linux-kernel - Re: [PATCH v3] mm: huge_memory: a new debugfs interface for splitting THP tests.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210315120748.nuw5vk6grmfacact@box>
Date:   Mon, 15 Mar 2021 15:07:48 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Zi Yan <ziy@...dia.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        Mika Penttila <mika.penttila@...tfour.com>
Subject: Re: [PATCH v3] mm: huge_memory: a new debugfs interface for
 splitting THP tests.

On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.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