From: David Hildenbrand <david@redhat.com>
To: jejb@linux.ibm.com, Mike Rapoport <rppt@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
linux-mm@kvack.org, Will Deacon <will@kernel.org>,
linux-kselftest@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Christopher Lameter <cl@linux.com>, Shuah Khan <shuah@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Elena Reshetova <elena.reshetova@intel.com>,
linux-arch@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
linux-nvdimm@lists.01.org, Idan Yaniv <idan.yaniv@ibm.com>,
x86@kernel.org, Matthew Wilcox <willy@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andy Lutomirski <luto@kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Thomas Gleixner <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
Palmer Dabbelt <palmer@dabbelt.com>,
linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>
Subject: Re: [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation
Date: Wed, 30 Sep 2020 16:45:11 +0200 [thread overview]
Message-ID: <6568383f-4e43-2fe4-ecf1-8a55e306440b@redhat.com> (raw)
In-Reply-To: <371c27d97067654171e5c1019340b56cffadae7a.camel@linux.ibm.com>
On 30.09.20 16:39, James Bottomley wrote:
> On Wed, 2020-09-30 at 13:27 +0300, Mike Rapoport wrote:
>> On Tue, Sep 29, 2020 at 05:15:52PM +0200, Peter Zijlstra wrote:
>>> On Tue, Sep 29, 2020 at 05:58:13PM +0300, Mike Rapoport wrote:
>>>> On Tue, Sep 29, 2020 at 04:12:16PM +0200, Peter Zijlstra wrote:
>>>>> It will drop them down to 4k pages. Given enough inodes, and
>>>>> allocating only a single sekrit page per pmd, we'll shatter the
>>>>> directmap into 4k.
>>>>
>>>> Why? Secretmem allocates PMD-size page per inode and uses it as a
>>>> pool of 4K pages for that inode. This way it ensures that
>>>> __kernel_map_pages() is always called on PMD boundaries.
>>>
>>> Oh, you unmap the 2m page upfront? I read it like you did the unmap
>>> at the sekrit page alloc, not the pool alloc side of things.
>>>
>>> Then yes, but then you're wasting gobs of memory. Basically you can
>>> pin 2M per inode while only accounting a single page.
>>
>> Right, quite like THP :)
>>
>> I considered using a global pool of 2M pages for secretmem and
>> handing 4K pages to each inode from that global pool. But I've
>> decided to waste memory in favor of simplicity.
>
> I can also add that the user space consumer of this we wrote does its
> user pool allocation at a 2M granularity, so nothing is actually
> wasted.
... for that specific user space consumer. (or am I missing something?)
--
Thanks,
David / dhildenb
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next prev parent reply other threads:[~2020-09-30 14:45 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 13:28 [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-24 13:28 ` [PATCH v6 1/6] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 2/6] mmap: make mlock_future_check() global Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-29 4:58 ` Edgecombe, Rick P
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 20:06 ` Edgecombe, Rick P
2020-09-30 10:35 ` Mike Rapoport
2020-09-30 20:11 ` Edgecombe, Rick P
2020-10-11 9:42 ` Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 4/6] arch, mm: wire up memfd_secret system call were relevant Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-09-25 7:41 ` Peter Zijlstra
2020-09-25 9:00 ` David Hildenbrand
2020-09-25 9:50 ` Peter Zijlstra
2020-09-25 10:31 ` Mark Rutland
2020-09-25 14:57 ` Tycho Andersen
2020-09-29 14:04 ` Mike Rapoport
2020-09-29 13:07 ` Mike Rapoport
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 13:05 ` Mike Rapoport
2020-09-29 14:12 ` Peter Zijlstra
2020-09-29 14:31 ` Dave Hansen
2020-09-29 14:58 ` Mike Rapoport
2020-09-29 15:15 ` Peter Zijlstra
2020-09-30 10:27 ` Mike Rapoport
2020-09-30 14:39 ` James Bottomley
2020-09-30 14:45 ` David Hildenbrand [this message]
2020-09-30 15:17 ` James Bottomley
2020-09-30 15:25 ` David Hildenbrand
2020-09-30 15:09 ` Matthew Wilcox
2020-10-01 8:14 ` Mike Rapoport
2020-09-29 15:03 ` James Bottomley
2020-09-30 10:20 ` Mike Rapoport
2020-09-30 10:43 ` Peter Zijlstra
2020-09-24 13:29 ` [PATCH v6 6/6] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2020-09-24 13:35 ` [PATCH] man2: new page describing memfd_secret() system call Mike Rapoport
2020-09-24 14:55 ` Alejandro Colomar
2020-10-03 9:32 ` Alejandro Colomar
2020-10-05 7:32 ` Mike Rapoport
2020-11-16 21:01 ` [PATCH v2] memfd_secret.2: New " Alejandro Colomar
2020-11-17 6:26 ` Mike Rapoport
2020-09-25 2:34 ` [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton
2020-09-25 6:42 ` Mike Rapoport
2020-11-01 11:09 ` Hagen Paul Pfeifer
2020-11-02 15:40 ` Mike Rapoport
2020-11-03 13:52 ` Hagen Paul Pfeifer
2020-11-03 16:30 ` Mike Rapoport
2020-11-04 11:39 ` Hagen Paul Pfeifer
2020-11-04 17:02 ` Mike Rapoport
2020-11-09 10:41 ` Hagen Paul Pfeifer
2020-11-02 9:11 ` David Hildenbrand
2020-11-02 9:31 ` David Hildenbrand
2020-11-02 17:43 ` Mike Rapoport
2020-11-02 17:51 ` David Hildenbrand
2020-11-03 9:52 ` Mike Rapoport
2020-11-03 10:11 ` David Hildenbrand
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