From: Michael Ellerman <mpe@ellerman.id.au>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Florian Weimer <fweimer@redhat.com>,
linux-arch@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
linuxppc-dev@lists.ozlabs.org,
Thomas Gleixner <tglx@linutronix.de>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: POWER: Unexpected fault when writing to brk-allocated memory
Date: Wed, 08 Nov 2017 15:56:06 +1100 [thread overview]
Message-ID: <87y3nh2wt5.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <2ce0a91c-985c-aad8-abfa-e91bc088bb3e@linux.vnet.ibm.com>
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:
>>
>> If it is decided to keep these kind of heuristics, can we get just a
>> small but reasonably precise description of each change to the
>> interface and ways for using the new functionality, such that would be
>> suitable for the man page? I couldn't fix powerpc because nothing
>> matches and even Aneesh and you differ on some details (MAP_FIXED
>> behaviour).
>
>
> I would consider MAP_FIXED as my mistake. We never discussed this
> explicitly and I kind of assumed it to behave the same way. ie, we
> search in lower address space (128TB) if the hint addr is below 128TB.
>
> IIUC we agree on the below.
>
> 1) MAP_FIXED allow the addr to be used, even if hint addr is below 128TB
> but hint_addr + len is > 128TB.
So:
mmap(0x7ffffffff000, 0x2000, ..., MAP_FIXED ...) = 0x7ffffffff000
> 2) For everything else we search in < 128TB space if hint addr is below
> 128TB
mmap((x < 128T), 0x1000, ...) = (y < 128T)
...
mmap(0x7ffffffff000, 0x1000, ...) = 0x7ffffffff000
mmap(0x800000000000, 0x1000, ...) = 0x800000000000
...
mmap((x >= 128T), 0x1000, ...) = (y >= 128T)
> 3) We don't switch to large address space if hint_addr + len > 128TB.
> The decision to switch to large address space is primarily based on hint
> addr
But does the mmap succeed in that case or not?
ie: mmap(0x7ffffffff000, 0x2000, ...) = ?
cheers
next prev parent reply other threads:[~2017-11-08 4:56 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <f251fc3e-c657-ebe8-acc8-f55ab4caa667@redhat.com>
[not found] ` <20171105231850.5e313e46@roar.ozlabs.ibm.com>
[not found] ` <871slcszfl.fsf@linux.vnet.ibm.com>
[not found] ` <20171106174707.19f6c495@roar.ozlabs.ibm.com>
[not found] ` <24b93038-76f7-33df-d02e-facb0ce61cd2@redhat.com>
[not found] ` <20171106192524.12ea3187@roar.ozlabs.ibm.com>
[not found] ` <d52581f4-8ca4-5421-0862-3098031e29a8@linux.vnet.ibm.com>
[not found] ` <546d4155-5b7c-6dba-b642-29c103e336bc@redhat.com>
2017-11-07 5:07 ` POWER: Unexpected fault when writing to brk-allocated memory Nicholas Piggin
2017-11-07 8:15 ` Florian Weimer
2017-11-07 9:24 ` Nicholas Piggin
2017-11-07 11:16 ` Kirill A. Shutemov
2017-11-07 11:15 ` Kirill A. Shutemov
2017-11-07 11:26 ` Florian Weimer
2017-11-07 11:44 ` Kirill A. Shutemov
2017-11-07 13:05 ` Florian Weimer
2017-11-07 13:16 ` Kirill A. Shutemov
2017-11-08 6:08 ` Michael Ellerman
2017-11-08 6:18 ` Florian Weimer
2017-11-07 11:56 ` Nicholas Piggin
2017-11-07 12:28 ` Kirill A. Shutemov
2017-11-07 13:33 ` Nicholas Piggin
2017-11-07 13:45 ` Aneesh Kumar K.V
2017-11-07 14:01 ` Kirill A. Shutemov
2017-11-09 17:15 ` Nicholas Piggin
2017-11-09 19:44 ` Matthew Wilcox
2017-11-10 1:26 ` Nicholas Piggin
[not found] ` <063D6719AE5E284EB5DD2968C1650D6DD00B84EF@AcuExch.aculab.com>
2017-11-11 10:30 ` Nicholas Piggin
2017-11-08 4:56 ` Michael Ellerman [this message]
2017-11-08 8:30 ` Kirill A. Shutemov
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