From: Will Deacon <will.deacon@arm.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: James Morse <james.morse@arm.com>,
Michal Hocko <mhocko@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
Pavel Tatashin <Pavel.Tatashin@microsoft.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: A crash on ARM64 in move_freepages_block due to uninitialized pages in reserved memory
Date: Thu, 30 Aug 2018 17:11:37 +0100 [thread overview]
Message-ID: <20180830161137.GC13005@arm.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1808301148260.18300@file01.intranet.prod.int.rdu2.redhat.com>
On Thu, Aug 30, 2018 at 11:58:19AM -0400, Mikulas Patocka wrote:
> On Wed, 29 Aug 2018, James Morse wrote:
> > HOLES_IN_ZONE is similar, if some memory is smaller than MAX_ORDER_NR_PAGES,
> > possibly due to nomap holes.
> >
> > 6d526ee26ccd only enabled it for NUMA systems on arm64, because the NUMA code
> > was first to fall foul of this, but there is nothing NUMA specific about nomap
> > holes within a MAX_ORDER_NR_PAGES region.
> >
> > I'm convinced arm64 should always enable HOLES_IN_ZONE because nomap pages can
> > occur anywhere. I'll post a fix.
>
> But x86 had the same bug -
> https://bugzilla.redhat.com/show_bug.cgi?id=1598462
Yeah, that's not readable and lkml.org is down. Any idea what x86 did?
> And x86 fixed it without enabling HOLES_IN_ZONE. On x86, the BIOS can also
> reserve any memory range - so you can have arbitrary holes there that are
> not predictable when the kernel is compiled.
What happens when the BIOS reserves a page on x86? Is it still mapped by
the kernel (and therefore has a valid struct page) or is it treated like
NOMAP?
> Currently HOLES_IN_ZONE is selected only for ia64, mips/octeon - so does
> it mean that all the other architectures don't have holes in the memory
> map?
Possibly. Note also that arm64 already selects HOLES_IN_ZONE if NUMA.
> What should be architecture-independent way how to handle the holes?
Until firmware is architecture-independent, I think handling this
generically is a lost cause.
Will
next prev parent reply other threads:[~2018-08-30 16:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-17 19:44 Mikulas Patocka
2018-08-21 10:44 ` Michal Hocko
2018-08-21 12:58 ` James Morse
2018-08-23 11:02 ` Mikulas Patocka
2018-08-23 11:10 ` Michal Hocko
2018-08-23 11:16 ` Mikulas Patocka
2018-08-23 11:23 ` Michal Hocko
2018-08-23 13:13 ` Pasha Tatashin
2018-08-23 13:14 ` Pasha Tatashin
2018-08-23 14:34 ` Mikulas Patocka
2018-08-23 14:06 ` James Morse
2018-08-24 11:41 ` Michal Hocko
2018-08-29 17:37 ` James Morse
2018-08-30 15:58 ` Mikulas Patocka
2018-08-30 16:11 ` Will Deacon [this message]
2018-08-30 16:25 ` James Morse
2018-09-03 19:33 ` Michal Hocko
2018-09-07 17:47 ` James Morse
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