On Fri 31-01-20 19:40:26, John Hubbard wrote:

As part of pin_user_pages() and related API calls, pages are "dma-pinned". For the case of compound pages of order > 1, the per-page accounting of dma pins is accomplished via the 3rd struct page in the compound page. In order to support debugging of any pin_user_pages()- related problems, enhance dump_page() so as to report the pin count in that case.

Documentation/core-api/pin_user_pages.rst is also updated accordingly.

Signed-off-by: John Hubbard jhubbard@nvidia.com

Looks good to me. You can add:

Reviewed-by: Jan Kara jack@suse.cz

Honza

---

Documentation/core-api/pin_user_pages.rst | 7 +++++ mm/debug.c | 34 +++++++++++++++++------ 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index 3f72b1ea1104..dd21ea140ef4 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -215,6 +215,13 @@ Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is because there is a noticeable performance drop in unpin_user_page(), when they are activated. +Other diagnostics +=================

+dump_page() has been enhanced slightly, to handle these new counting fields, and +to better report on compound pages in general. Specifically, for compound pages +with order > 1, the exact (hpage_pinned_refcount) pincount is reported.

References

diff --git a/mm/debug.c b/mm/debug.c index beb1c59d784b..db81b11345be 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -57,10 +57,20 @@ static void __dump_tail_page(struct page *page, int mapcount) page, page_ref_count(page), mapcount, page->mapping, page_to_pgoff(page)); } else {

• pr_warn("page:%px compound refcount:%d mapcount:%d mapping:%px "
  

• 	"index:%#lx compound_mapcount:%d\n",
  

• 	page, page_ref_count(head), mapcount, head->mapping,
  

• 	page_to_pgoff(head), compound_mapcount(page));
  

• if (hpage_pincount_available(page))
  

• 	pr_warn("page:%px compound refcount:%d mapcount:%d "
  

• 		"mapping:%px index:%#lx compound_mapcount:%d "
  

• 		"compound_pincount:%d\n",
  

• 		page, page_ref_count(head), mapcount,
  

• 		head->mapping, page_to_pgoff(head),
  

• 		compound_mapcount(page),
  

• 		compound_pincount(page));
  

• else
  

• 	pr_warn("page:%px compound refcount:%d mapcount:%d "
  

• 		"mapping:%px index:%#lx compound_mapcount:%d\n",
  

• 		page, page_ref_count(head), mapcount,
  

• 		head->mapping, page_to_pgoff(head),
  

• 		compound_mapcount(page));
  

  }

if (page_ref_count(page) != 0) @@ -103,10 +113,18 @@ void __dump_page(struct page *page, const char *reason) if (PageTail(page)) __dump_tail_page(page, mapcount);

• else

• pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
  

• 	page, page_ref_count(page), mapcount,
  

• 	page->mapping, page_to_pgoff(page));
  

• else {

• if (hpage_pincount_available(page))
  

• 	pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
  

• 		"index:%#lx compound pincount: %d\n",
  

• 		page, page_ref_count(page), mapcount,
  

• 		page->mapping, page_to_pgoff(page),
  

• 		compound_pincount(page));
  

• else
  

• 	pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
  

• 		"index:%#lx\n", page, page_ref_count(page),
  

• 		mapcount, page->mapping, page_to_pgoff(page));
  

• } if (PageKsm(page)) type = "ksm "; else if (PageAnon(page))

-- 2.25.0