From: Will Deacon <will.deacon@arm.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>,
jmorris@namei.org, sashal@kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-nvdimm@lists.01.org, akpm@linux-foundation.org,
dave.hansen@linux.intel.com, dan.j.williams@intel.com,
keith.busch@intel.com, vishal.l.verma@intel.com,
dave.jiang@intel.com, zwisler@kernel.org,
thomas.lendacky@amd.com, ying.huang@intel.com,
fengguang.wu@intel.com, bp@suse.de, bhelgaas@google.com,
baiyaowei@cmss.chinamobile.com, tiwai@suse.de,
jglisse@redhat.com, catalin.marinas@arm.com,
rppt@linux.vnet.ibm.com, ard.biesheuvel@linaro.org,
andrew.murray@arm.com, james.morse@arm.com, marc.zyngier@arm.com,
sboyd@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: configurable sparsemem section size
Date: Thu, 25 Apr 2019 16:31:38 +0100 [thread overview]
Message-ID: <20190425153138.GC25193@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <20190425152550.GY12751@dhcp22.suse.cz>
On Thu, Apr 25, 2019 at 05:25:50PM +0200, Michal Hocko wrote:
> On Tue 23-04-19 16:38:43, Pavel Tatashin wrote:
> > sparsemem section size determines the maximum size and alignment that
> > is allowed to offline/online memory block. The bigger the size the less
> > the clutter in /sys/devices/system/memory/*. On the other hand, however,
> > there is less flexability in what granules of memory can be added and
> > removed.
> >
> > Recently, it was enabled in Linux to hotadd persistent memory that
> > can be either real NV device, or reserved from regular System RAM
> > and has identity of devdax.
> >
> > The problem is that because ARM64's section size is 1G, and devdax must
> > have 2M label section, the first 1G is always missed when device is
> > attached, because it is not 1G aligned.
> >
> > Allow, better flexibility by making section size configurable.
>
> Is there any inherent reason (64k page size?) that enforces such a large
> memsection?
I gave *vague* memories of running out of bits in the page flags if we
changed this, but that was a while back. If that's no longer the case,
then I'm open to changing the value, but I really don't want to expose
it as a Kconfig option as proposed in this patch. People won't have a
clue what to set and it doesn't help at all with the single-Image effort.
Will
next prev parent reply other threads:[~2019-04-25 15:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-23 20:38 [PATCH] arm64: configurable sparsemem section size Pavel Tatashin
2019-04-24 9:07 ` Anshuman Khandual
2019-04-24 19:48 ` Pavel Tatashin
2019-04-24 19:54 ` Pavel Tatashin
2019-04-24 20:24 ` Dan Williams
2019-04-24 20:33 ` Pavel Tatashin
2019-04-25 3:06 ` Anshuman Khandual
2019-04-25 15:25 ` Michal Hocko
2019-04-25 15:31 ` Will Deacon [this message]
2019-04-25 15:41 ` Michal Hocko
2019-04-25 17:57 ` Pavel Tatashin
2019-04-26 5:33 ` Michal Hocko
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