From: John Hubbard <jhubbard@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Dave Chinner" <david@fromorbit.com>,
"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v5 01/12] mm: dump_page(): better diagnostics for compound pages
Date: Fri, 7 Feb 2020 13:05:52 -0800 [thread overview]
Message-ID: <3477bf65-64dc-7854-6720-589f7fcdac07@nvidia.com> (raw)
In-Reply-To: <20200207172746.GE8731@bombadil.infradead.org>
On 2/7/20 9:27 AM, Matthew Wilcox wrote:
...
>
> A definite improvement, but I think we could do better. For example,
> you've changed PageCompound to PageTail here, whereas we really do want
> to dump some more information for PageHead pages than the plain vanilla
> order-0 page has. Another thing is that page_mapping() calls compound_head(),
> so if the page is corrupted, we're going to get a funky pointer dereference.
>
> I spent a bit of time on this reimplementation ... what do you think?
>
It looks fine to me. I gave it a quick spin, here's the output for a normal
and a huge page, and it has everything we want to see:
page:ffffea0010f0d640 refcount:1025 mapcount:1 mapping:0000000021857089 index:0xed
anon flags: 0x17ffe0000080036(referenced|uptodate|lru|active|swapbacked)
raw: 017ffe0000080036 ffffea0011731f08 ffffea0011730008 ffff8884777272c1
raw: 00000000000000ed 0000000000000000 0000040100000000 0000000000000000
page dumped because: testing dump_page()
page:ffffea0010ef1b80 head:ffffea0010ef0000 refcount:0 mapcount:1 mapping:00000000a8e1c7fa index:0xed order:9 compound_mapcount: 1
anon flags: 0x17ffe0000000000()
raw: 017ffe0000000000 ffffea0010ef0001 ffffea0010ef1b88 dead000000000400
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
head: 017ffe0000090036 ffffea0011734548 ffffea0010ef8008 ffff8884777271b9
head: 000000000000007f 0000000000000000 00000201ffffffff 0000000000000000
page dumped because: testing dump_page()
> - Print the mapping pointer using %p insted of %px. The actual value of
> the pointer can be read out of the raw page dump and using %p gives a
> chance to correlate it to earlier printk of the mapping pointer.
> - Add the order of the page for compound pages
> - Dump the raw head page as well as the raw page being dumped
>
> diff --git a/mm/debug.c b/mm/debug.c
> index ecccd9f17801..0564d4cb8233 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -44,8 +44,10 @@ const struct trace_print_flags vmaflag_names[] = {
>
> void __dump_page(struct page *page, const char *reason)
> {
> + struct page *head = compound_head(page);
> struct address_space *mapping;
> bool page_poisoned = PagePoisoned(page);
> + bool compound = PageCompound(page);
> /*
> * Accessing the pageblock without the zone lock. It could change to
> * "isolate" again in the meantime, but since we are just dumping the
> @@ -66,25 +68,32 @@ void __dump_page(struct page *page, const char *reason)
> goto hex_only;
> }
>
> - mapping = page_mapping(page);
> + if (page < head || (page >= head + MAX_ORDER_NR_PAGES)) {
> + /* Corrupt page, cannot call page_mapping */
> + mapping = page->mapping;
> + head = page;
> + compound = false;
> + } else {
> + mapping = page_mapping(page);
> + }
>
> /*
> * Avoid VM_BUG_ON() in page_mapcount().
> * page->_mapcount space in struct page is used by sl[aou]b pages to
> * encode own info.
> */
> - mapcount = PageSlab(page) ? 0 : page_mapcount(page);
> + mapcount = PageSlab(head) ? 0 : page_mapcount(head);
>
> - if (PageCompound(page))
> - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
> - "index:%#lx compound_mapcount: %d\n",
> - page, page_ref_count(page), mapcount,
> + if (compound)
> + pr_warn("page:%px head:%px refcount:%d mapcount:%d mapping:%p "
> + "index:%#lx order:%u compound_mapcount: %d\n",
> + page, head, page_ref_count(page), mapcount,
> page->mapping, page_to_pgoff(page),
> - compound_mapcount(page));
> + compound_order(head), compound_mapcount(page));
> else
> - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
> + pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n",
> page, page_ref_count(page), mapcount,
> - page->mapping, page_to_pgoff(page));
> + mapping, page_to_pgoff(page));
> if (PageKsm(page))
> type = "ksm ";
> else if (PageAnon(page))
> @@ -106,6 +115,10 @@ void __dump_page(struct page *page, const char *reason)
> print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
> sizeof(unsigned long), page,
> sizeof(struct page), false);
> + if (!page_poisoned && compound)
> + print_hex_dump(KERN_WARNING, "head: ", DUMP_PREFIX_NONE, 32,
> + sizeof(unsigned long), head,
> + sizeof(struct page), false);
Good thought to get the hex dump of the head page in this case, yes.
>
> if (reason)
> pr_warn("page dumped because: %s\n", reason);
>
Seeing as how I want to further enhance dump_page() slightly for this series (to
include the 3rd struct page's hpage_pincount), would you care to send this as a
formal patch that I could insert into this series, to replace patch 5?
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2020-02-07 21:05 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 3:37 [PATCH v5 00/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-07 3:37 ` [PATCH v5 01/12] mm: dump_page(): better diagnostics for compound pages John Hubbard
2020-02-07 17:27 ` Matthew Wilcox
2020-02-07 21:05 ` John Hubbard [this message]
2020-02-07 21:14 ` John Hubbard
2020-02-07 3:37 ` [PATCH v5 02/12] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-02-07 3:37 ` [PATCH v5 03/12] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-02-07 3:37 ` [PATCH v5 04/12] mm: introduce page_ref_sub_return() John Hubbard
2020-02-07 13:18 ` Kirill A. Shutemov
2020-02-07 3:37 ` [PATCH v5 05/12] mm/gup: pass gup flags to two more routines John Hubbard
2020-02-07 3:37 ` [PATCH v5 06/12] mm/gup: require FOLL_GET for get_user_pages_fast() John Hubbard
2020-02-07 3:37 ` [PATCH v5 07/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-07 3:37 ` [PATCH v5 08/12] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-02-07 3:37 ` [PATCH v5 09/12] mm: dump_page(): better diagnostics for huge pinned pages John Hubbard
2020-02-07 3:37 ` [PATCH v5 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-02-07 13:19 ` Kirill A. Shutemov
2020-02-10 10:16 ` Jan Kara
2020-02-10 17:07 ` John Hubbard
2020-02-07 3:37 ` [PATCH v5 11/12] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-02-07 3:37 ` [PATCH v5 12/12] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
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