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Mon, 20 Sep 2021 07:26:40 -0700 (PDT) MIME-Version: 1.0 References: <20210917034815.80264-1-songmuchun@bytedance.com> <20210917034815.80264-5-songmuchun@bytedance.com> In-Reply-To: From: Muchun Song Date: Mon, 20 Sep 2021 22:26:01 +0800 Message-ID: Subject: Re: [PATCH RESEND v2 4/4] selftests: vm: add a hugetlb test case To: Barry Song <21cnbao@gmail.com> Cc: Mike Kravetz , Andrew Morton , Oscar Salvador , Michal Hocko , Barry Song , David Hildenbrand , Chen Huang , "Bodeddula, Balasubramaniam" , Jonathan Corbet , Matthew Wilcox , Xiongchun duan , fam.zheng@bytedance.com, Muchun Song , Qi Zheng , linux-doc@vger.kernel.org, LKML , Linux-MM Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D457CF0000B1 X-Stat-Signature: 35r7a6dxkpq6dg7i6mz8mia59zidr5en Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=wmQ7DtwN; spf=pass (imf16.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.215.176 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com; dmarc=pass (policy=none) header.from=bytedance.com X-HE-Tag: 1632148001-463100 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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? Thanks.