mm/page_alloc: ensure try_alloc_pages() plays well with unaccepted memory

JIRA: https://issues.redhat.com/browse/RHEL-78202

commit 23fa022
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date:   Tue May 6 14:25:08 2025 +0300

    mm/page_alloc: ensure try_alloc_pages() plays well with unaccepted memory

    try_alloc_pages() will not attempt to allocate memory if the system has
    *any* unaccepted memory.  Memory is accepted as needed and can remain in
    the system indefinitely, causing the interface to always fail.

    Rather than immediately giving up, attempt to use already accepted memory
    on free lists.

    Pass 'alloc_flags' to cond_accept_memory() and do not accept new memory
    for ALLOC_TRYLOCK requests.

    Found via code inspection - only BPF uses this at present and the
    runtime effects are unclear.

    Link: https://lkml.kernel.org/r/20250506112509.905147-2-kirill.shutemov@linux.intel.com
    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Fixes: 97769a5 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation")
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Suren Baghdasaryan <surenb@google.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Brendan Jackman <jackmanb@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Gregory Bell <grbell@redhat.com>

Author: Gbell26

mm/page_alloc.c

@@ -289,7 +289,8 @@ EXPORT_SYMBOL(nr_online_nodes);
 #endif
 
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
-static bool cond_accept_memory(struct zone *zone, unsigned int order);
+static bool cond_accept_memory(struct zone *zone, unsigned int order,
+			       int alloc_flags);
 static bool __free_unaccepted(struct page *page);
 
 int page_group_by_mobility_disabled __read_mostly;
@@ -3464,7 +3465,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 			}
 		}
 
-		cond_accept_memory(zone, order);
+		cond_accept_memory(zone, order, alloc_flags);
 
 		/*
 		 * Detect whether the number of free pages is below high
@@ -3491,7 +3492,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 				       gfp_mask)) {
 			int ret;
 
-			if (cond_accept_memory(zone, order))
+			if (cond_accept_memory(zone, order, alloc_flags))
 				goto try_this_zone;
 
 			/*
@@ -3544,7 +3545,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 
 			return page;
 		} else {
-			if (cond_accept_memory(zone, order))
+			if (cond_accept_memory(zone, order, alloc_flags))
 				goto try_this_zone;
 
 			/* Try again if zone has deferred pages */
@@ -4688,7 +4689,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 			goto failed;
 		}
 
-		cond_accept_memory(zone, 0);
+		cond_accept_memory(zone, 0, alloc_flags);
 retry_this_zone:
 		mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK) + nr_pages;
 		if (zone_watermark_fast(zone, 0,  mark,
@@ -4697,7 +4698,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 			break;
 		}
 
-		if (cond_accept_memory(zone, 0))
+		if (cond_accept_memory(zone, 0, alloc_flags))
 			goto retry_this_zone;
 
 		/* Try again if zone has deferred pages */
@@ -7063,7 +7064,8 @@ static inline bool has_unaccepted_memory(void)
 	return static_branch_unlikely(&zones_with_unaccepted_pages);
 }
 
-static bool cond_accept_memory(struct zone *zone, unsigned int order)
+static bool cond_accept_memory(struct zone *zone, unsigned int order,
+			       int alloc_flags)
 {
 	long to_accept, wmark;
 	bool ret = false;
@@ -7074,6 +7076,10 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order)
 	if (list_empty(&zone->unaccepted_pages))
 		return false;
 
+	/* Bailout, since try_to_accept_memory_one() needs to take a lock */
+	if (alloc_flags & ALLOC_TRYLOCK)
+		return false;
+
 	wmark = promo_wmark_pages(zone);
 
 	/*
@@ -7130,7 +7136,8 @@ static bool page_contains_unaccepted(struct page *page, unsigned int order)
 	return false;
 }
 
-static bool cond_accept_memory(struct zone *zone, unsigned int order)
+static bool cond_accept_memory(struct zone *zone, unsigned int order,
+			       int alloc_flags)
 {
 	return false;
 }
@@ -7201,11 +7208,6 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 	if (!pcp_allowed_order(order))
 		return NULL;
 
-#ifdef CONFIG_UNACCEPTED_MEMORY
-	/* Bailout, since try_to_accept_memory_one() needs to take a lock */
-	if (has_unaccepted_memory())
-		return NULL;
-#endif
 	/* Bailout, since _deferred_grow_zone() needs to take a lock */
 	if (deferred_pages_enabled())
 		return NULL;