Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 15 Mar 2021 15:07:48 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Zi Yan <ziy@nvidia.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Sandipan Das <sandipan@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Yang Shi <shy828301@gmail.com>,
        Mika Penttila <mika.penttila@nextfour.com>
Subject: Re: [PATCH v3] mm: huge_memory: a new debugfs interface for
 splitting THP tests.
Message-ID: <20210315120748.nuw5vk6grmfacact@box>
References: <20210312005712.116888-1-zi.yan@sent.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210312005712.116888-1-zi.yan@sent.com>
Precedence: bulk

On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> We do not have a direct user interface of splitting the compound page
> backing a THP

But we do. You expand it.

> and there is no need unless we want to expose the THP
> implementation details to users. Make <debugfs>/split_huge_pages accept
> a new command to do that.
> 
> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
> <debugfs>/split_huge_pages, THPs within the given virtual address range
> from the process with the given pid are split. It is used to test
> split_huge_page function. In addition, a selftest program is added to
> tools/testing/selftests/vm to utilize the interface by splitting
> PMD THPs and PTE-mapped THPs.
> 

Okay, makes sense.

But it doesn't cover non-mapped THPs. tmpfs may have file backed by THP
that mapped nowhere. Do we want to cover this case too?

Maybe have PID:<pid>,<vaddr_start>,<vaddr_end> and
FILE:<path>,<off_start>,<off_end> ?

-- 
 Kirill A. Shutemov