From: Robert Richter <robert.richter@cavium.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Hanjun Guo <hanjun.guo@linaro.org>,
Yisheng Xie <xieyisheng1@huawei.com>,
James Morse <james.morse@arm.com>
Subject: Re: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA
Date: Thu, 5 Jan 2017 13:22:00 +0100 [thread overview]
Message-ID: <20170105122200.GV4930@rric.localdomain> (raw)
In-Reply-To: <20170105120819.GH679@arm.com>
On 05.01.17 12:08:20, Will Deacon wrote:
> On Thu, Jan 05, 2017 at 12:24:07PM +0100, Robert Richter wrote:
> > On 04.01.17 14:02:23, Will Deacon wrote:
> > > Using early_pfn_valid feels like a bodge to me, since having pfn_valid
> > > return false for something that early_pfn_valid says is valid (and is
> > > therefore initialised in the memmap) makes the NOMAP semantics even more
> > > confusing.
> >
> > The concern I have had with HOLES_IN_ZONE is that it enables
> > pfn_valid_within() for arm64. This means that each pfn of a section is
> > checked which is done only once for the section otherwise. With up to
> > 2^18 pages per section we traverse the memblock list by that factor
> > more often. There could be a performance regression.
>
> There could be, but we're trying to fix a bug here. I wouldn't have
> thought that walking over pfns like that is done very often.
The bug happens on a small number of machines depending on the memory
layout. The fix affects all systems. And right know the impact is
unclear.
> > I haven't numbers yet, since the fix causes another kernel crash. And,
> > this is the next problem I have. The crash doesn't happen otherwise. So,
> > either it uncovers another bug or the fix is incomplete. Though the
> > changes look like it should work. This needs more investigation.
>
> I really can't see how the fix causes a crash, and I couldn't reproduce
> it on any of my boards, nor could any of the Linaro folk afaik. Are you
> definitely running mainline with just these two patches from Ard?
Yes, just both patches applied. Various other solutions were working.
-Robert
next prev parent reply other threads:[~2017-01-05 12:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-14 9:11 [PATCH 0/2] arm64: numa: fix spurious BUG() on NOMAP regions Ard Biesheuvel
2016-12-14 9:11 ` [PATCH 1/2] mm: don't dereference struct page fields of invalid pages Ard Biesheuvel
2017-01-04 12:16 ` Will Deacon
2016-12-14 9:11 ` [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA Ard Biesheuvel
2016-12-15 15:39 ` Robert Richter
2016-12-15 16:07 ` Ard Biesheuvel
2016-12-16 17:10 ` Robert Richter
2016-12-16 1:57 ` Hanjun Guo
2016-12-16 17:14 ` Robert Richter
2017-01-04 13:28 ` Will Deacon
2017-01-04 13:50 ` Ard Biesheuvel
2017-01-04 14:02 ` Will Deacon
2017-01-05 11:24 ` Robert Richter
2017-01-05 12:08 ` Will Deacon
2017-01-05 12:22 ` Robert Richter [this message]
2017-01-05 19:49 ` Robert Richter
2017-01-06 12:03 ` Will Deacon
2017-01-06 12:22 ` Ard Biesheuvel
2017-02-06 13:36 ` Robert Richter
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