mm: rename try_alloc_pages() to alloc_pages_nolock()

The "try_" prefix is confusing, since it made people believe that
try_alloc_pages() is analogous to spin_trylock() and NULL return means
EAGAIN.  This is not the case.  If it returns NULL there is no reason to
call it again.  It will most likely return NULL again.  Hence rename it to
alloc_pages_nolock() to make it symmetrical to free_pages_nolock() and
document that NULL means ENOMEM.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Harry Yoo <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Kumar Kartikeya Dwivedi <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Alexei Starovoitov

include/linux/gfp.h

@@ -45,13 +45,13 @@ static inline bool gfpflags_allow_spinning(const gfp_t gfp_flags)
 	 * !__GFP_DIRECT_RECLAIM -> direct claim is not allowed.
 	 * !__GFP_KSWAPD_RECLAIM -> it's not safe to wake up kswapd.
 	 * All GFP_* flags including GFP_NOWAIT use one or both flags.
-	 * try_alloc_pages() is the only API that doesn't specify either flag.
+	 * alloc_pages_nolock() is the only API that doesn't specify either flag.
 	 *
 	 * This is stronger than GFP_NOWAIT or GFP_ATOMIC because
 	 * those are guaranteed to never block on a sleeping lock.
 	 * Here we are enforcing that the allocation doesn't ever spin
 	 * on any locks (i.e. only trylocks). There is no high level
-	 * GFP_$FOO flag for this use in try_alloc_pages() as the
+	 * GFP_$FOO flag for this use in alloc_pages_nolock() as the
 	 * regular page allocator doesn't fully support this
 	 * allocation mode.
 	 */
@@ -354,8 +354,8 @@ static inline struct page *alloc_page_vma_noprof(gfp_t gfp,
 }
 #define alloc_page_vma(...)			alloc_hooks(alloc_page_vma_noprof(__VA_ARGS__))
 
-struct page *try_alloc_pages_noprof(int nid, unsigned int order);
-#define try_alloc_pages(...)			alloc_hooks(try_alloc_pages_noprof(__VA_ARGS__))
+struct page *alloc_pages_nolock_noprof(int nid, unsigned int order);
+#define alloc_pages_nolock(...)			alloc_hooks(alloc_pages_nolock_noprof(__VA_ARGS__))
 
 extern unsigned long get_free_pages_noprof(gfp_t gfp_mask, unsigned int order);
 #define __get_free_pages(...)			alloc_hooks(get_free_pages_noprof(__VA_ARGS__))

kernel/bpf/syscall.c

@@ -578,7 +578,7 @@ static bool can_alloc_pages(void)
 static struct page *__bpf_alloc_page(int nid)
 {
 	if (!can_alloc_pages())
-		return try_alloc_pages(nid, 0);
+		return alloc_pages_nolock(nid, 0);
 
 	return alloc_pages_node(nid,
 				GFP_KERNEL | __GFP_ZERO | __GFP_ACCOUNT

mm/page_alloc.c

@@ -5070,7 +5070,7 @@ EXPORT_SYMBOL(__free_pages);
 
 /*
  * Can be called while holding raw_spin_lock or from IRQ and NMI for any
- * page type (not only those that came from try_alloc_pages)
+ * page type (not only those that came from alloc_pages_nolock)
  */
 void free_pages_nolock(struct page *page, unsigned int order)
 {
@@ -7311,20 +7311,21 @@ static bool __free_unaccepted(struct page *page)
 #endif /* CONFIG_UNACCEPTED_MEMORY */
 
 /**
- * try_alloc_pages - opportunistic reentrant allocation from any context
+ * alloc_pages_nolock - opportunistic reentrant allocation from any context
  * @nid: node to allocate from
  * @order: allocation order size
  *
  * Allocates pages of a given order from the given node. This is safe to
  * call from any context (from atomic, NMI, and also reentrant
- * allocator -> tracepoint -> try_alloc_pages_noprof).
+ * allocator -> tracepoint -> alloc_pages_nolock_noprof).
  * Allocation is best effort and to be expected to fail easily so nobody should
  * rely on the success. Failures are not reported via warn_alloc().
  * See always fail conditions below.
  *
- * Return: allocated page or NULL on failure.
+ * Return: allocated page or NULL on failure. NULL does not mean EBUSY or EAGAIN.
+ * It means ENOMEM. There is no reason to call it again and expect !NULL.
  */
-struct page *try_alloc_pages_noprof(int nid, unsigned int order)
+struct page *alloc_pages_nolock_noprof(int nid, unsigned int order)
 {
 	/*
 	 * Do not specify __GFP_DIRECT_RECLAIM, since direct claim is not allowed.
@@ -7333,7 +7334,7 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 	 *
 	 * These two are the conditions for gfpflags_allow_spinning() being true.
 	 *
-	 * Specify __GFP_NOWARN since failing try_alloc_pages() is not a reason
+	 * 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.
@@ -7343,7 +7344,7 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 	 * BPF use cases.
 	 *
 	 * Though __GFP_NOMEMALLOC is not checked in the code path below,
-	 * specify it here to highlight that try_alloc_pages()
+	 * 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

mm/page_owner.c

@@ -302,7 +302,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
 	/*
 	 * Do not specify GFP_NOWAIT to make gfpflags_allow_spinning() == false
 	 * to prevent issues in stack_depot_save().
-	 * This is similar to try_alloc_pages() gfp flags, but only used
+	 * This is similar to alloc_pages_nolock() gfp flags, but only used
 	 * to signal stack_depot to avoid spin_locks.
 	 */
 	handle = save_stack(__GFP_NOWARN);