+ mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch added to -mm tree

+ mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: hugetlb: optimize the code with the help of the compiler
has been added to the -mm tree.  Its filename is
     mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: hugetlb: optimize the code with the help of the compiler

When the "struct page size" crosses page boundaries we cannot make use of
this feature.  Let free_vmemmap_pages_per_hpage() return zero if that is
the case, most of the functions can be optimized away.

Link: https://lkml.kernel.org/r/20210308102807.59745-10-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Barry Song <song.bao.hua@hisilicon.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oliver Neukum <oneukum@suse.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/hugetlb.h |    3 ++-
 mm/hugetlb_vmemmap.c    |    7 +++++++
 mm/hugetlb_vmemmap.h    |    6 ++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

--- a/include/linux/hugetlb.h~mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler
+++ a/include/linux/hugetlb.h
@@ -894,7 +894,8 @@ extern bool hugetlb_free_vmemmap_enabled
 
 static inline bool is_hugetlb_free_vmemmap_enabled(void)
 {
-	return hugetlb_free_vmemmap_enabled;
+	return hugetlb_free_vmemmap_enabled &&
+	       is_power_of_2(sizeof(struct page));
 }
 #else
 static inline bool is_hugetlb_free_vmemmap_enabled(void)
--- a/mm/hugetlb_vmemmap.c~mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler
+++ a/mm/hugetlb_vmemmap.c
@@ -265,6 +265,13 @@ void __init hugetlb_vmemmap_init(struct
 	BUILD_BUG_ON(__NR_USED_SUBPAGE >=
 		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
 
+	/*
+	 * The compiler can help us to optimize this function to null
+	 * when the size of the struct page is not power of 2.
+	 */
+	if (!is_power_of_2(sizeof(struct page)))
+		return;
+
 	if (!hugetlb_free_vmemmap_enabled)
 		return;
 
--- a/mm/hugetlb_vmemmap.h~mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler
+++ a/mm/hugetlb_vmemmap.h
@@ -21,6 +21,12 @@ void hugetlb_vmemmap_init(struct hstate
  */
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
+	/*
+	 * This check aims to let the compiler help us optimize the code as
+	 * much as possible.
+	 */
+	if (!is_power_of_2(sizeof(struct page)))
+		return 0;
 	return h->nr_free_vmemmap_pages;
 }
 #else
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-memcontrol-fix-kernel-stack-account.patch
mm-memory_hotplug-factor-out-bootmem-core-functions-to-bootmem_infoc.patch
mm-hugetlb-introduce-a-new-config-hugetlb_page_free_vmemmap.patch
mm-hugetlb-free-the-vmemmap-pages-associated-with-each-hugetlb-page.patch
mm-hugetlb-alloc-the-vmemmap-pages-associated-with-each-hugetlb-page.patch
mm-hugetlb-set-the-pagehwpoison-to-the-raw-error-page.patch
mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap.patch
mm-hugetlb-introduce-nr_free_vmemmap_pages-in-the-struct-hstate.patch
mm-hugetlb-gather-discrete-indexes-of-tail-page.patch
mm-hugetlb-optimize-the-code-with-the-help-of-the-compiler.patch