From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Sasha Levin <sashal@kernel.org>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Michal Hocko <mhocko@suse.com>,
Oscar Salvador <osalvador@suse.de>,
Vlastimil Babka <vbabka@suse.cz>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Jason Gunthorpe <jgg@ziepe.ca>, Marc Zyngier <maz@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Will Deacon <will.deacon@arm.com>,
James Morse <james.morse@arm.com>,
James Morris <jmorris@namei.org>
Subject: Re: dax alignment problem on arm64 (and other achitectures)
Date: Fri, 29 Jan 2021 14:12:25 -0500 [thread overview]
Message-ID: <CA+CK2bD7rXgs9UTX7QNNDAES0z32qV-gq+7TUwzx_zKHhrtUDw@mail.gmail.com> (raw)
In-Reply-To: <CA+CK2bBw1yMH2bAindymk-+yZRgAWncqybWhG5x3TJiX9-tSnQ@mail.gmail.com>
On Fri, Jan 29, 2021 at 2:06 PM Pavel Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> > > Definitely, but we should try figuring out what's going on here. I
> > > assume on x86-64 it behaves differently?
> >
> > Yes, we should root cause. I highly suspect that there is somewhere
> > alignment miscalculations happen that cause this memory waste with the
> > offset 16M. I am also not sure why the 2M label size was increased,
> > and why 16M is now an alignment requirement.
>
> This appears to be because even if we set vmemmap to be outside of the
> dax device, the alignment calculates the maximum size of vmemmap for
> this device, and subtracts it from the devdax size.
> See [1], line 795 is where this offset is calculated.
>
> This also explains why with 64K pages, the 16M offset worked: because
> fewer struct pages were able to fit within 16M - label size.
>
> [1] https://soleen.com/source/xref/linux/drivers/nvdimm/pfn_devs.c?r=b7b3c01b&mo=18459&fi=718#795
Actually, strike the previous e-mail. The extra space is when we
reserve vmemmap from devdax. IFF we do it from mem, the extra space is
not added. Now, this alignment makes total sense.
Pasha
next prev parent reply other threads:[~2021-01-29 19:13 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 20:43 dax alignment problem on arm64 (and other achitectures) Pavel Tatashin
2021-01-27 21:09 ` David Hildenbrand
2021-01-27 21:49 ` Pavel Tatashin
2021-01-27 22:18 ` David Hildenbrand
2021-01-27 23:33 ` Pavel Tatashin
2021-01-28 15:03 ` David Hildenbrand
2021-01-29 2:06 ` Pavel Tatashin
2021-01-29 13:19 ` David Hildenbrand
2021-01-29 16:24 ` Pavel Tatashin
2021-01-29 19:06 ` Pavel Tatashin
2021-01-29 19:12 ` Pavel Tatashin [this message]
2021-01-29 19:41 ` Pavel Tatashin
2021-01-29 2:55 ` Dan Williams
2021-01-29 13:50 ` Pavel Tatashin
2021-01-29 14:50 ` Joao Martins
2021-01-29 16:32 ` Pavel Tatashin
2021-01-29 17:22 ` Joao Martins
2021-01-29 20:26 ` Dan Williams
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