From: Dave Hansen <dave.hansen@intel.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
"peterz@infradead.org" <peterz@infradead.org>
Cc: "adobriyan@gmail.com" <adobriyan@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"rppt@kernel.org" <rppt@kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"jejb@linux.ibm.com" <jejb@linux.ibm.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"mingo@redhat.com" <mingo@redhat.com>,
"luto@kernel.org" <luto@kernel.org>,
"kirill@shutemov.name" <kirill@shutemov.name>,
"bp@alien8.de" <bp@alien8.de>,
"rppt@linux.ibm.com" <rppt@linux.ibm.com>,
"arnd@arndb.de" <arnd@arndb.de>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings
Date: Wed, 30 Oct 2019 10:58:49 -0700 [thread overview]
Message-ID: <775eb0cf-7189-a314-5dde-f720b56ec3b2@intel.com> (raw)
In-Reply-To: <b4d87f54b02cfccb58442f791485cad1ac080063.camel@intel.com>
On 10/30/19 10:48 AM, Edgecombe, Rick P wrote:
> On Wed, 2019-10-30 at 11:04 +0100, Peter Zijlstra wrote:
>>> You mean shatter performance?
>>
>> Shatter (all) large pages.
>
> So it looks like this is already happening then to some degree. It's not just
> BPF either, any module_alloc() user is going to do something similar with the
> direct map alias of the page they got for the text.
>
> So there must be at least some usages where breaking the direct map down, for
> like a page to store a key or something, isn't totally horrible.
The systems that really need large pages are the large ones. They have
the same TLBs and data structures as really little systems, but orders
of magnitude more address space. Modules and BPF are a (hopefully) drop
in the bucket on small systems and they're really inconsequential on
really big systems.
Modules also require privilege.
Allowing random user apps to fracture the direct map for every page of
their memory or *lots* of pages of their memory is an entirely different
kind of problem from modules. It takes a "drop in the bucket"
fracturing and turns it into the common case.
next prev parent reply other threads:[~2019-10-30 17:58 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-27 10:17 [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Mike Rapoport
2019-10-27 10:17 ` Mike Rapoport
2019-10-28 12:31 ` Kirill A. Shutemov
2019-10-28 13:00 ` Mike Rapoport
2019-10-28 13:16 ` Kirill A. Shutemov
2019-10-28 13:55 ` Peter Zijlstra
2019-10-28 19:59 ` Edgecombe, Rick P
2019-10-28 21:00 ` Peter Zijlstra
2019-10-29 17:27 ` Edgecombe, Rick P
2019-10-30 10:04 ` Peter Zijlstra
2019-10-30 15:35 ` Alexei Starovoitov
2019-10-30 18:39 ` Peter Zijlstra
2019-10-30 18:52 ` Alexei Starovoitov
2019-10-30 17:48 ` Edgecombe, Rick P
2019-10-30 17:58 ` Dave Hansen [this message]
2019-10-30 18:01 ` Dave Hansen
2019-10-29 5:43 ` Dan Williams
2019-10-29 6:43 ` Kirill A. Shutemov
2019-10-29 8:56 ` Peter Zijlstra
2019-10-29 11:00 ` Kirill A. Shutemov
2019-10-29 12:39 ` AMD TLB errata, (Was: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings) Peter Zijlstra
2019-11-15 14:12 ` Tom Lendacky
2019-11-15 14:31 ` Peter Zijlstra
2019-10-29 19:43 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Dan Williams
2019-10-29 20:07 ` Dave Hansen
2019-10-29 7:08 ` Christopher Lameter
2019-10-29 8:55 ` Mike Rapoport
2019-10-29 10:12 ` Christopher Lameter
2019-10-30 7:11 ` Mike Rapoport
2019-10-30 12:09 ` Christopher Lameter
2019-10-28 14:55 ` David Hildenbrand
2019-10-28 17:12 ` Dave Hansen
2019-10-28 17:32 ` Sean Christopherson
2019-10-28 18:08 ` Matthew Wilcox
2019-10-29 9:28 ` Mike Rapoport
2019-10-29 9:19 ` Mike Rapoport
2019-10-28 18:02 ` Andy Lutomirski
2019-10-29 11:02 ` David Hildenbrand
2019-10-30 8:15 ` Mike Rapoport
2019-10-30 8:19 ` David Hildenbrand
2019-10-31 19:16 ` Mike Rapoport
2019-10-31 21:52 ` Dan Williams
2019-10-27 10:30 ` Florian Weimer
2019-10-27 11:00 ` Mike Rapoport
2019-10-28 20:23 ` Florian Weimer
2019-10-29 9:01 ` Mike Rapoport
2019-10-28 20:44 ` Andy Lutomirski
2019-10-29 9:32 ` Mike Rapoport
2019-10-29 17:00 ` Andy Lutomirski
2019-10-30 8:40 ` Mike Rapoport
2019-10-30 21:28 ` Andy Lutomirski
2019-10-31 7:21 ` Mike Rapoport
2019-12-05 15:34 ` Mike Rapoport
2019-12-08 14:10 ` [PATCH] mm: extend memfd with ability to create secret memory kbuild test robot
2019-10-29 11:25 ` [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Reshetova, Elena
2019-10-29 15:13 ` Tycho Andersen
2019-10-29 17:03 ` Andy Lutomirski
2019-10-29 17:37 ` Alan Cox
2019-10-29 17:43 ` James Bottomley
2019-10-29 18:10 ` Andy Lutomirski
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