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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	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>,
	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>,
	nvdimm@lists.linux.dev, linux-doc@vger.kernel.org
Subject: Re: [PATCH v4 08/14] mm/gup: grab head page refcount once for group of subpages
Date: Tue, 28 Sep 2021 15:01:50 -0300	[thread overview]
Message-ID: <20210928180150.GI3544071@ziepe.ca> (raw)
In-Reply-To: <8c23586a-eb3b-11a6-e72a-dcc3faad4e96@oracle.com>

On Thu, Sep 23, 2021 at 05:51:04PM +0100, Joao Martins wrote:
> On 8/31/21 6:05 PM, Jason Gunthorpe wrote:

> >> Switching to similar iteration logic to unpin would look something like
> >> this (still untested):
> >>
> >>         for_each_compound_range(index, &page, npages, head, refs) {
> >>                 pgmap = get_dev_pagemap(pfn + *nr, pgmap);
> > 
> > I recall talking to DanW about this and we agreed it was unnecessary
> > here to hold the pgmap and should be deleted.
> 
> Yeap, I remember that conversation[0]. It was a long time ago, and I am
> not sure what progress was made there since the last posting? Dan, any
> thoughts there?
> 
> [0]
> https://lore.kernel.org/linux-mm/161604050866.1463742.7759521510383551055.stgit@dwillia2-desk3.amr.corp.intel.com/

I would really like to see that finished :\

> So ... if pgmap accounting was removed from gup-fast then this patch
> would be a lot simpler and we could perhaps just fallback to the regular
> hugepage case (THP, HugeTLB) like your suggestion at the top. See at the
> end below scissors mark as the ballpark of changes.
> 
> So far my options seem to be: 1) this patch which leverages the existing
> iteration logic or 2) switching to for_each_compound_range() -- see my previous
> reply 3) waiting for Dan to remove @pgmap accounting in gup-fast and use
> something similar to below scissors mark.
> 
> What do you think would be the best course of action?

I still think the basic algorithm should be to accumulate physicaly
contiguous addresses when walking the page table and then flush them
back to struct pages once we can't accumulate any more.

That works for both the walkers and all the page types?

If the get_dev_pagemap has to remain then it just means we have to
flush before changing pagemap pointers

Jason

  reply	other threads:[~2021-09-28 18:01 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 14:58 [PATCH v4 00/14] mm, sparse-vmemmap: Introduce compound devmaps for device-dax Joao Martins
2021-08-27 14:58 ` [PATCH v4 01/14] memory-failure: fetch compound_head after pgmap_pfn_valid() Joao Martins
2021-08-27 14:58 ` [PATCH v4 02/14] mm/page_alloc: split prep_compound_page into head and tail subparts Joao Martins
2021-08-27 14:58 ` [PATCH v4 03/14] mm/page_alloc: refactor memmap_init_zone_device() page init Joao Martins
2021-08-27 14:58 ` [PATCH v4 04/14] mm/memremap: add ZONE_DEVICE support for compound pages Joao Martins
2021-08-27 15:33   ` Christoph Hellwig
2021-08-27 16:00     ` Joao Martins
2021-09-01  9:44       ` Christoph Hellwig
2021-09-09  9:38         ` Joao Martins
2021-08-27 14:58 ` [PATCH v4 05/14] device-dax: use ALIGN() for determining pgoff Joao Martins
2021-08-27 14:58 ` [PATCH v4 06/14] device-dax: ensure dev_dax->pgmap is valid for dynamic devices Joao Martins
2021-11-05  0:31   ` Dan Williams
2021-11-05 12:09     ` Joao Martins
2021-11-05 16:14       ` Joao Martins
2021-11-05 16:46       ` Dan Williams
2021-11-05 18:11         ` Joao Martins
2021-08-27 14:58 ` [PATCH v4 07/14] device-dax: compound devmap support Joao Martins
2021-11-05  0:38   ` Dan Williams
2021-11-05 14:10     ` Joao Martins
2021-11-05 16:41       ` Dan Williams
2021-08-27 14:58 ` [PATCH v4 08/14] mm/gup: grab head page refcount once for group of subpages Joao Martins
2021-08-27 16:25   ` Jason Gunthorpe
2021-08-27 18:34     ` Joao Martins
2021-08-30 13:07       ` Jason Gunthorpe
2021-08-31 12:34         ` Joao Martins
2021-08-31 17:05           ` Jason Gunthorpe
2021-09-23 16:51             ` Joao Martins
2021-09-28 18:01               ` Jason Gunthorpe [this message]
2021-09-29 11:50                 ` Joao Martins
2021-09-29 19:34                   ` Jason Gunthorpe
2021-09-30  3:01                     ` Alistair Popple
2021-09-30 17:54                       ` Joao Martins
2021-09-30 21:55                         ` Jason Gunthorpe
2021-10-18 18:36                       ` Jason Gunthorpe
2021-10-18 18:37                   ` Jason Gunthorpe
2021-10-08 11:54   ` Jason Gunthorpe
2021-10-11 15:53     ` Joao Martins
2021-10-13 17:41       ` Jason Gunthorpe
2021-10-13 19:18         ` Joao Martins
2021-10-13 19:43           ` Jason Gunthorpe
2021-10-14 17:56             ` Joao Martins
2021-10-14 18:06               ` Jason Gunthorpe
2021-08-27 14:58 ` [PATCH v4 09/14] mm/sparse-vmemmap: add a pgmap argument to section activation Joao Martins
2021-08-27 14:58 ` [PATCH v4 10/14] mm/sparse-vmemmap: refactor core of vmemmap_populate_basepages() to helper Joao Martins
2021-08-27 14:58 ` [PATCH v4 11/14] mm/hugetlb_vmemmap: move comment block to Documentation/vm Joao Martins
2021-08-27 14:58 ` [PATCH v4 12/14] mm/sparse-vmemmap: populate compound devmaps Joao Martins
2021-08-27 14:58 ` [PATCH v4 13/14] mm/page_alloc: reuse tail struct pages for " Joao Martins
2021-08-27 14:58 ` [PATCH v4 14/14] mm/sparse-vmemmap: improve memory savings for compound pud geometry Joao Martins

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