From: Muchun Song <songmuchun@bytedance.com>
To: Michal Hocko <mhocko@suse.com>
Cc: "Jonathan Corbet" <corbet@lwn.net>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
bp@alien8.de, x86@kernel.org, hpa@zytor.com,
dave.hansen@linux.intel.com, luto@kernel.org,
"Peter Zijlstra" <peterz@infradead.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
paulmck@kernel.org, mchehab+huawei@kernel.org,
pawan.kumar.gupta@linux.intel.com,
"Randy Dunlap" <rdunlap@infradead.org>,
oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
"Mina Almasry" <almasrymina@google.com>,
"David Rientjes" <rientjes@google.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Oscar Salvador" <osalvador@suse.de>,
"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
"David Hildenbrand" <david@redhat.com>,
"HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
"Joao Martins" <joao.m.martins@oracle.com>,
"Xiongchun duan" <duanxiongchun@bytedance.com>,
linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
"Linux Memory Management List" <linux-mm@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"Miaohe Lin" <linmiaohe@huawei.com>,
"Chen Huang" <chenhuang5@huawei.com>,
"Bodeddula Balasubramaniam" <bodeddub@amazon.com>
Subject: Re: [External] Re: [PATCH v18 9/9] mm: hugetlb: optimize the code with the help of the compiler
Date: Thu, 11 Mar 2021 15:33:20 +0800 [thread overview]
Message-ID: <CAMZfGtV1Fp1RiQ64c9RrMmZ+=EwjGRHjwL8Wx3Q0YRWbbKF6xg@mail.gmail.com> (raw)
In-Reply-To: <YEjoozshsvKeMAAu@dhcp22.suse.cz>
On Wed, Mar 10, 2021 at 11:41 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 08-03-21 18:28:07, Muchun Song wrote:
> > 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.
>
> I am confused. Don't you check for this in early_hugetlb_free_vmemmap_param already?
Right.
> Why do we need any runtime checks?
If the size of the struct page is not power of 2, compiler can think
is_hugetlb_free_vmemmap_enabled() always return false. So
the code snippet of this user can be optimized away.
E.g.
if (is_hugetlb_free_vmemmap_enabled())
/* do something */
The compiler can drop "/* do something */" directly, because
it knows is_hugetlb_free_vmemmap_enabled() always returns
false.
Thanks.
>
> > 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>
> > ---
> > include/linux/hugetlb.h | 3 ++-
> > mm/hugetlb_vmemmap.c | 7 +++++++
> > mm/hugetlb_vmemmap.h | 6 ++++++
> > 3 files changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index c70421e26189..333dd0479fc2 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -880,7 +880,8 @@ 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 33e42678abe3..1ba1ef45c48c 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -265,6 +265,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> > 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;
> >
> > diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> > index cb2bef8f9e73..29aaaf7b741e 100644
> > --- a/mm/hugetlb_vmemmap.h
> > +++ b/mm/hugetlb_vmemmap.h
> > @@ -21,6 +21,12 @@ void hugetlb_vmemmap_init(struct hstate *h);
> > */
> > 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
> > --
> > 2.11.0
> >
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2021-03-11 7:34 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 10:27 [PATCH v18 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-03-08 10:27 ` [PATCH v18 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-03-10 14:14 ` Michal Hocko
2021-03-11 2:58 ` [External] " Muchun Song
2021-03-11 8:45 ` Muchun Song
2021-03-11 8:53 ` Michal Hocko
2021-03-11 9:05 ` Muchun Song
2021-03-08 10:28 ` [PATCH v18 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-03-08 10:28 ` [PATCH v18 3/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-03-10 14:32 ` Michal Hocko
2021-03-11 3:35 ` [External] " Muchun Song
2021-03-08 10:28 ` [PATCH v18 4/9] mm: hugetlb: alloc " Muchun Song
2021-03-10 14:21 ` Oscar Salvador
2021-03-11 4:13 ` [External] " Muchun Song
2021-03-10 15:19 ` Michal Hocko
2021-03-10 18:56 ` Mike Kravetz
2021-03-10 21:11 ` Michal Hocko
2021-03-10 21:49 ` Paul E. McKenney
2021-03-10 22:10 ` Mike Kravetz
2021-03-10 23:28 ` Paul E. McKenney
2021-03-11 8:40 ` Michal Hocko
2021-03-11 12:17 ` Michal Hocko
2021-03-11 17:59 ` Mike Kravetz
2021-03-11 22:53 ` Mike Kravetz
2021-03-12 8:15 ` Michal Hocko
2021-03-12 17:50 ` Mike Kravetz
2021-03-11 4:26 ` [External] " Muchun Song
2021-03-11 8:46 ` Michal Hocko
2021-03-11 8:49 ` Muchun Song
2021-03-08 10:28 ` [PATCH v18 5/9] mm: hugetlb: set the PageHWPoison to the raw error page Muchun Song
2021-03-10 15:27 ` Michal Hocko
2021-03-11 6:34 ` [External] " Muchun Song
2021-03-11 8:50 ` Michal Hocko
2021-03-11 9:13 ` Muchun Song
2021-03-08 10:28 ` [PATCH v18 6/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-03-10 15:37 ` Michal Hocko
2021-03-10 17:15 ` Randy Dunlap
2021-03-11 6:36 ` [External] " Muchun Song
2021-03-11 6:36 ` Muchun Song
2021-03-08 10:28 ` [PATCH v18 7/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2021-03-08 10:28 ` [PATCH v18 8/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-03-10 15:39 ` Michal Hocko
2021-03-08 10:28 ` [PATCH v18 9/9] mm: hugetlb: optimize the code with the help of the compiler Muchun Song
2021-03-10 15:41 ` Michal Hocko
2021-03-11 7:33 ` Muchun Song [this message]
2021-03-11 8:55 ` [External] " Michal Hocko
2021-03-11 9:08 ` Muchun Song
2021-03-11 9:39 ` Michal Hocko
2021-03-11 10:00 ` Muchun Song
2021-03-11 12:16 ` Michal Hocko
2021-03-11 13:00 ` Muchun Song
2021-03-11 13:45 ` Oscar Salvador
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