From: Muchun Song <songmuchun@bytedance.com>
To: Barry Song <21cnbao@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Oscar Salvador <osalvador@suse.de>,
Michal Hocko <mhocko@suse.com>,
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>,
Matthew Wilcox <willy@infradead.org>,
Xiongchun duan <duanxiongchun@bytedance.com>,
fam.zheng@bytedance.com, Muchun Song <smuchun@gmail.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH RESEND v2 4/4] selftests: vm: add a hugetlb test case
Date: Tue, 21 Sep 2021 21:18:43 +0800 [thread overview]
Message-ID: <CAMZfGtVHriw5jXGJDOCr2pxHmB5SPVPto8yWkZBDmjSw8dcVEQ@mail.gmail.com> (raw)
In-Reply-To: <CAGsJ_4zDKVkXf60d4ZPZjFJBN5L8wR1_57D_EUEzGZWcYhxn=A@mail.gmail.com>
On Tue, Sep 21, 2021 at 8:29 PM Barry Song <21cnbao@gmail.com> wrote:
>
> On Tue, Sep 21, 2021 at 2:26 AM Muchun Song <songmuchun@bytedance.com> wrote:
> >
> > On Sat, Sep 18, 2021 at 1:20 PM Barry Song <21cnbao@gmail.com> wrote:
> > >
> > > On Sat, Sep 18, 2021 at 12:08 AM Muchun Song <songmuchun@bytedance.com> wrote:
> > > >
> > > > Since the head vmemmap page frame associated with each HugeTLB page is
> > > > reused, we should hide the PG_head flag of tail struct page from the
> > > > user. Add a tese case to check whether it is work properly.
> > > >
> > >
> > > TBH, I am a bit confused. I was thinking about some kernel unit tests to make
> > > sure those kernel APIs touched by this patchset are still working as before.
> > > This userspace test, while certainly useful for checking the content of page
> > > frames as expected, doesn't directly prove things haven't changed.
> > >
> > > In patch 1/4, a couple of APIs have the fixup for the fake head issue.
> > > Do you think a test like the below would be more sensible?
> > > 1. alloc 2MB hugeTLB
> >
> > It is done in main().
> >
> > > 2. get each page frame
> > > 3. apply those APIs in each page frame
> > > 4. Those APIs work completely the same as before.
> >
> > Reading the flags of a page by /proc/kpageflags is done
> > in stable_page_flags(), which has invoked PageHead(),
> > PageTail(), PageCompound() and compound_head().
> > If those APIs work properly, the head page must have
> > 15 and 17 bits set. And tail pages must have 16 and 17
> > bits set but 15 unset.
> >
> > So I think check_page_flags() has done the step 2 to 4.
> > What do you think?
>
> yes. Thanks for your explanation. thereby, I think we just need some doc
> here to explain what it is checking. something like
> /*
> * pages other than the first page must be tail and shouldn't be head;
> * this also verifies kernel has correctly set the fake page_head to tail
> * while hugetlb_free_vmemmap is enabled
> */
Got it. Will do. Thanks.
> + for (i = 1; i < MAP_LENGTH / PAGE_SIZE; i++) {
> + read(fd, &pageflags, sizeof(pageflags));
> + if ((pageflags & TAIL_PAGE_FLAGS) != TAIL_PAGE_FLAGS ||
> + (pageflags & HEAD_PAGE_FLAGS) == HEAD_PAGE_FLAGS) {
> + close(fd);
> + printf("Tail page flags (%lx) is invalid\n", pageflags);
> + return -1;
> + }
> + }
> >
> > Thanks.
>
> Thanks
> barry
prev parent reply other threads:[~2021-09-21 13:19 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-17 3:48 [PATCH RESEND v2 0/4] Free the 2nd vmemmap page associated with each HugeTLB page Muchun Song
2021-09-17 3:48 ` [PATCH RESEND v2 1/4] mm: hugetlb: free " Muchun Song
2021-09-18 4:38 ` Barry Song
2021-09-18 10:06 ` Muchun Song
2021-09-21 6:43 ` Muchun Song
2021-09-21 10:22 ` Muchun Song
2021-09-21 0:11 ` Barry Song
2021-09-21 13:46 ` Muchun Song
2021-09-21 20:43 ` Barry Song
2021-09-22 2:38 ` Muchun Song
2021-09-22 7:36 ` Barry Song
2021-09-17 3:48 ` [PATCH RESEND v2 2/4] mm: hugetlb: replace hugetlb_free_vmemmap_enabled with a static_key Muchun Song
2021-09-18 4:55 ` Barry Song
2021-09-18 10:30 ` Muchun Song
2021-09-18 11:14 ` Barry Song
2021-09-18 11:47 ` Muchun Song
2021-09-18 12:27 ` Barry Song
2021-09-17 3:48 ` [PATCH RESEND v2 3/4] mm: sparsemem: use page table lock to protect kernel pmd operations Muchun Song
2021-09-18 5:06 ` Barry Song
2021-09-18 10:51 ` Muchun Song
2021-09-18 11:01 ` Barry Song
2021-09-17 3:48 ` [PATCH RESEND v2 4/4] selftests: vm: add a hugetlb test case Muchun Song
2021-09-18 5:20 ` Barry Song
2021-09-20 14:26 ` Muchun Song
2021-09-21 0:28 ` Barry Song
2021-09-21 13:18 ` Muchun Song [this message]
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