linux-kernel - [PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler

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Message-Id: <20201210035526.38938-13-songmuchun@bytedance.com>
Date:   Thu, 10 Dec 2020 11:55:26 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        osalvador@...e.de, mhocko@...e.com, song.bao.hua@...ilicon.com,
        david@...hat.com
Cc:     duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler

We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 include/linux/hugetlb.h | 3 ++-
 mm/hugetlb_vmemmap.c    | 3 +++
 mm/hugetlb_vmemmap.h    | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 7295f6b3d55e..adc17765e0e9 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -791,7 +791,8 @@ 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)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 7f0b9e002be4..819ab9bb9298 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -208,6 +208,9 @@ bool hugetlb_free_vmemmap_enabled;
 
 static int __init early_hugetlb_free_vmemmap_param(char *buf)
 {
+	if (!is_power_of_2(sizeof(struct page)))
+		return 0;
+
 	if (!buf)
 		return -EINVAL;
 
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 0a1c0d33a316..5f5e90c81cd2 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -21,7 +21,7 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head);
  */
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
-	return h->nr_free_vmemmap_pages;
+	return h->nr_free_vmemmap_pages && is_power_of_2(sizeof(struct page));
 }
 #else
 static inline void hugetlb_vmemmap_init(struct hstate *h)
-- 
2.11.0