Re: [PATCH v4 07/14] device-dax: compound devmap support

From: Joao Martins <joao.m.martins@oracle.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Linux MM <linux-mm@kvack.org>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Matthew Wilcox <willy@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	John Hubbard <jhubbard@nvidia.com>,
	Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>, Christoph Hellwig <hch@lst.de>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v4 07/14] device-dax: compound devmap support
Date: Fri, 5 Nov 2021 14:10:03 +0000	[thread overview]
Message-ID: <bfc9f754-e927-f6fa-7da8-2811fe5c8808@oracle.com> (raw)
In-Reply-To: <CAPcyv4jqdPaLPOydb_GWvVP4d+hRkcu7CnP_Ud-CQXHcqTLWKw@mail.gmail.com>

On 11/5/21 00:38, Dan Williams wrote:
> On Fri, Aug 27, 2021 at 7:59 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> Use the newly added compound devmap facility which maps the assigned dax
>> ranges as compound pages at a page size of @align. Currently, this means,
>> that region/namespace bootstrap would take considerably less, given that
>> you would initialize considerably less pages.
>>
>> On setups with 128G NVDIMMs the initialization with DRAM stored struct
>> pages improves from ~268-358 ms to ~78-100 ms with 2M pages, and to less
>> than a 1msec with 1G pages.
>>
>> dax devices are created with a fixed @align (huge page size) which is
>> enforced through as well at mmap() of the device. Faults, consequently
>> happen too at the specified @align specified at the creation, and those
>> don't change through out dax device lifetime.
> 
> s/through out/throughout/
> 
>> MCEs poisons a whole dax huge page, as well as splits occurring at the configured page size.
> 
> A clarification here, MCEs trigger memory_failure() to *unmap* a whole
> dax huge page, the poison stays limited to a single cacheline.
> 
Ah, yes. I'll fix it for v5.

> Otherwise the patch looks good to me.
> 
Thanks!

Btw, does 'looks good' == Reviewed-by (with the commit message clarification above) or is
it that 'should be good with the ammend above and you get the tag in the next round' ?

Asking as IIRC you mentioned this too some other time(s) (in the simpler sparse-vmemmap
patches) hence just clarifying to understand your expected 'process' better.

Also, I will be splitting this series as mentioned in the other discussion ...

https://lore.kernel.org/linux-mm/20211019160136.GH3686969@ziepe.ca/

... So this patch and the previous one should be the last two patches of the series
and the rest (gup, sparse-vmemmmap) will go in parallel.