, order, alloc_gfp);
-	return page;
+	return __alloc_frozen_pages_noprof(gfp_flags, order, nid, NULL, ALLOC_TRYLOCK);
 }
 /**
  * alloc_pages_nolock - opportunistic reentrant allocation from any context
diff --git a/mm/slub.c b/mm/slub.c
index a2bf3756ca7d0..b9fb66071bd07 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3275,7 +3275,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
 	else if (node == NUMA_NO_NODE)
 		page = alloc_frozen_pages(flags, order);
 	else
-		page = __alloc_frozen_pages(flags, order, node, NULL);
+		page = __alloc_frozen_pages(flags, order, node, NULL, 0);
 
 	if (!page)
 		return NULL;
@@ -5236,7 +5236,7 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
 	if (node == NUMA_NO_NODE)
 		page = alloc_frozen_pages_noprof(flags, order);
 	else
-		page = __alloc_frozen_pages_noprof(flags, order, node, NULL);
+		page = __alloc_frozen_pages_noprof(flags, order, node, NULL, 0);
 
 	if (page) {
 		ptr = page_address(page);

---
base-commit: 1111012ec6508a38a39f8d20c213c8c9cf3c96c0
change-id: 20260617-alloc-trylock-14ad37dab337

Best regards,
--  
Brendan Jackman <jackmanb@google.com>