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From: Peter Zijlstra <peterz@infradead.org>
To: Mike Rapoport <rppt@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	David Hildenbrand <david@redhat.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>,
	Idan Yaniv <idan.yaniv@ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	linux-arch@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
	linux-nvdimm@lists.01.org, Shuah Khan <shuah@kernel.org>,
	x86@kernel.org, Matthew Wilcox <willy@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	James Bottomley <jejb@linux.ibm.com>,
	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>,
	Dan Williams <dan.j.williams@intel.com>,
	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: Tue, 29 Sep 2020 17:15:52 +0200
Message-ID: <20200929151552.GS2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200929145813.GA3226834@linux.ibm.com>

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.

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  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 [this message]
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
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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