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From: Gang Li <gang.li@linux.dev>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>,
	David Rientjes <rientjes@google.com>,
	Muchun Song <muchun.song@linux.dev>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Steffen Klassert <steffen.klassert@secunet.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	Jane Chu <jane.chu@oracle.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	ligang.bdlg@bytedance.com,
	Gang Li <gang.li@linux.dev>
Subject: [PATCH v6 5/8] padata: downgrade padata_do_multithreaded to serial execution for non-SMP
Date: Thu, 22 Feb 2024 22:04:18 +0800
Message-Id: <20240222140422.393911-6-gang.li@linux.dev>
In-Reply-To: <20240222140422.393911-1-gang.li@linux.dev>
References: <20240222140422.393911-1-gang.li@linux.dev>
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hugetlb parallelization depends on PADATA, and PADATA depends on SMP.

PADATA consists of two distinct functionality: One part is
padata_do_multithreaded which disregards order and simply divides
tasks into several groups for parallel execution. Hugetlb
init parallelization depends on padata_do_multithreaded.

The other part is composed of a set of APIs that, while handling data in
an out-of-order parallel manner, can eventually return the data with
ordered sequence. Currently Only `crypto/pcrypt.c` use them.

All users of PADATA of non-SMP case currently only use
padata_do_multithreaded. It is easy to implement a serial one in
include/linux/padata.h. And it is not necessary to implement another
functionality unless the only user of crypto/pcrypt.c does not depend on
SMP in the future.

Signed-off-by: Gang Li <ligang.bdlg@bytedance.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/padata.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/padata.h b/include/linux/padata.h
index 8f418711351bc..0146daf344306 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -180,10 +180,6 @@ struct padata_instance {
 
 #ifdef CONFIG_PADATA
 extern void __init padata_init(void);
-#else
-static inline void __init padata_init(void) {}
-#endif
-
 extern struct padata_instance *padata_alloc(const char *name);
 extern void padata_free(struct padata_instance *pinst);
 extern struct padata_shell *padata_alloc_shell(struct padata_instance *pinst);
@@ -194,4 +190,12 @@ extern void padata_do_serial(struct padata_priv *padata);
 extern void __init padata_do_multithreaded(struct padata_mt_job *job);
 extern int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
 			      cpumask_var_t cpumask);
+#else
+static inline void __init padata_init(void) {}
+static inline void __init padata_do_multithreaded(struct padata_mt_job *job)
+{
+	job->thread_fn(job->start, job->start + job->size, job->fn_arg);
+}
+#endif
+
 #endif
-- 
2.20.1