Linux-RISC-V Archive on lore.kernel.org
 help / color / Atom feed
From: James Bottomley <jejb@linux.ibm.com>
To: David Hildenbrand <david@redhat.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 08:17:11 -0700
Message-ID: <ba7fbd31b37363c002318f633d7cc47d9ef46822.camel@linux.ibm.com> (raw)
In-Reply-To: <6568383f-4e43-2fe4-ecf1-8a55e306440b@redhat.com>

On Wed, 2020-09-30 at 16:45 +0200, David Hildenbrand wrote:
> 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?)

I'm not sure I understand what you mean?  It's designed to be either
the standard wrapper or an example of how to do the standard wrapper
for the syscall.  It uses the same allocator system glibc uses for
malloc/free ... which pretty much everyone uses instead of calling
sys_brk directly.  If you look at the granularity glibc uses for
sys_brk, it's not 4k either.

James



_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply index

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
2020-09-30 15:17                   ` James Bottomley [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ba7fbd31b37363c002318f633d7cc47d9ef46822.camel@linux.ibm.com \
    --to=jejb@linux.ibm.com \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=catalin.marinas@arm.com \
    --cc=cl@linux.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=david@redhat.com \
    --cc=elena.reshetova@intel.com \
    --cc=hpa@zytor.com \
    --cc=idan.yaniv@ibm.com \
    --cc=kirill@shutemov.name \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=luto@kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mingo@redhat.com \
    --cc=mtk.manpages@gmail.com \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --cc=peterz@infradead.org \
    --cc=rppt@kernel.org \
    --cc=rppt@linux.ibm.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=tycho@tycho.ws \
    --cc=viro@zeniv.linux.org.uk \
    --cc=will@kernel.org \
    --cc=willy@infradead.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-RISC-V Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-riscv/0 linux-riscv/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-riscv linux-riscv/ https://lore.kernel.org/linux-riscv \
		linux-riscv@lists.infradead.org
	public-inbox-index linux-riscv

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-riscv


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git