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From: Muchun Song <songmuchun@bytedance.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <osalvador@suse.de>,
	Michal Hocko <mhocko@suse.com>,
	"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	David Hildenbrand <david@redhat.com>,
	Chen Huang <chenhuang5@huawei.com>,
	"Bodeddula, Balasubramaniam" <bodeddub@amazon.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Xiongchun duan <duanxiongchun@bytedance.com>,
	fam.zheng@bytedance.com, linux-doc@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Qi Zheng <zhengqi.arch@bytedance.com>
Subject: Re: [PATCH 2/5] mm: introduce save_page_flags to cooperate with show_page_flags
Date: Tue, 27 Jul 2021 15:06:28 +0800	[thread overview]
Message-ID: <CAMZfGtUaSsfjf4HSCsHMHFNxVaGrTXjVqE5iExM8JkMJPx169g@mail.gmail.com> (raw)
In-Reply-To: <fea1d845-209a-e2d5-6fcc-dbf17c949861@oracle.com>

On Tue, Jul 27, 2021 at 7:18 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 7/14/21 2:17 AM, Muchun Song wrote:
> > Introduce save_page_flags to return the page flags which can cooperate
> > with show_page_flags. If we want to hihe some page flags from users, it
> > will be useful to alter save_page_flags directly. This is a preparation
> > for the next patch to hide some page flags from users.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  include/trace/events/mmflags.h  | 3 +++
> >  include/trace/events/page_ref.h | 8 ++++----
> >  2 files changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> > index 390270e00a1d..69cb84b1257e 100644
> > --- a/include/trace/events/mmflags.h
> > +++ b/include/trace/events/mmflags.h
> > @@ -121,6 +121,9 @@ IF_HAVE_PG_IDLE(PG_idle,          "idle"          )               \
> >  IF_HAVE_PG_ARCH_2(PG_arch_2,         "arch_2"        )               \
> >  IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison")
> >
> > +#define save_page_flags(page)                                                \
> > +     (((page)->flags & ~PAGEFLAGS_MASK))
> > +
>
> Looking ahead to the next patch, this is changed to hide the PG_head
> flag for 'fake' head pages.
>
> IIRC, all vmemmap pages except the first will be mapped read only.  So,
> all vmemmap pages with 'fake' head pages will be read only.
>
> It seems that all the modified trace events below are associated with
> updates to page structs.  Therefore, it seems these events will never
> experience a 'fake' head page.  Am I missing something?

Totally right. I didn't realize this point before. We cannot see a fake page
struct in page refcount tracing. So this patch is definitely pointless. I'll
drop it in the next version. Thanks Mike.


>
> --
> Mike Kravetz

  reply	other threads:[~2021-07-27  7:07 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14  9:17 [PATCH 0/5] Free the 2nd vmemmap page associated with each HugeTLB page Muchun Song
2021-07-14  9:17 ` [PATCH 1/5] mm: introduce PAGEFLAGS_MASK to replace ((1UL << NR_PAGEFLAGS) - 1) Muchun Song
2021-07-26 21:04   ` Mike Kravetz
2021-07-27  6:27     ` Muchun Song
2021-07-29  6:00       ` Muchun Song
2021-07-14  9:17 ` [PATCH 2/5] mm: introduce save_page_flags to cooperate with show_page_flags Muchun Song
2021-07-26 23:18   ` Mike Kravetz
2021-07-27  7:06     ` Muchun Song [this message]
2021-07-14  9:17 ` [PATCH 3/5] mm: hugetlb: free the 2nd vmemmap page associated with each HugeTLB page Muchun Song
2021-07-26 21:16   ` Matthew Wilcox
2021-07-26 23:56     ` Mike Kravetz
2021-07-27  7:15     ` Muchun Song
2021-07-14  9:17 ` [PATCH 4/5] mm: hugetlb: replace hugetlb_free_vmemmap_enabled with a static_key Muchun Song
2021-07-14  9:18 ` [PATCH 5/5] mm: sparsemem: use page table lock to protect kernel pmd operations Muchun Song

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