nvdimm.lists.linux.dev archive mirror
 help / color / mirror / Atom feed
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: Mon, 18 Oct 2021 15:37:49 -0300	[thread overview]
Message-ID: <20211018183749.GE3686969@ziepe.ca> (raw)
In-Reply-To: <3f35cc33-7012-5230-a771-432275e6a21e@oracle.com>

On Wed, Sep 29, 2021 at 12:50:15PM +0100, Joao Martins wrote:
> On 9/28/21 19:01, Jason Gunthorpe wrote:
> > On Thu, Sep 23, 2021 at 05:51:04PM +0100, Joao Martins wrote:
> >> 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?
> > 
> 
> The logic already handles all page types -- I was trying to avoid the extra
> complexity in regular hugetlb/THP path by not merging the handling of the
> oddball case that is devmap (or fundamentally devmap
> non-compound case in the future).

FYI, this untested thing is what I came to when I tried to make
something like this:

/*
 * A large page entry such as PUD/PMD can point to a struct page. In cases like
 * THP this struct page will be a compound page of the same order as the page
 * table level. However, in cases like DAX or more generally pgmap ZONE_DEVICE,
 * the PUD/PMD may point at the first pfn in a string of pages.
 *
 * This helper iterates over all head pages or all the non-compound base pages.
 */
static pt_entry_iter_state
{
	struct page *head;
	unsigned long compound_nr;
	unsigned long pfn;
	unsigned long end_pfn;
};

static inline struct page *__pt_start_iter(struct iter_state *state,
					   struct page *page, unsigned long pfn,
					   unsigned int entry_size)
{
	state->head = compound_head(page);
	state->compound_nr = compound_nr(page);
	state->pfn = pfn & (~(state->compound_nr - 1));
	state->end_pfn = pfn + entry_size / PAGE_SIZE;
	return state->head;
}

static inline struct page *__pt_next_page(struct iter_state *state)
{
	state->pfn += state->compound_nr;
	if (state->end_pfn <= state->pfn)
		return NULL;
	state->head = pfn_to_page(state->pfn);
	state->compound_nr = compound_nr(page);
	return state->head;
}

#define for_each_page_in_pt_entry(state, page, pfn, entry_size)                \
	for (page = __pt_start_iter(state, page, pfn, entry_size); page;       \
	     page = __pt_next_page(&state))

static bool remove_pages_from_page_table(struct vm_area_struct *vma,
					 struct page *page, unsigned long pfn,
					 unsigned int entry_size, bool is_dirty,
					 bool is_young)
{
	struct iter_state state;

	for_each_page_in_pt_entry(&state, page, pfn, entry_size)
		remove_page_from_page_table(vma, page, is_dirty, is_young);
}


Jason

  parent reply	other threads:[~2021-10-18 18:37 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211018183749.GE3686969@ziepe.ca \
    --to=jgg@ziepe.ca \
    --cc=akpm@linux-foundation.org \
    --cc=corbet@lwn.net \
    --cc=dan.j.williams@intel.com \
    --cc=dave.jiang@intel.com \
    --cc=hch@lst.de \
    --cc=jane.chu@oracle.com \
    --cc=jhubbard@nvidia.com \
    --cc=joao.m.martins@oracle.com \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mike.kravetz@oracle.com \
    --cc=naoya.horiguchi@nec.com \
    --cc=nvdimm@lists.linux.dev \
    --cc=songmuchun@bytedance.com \
    --cc=vishal.l.verma@intel.com \
    --cc=willy@infradead.org \
    --subject='Re: [PATCH v4 08/14] mm/gup: grab head page refcount once for group of subpages' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).