From: David Hildenbrand <david@redhat.com>
To: Lance Yang <ioworker0@gmail.com>
Cc: akpm@linux-foundation.org, cgroups@vger.kernel.org,
chris@zankel.net, corbet@lwn.net, dalias@libc.org,
fengwei.yin@intel.com, glaubitz@physik.fu-berlin.de,
hughd@google.com, jcmvbkbc@gmail.com, linmiaohe@huawei.com,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
muchun.song@linux.dev, naoya.horiguchi@nec.com,
peterx@redhat.com, richardycc@google.com, ryan.roberts@arm.com,
shy828301@gmail.com, willy@infradead.org,
ysato@users.sourceforge.jp, ziy@nvidia.com
Subject: Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios
Date: Tue, 16 Apr 2024 12:47:07 +0200 [thread overview]
Message-ID: <3ef81fe3-2584-4db8-ab66-eaa44c035707@redhat.com> (raw)
In-Reply-To: <20240416104008.41979-1-ioworker0@gmail.com>
On 16.04.24 12:40, Lance Yang wrote:
> Hey David,
>
> Maybe I spotted a bug below.
Thanks for the review!
>
> [...]
> static inline bool folio_likely_mapped_shared(struct folio *folio)
> {
> - return page_mapcount(folio_page(folio, 0)) > 1;
> + int mapcount = folio_mapcount(folio);
> +
> + /* Only partially-mappable folios require more care. */
> + if (!folio_test_large(folio) || unlikely(folio_test_hugetlb(folio)))
> + return mapcount > 1;
> +
> + /* A single mapping implies "mapped exclusively". */
> + if (mapcount <= 1)
> + return false;
> +
> + /* If any page is mapped more than once we treat it "mapped shared". */
> + if (folio_entire_mapcount(folio) || mapcount > folio_nr_pages(folio))
> + return true;
>
> bug: if a PMD-mapped THP is exclusively mapped, the folio_entire_mapcount()
> function will return 1 (atomic_read(&folio->_entire_mapcount) + 1).
If it's exclusively mapped, then folio_mapcount(folio)==1. In which case
the previous statement:
if (mapcount <= 1)
return false;
Catches it.
IOW, once we reach this point we now that folio_mapcount(folio) > 1, and
there must be something else besides the entire mapping ("more than once").
Or did I not address your concern?
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2024-04-16 10:47 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-09 19:22 [PATCH v1 00/18] mm: mapcount for large folios + page_mapcount() cleanups David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 01/18] mm: allow for detecting underflows with page_mapcount() again David Hildenbrand
2024-04-09 20:06 ` Zi Yan
2024-04-09 21:42 ` Matthew Wilcox
2024-04-10 8:10 ` David Hildenbrand
2024-04-24 9:38 ` David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 02/18] mm/rmap: always inline anon/file rmap duplication of a single PTE David Hildenbrand
2024-04-19 2:25 ` Yin, Fengwei
2024-04-19 9:14 ` David Hildenbrand
2024-04-19 14:01 ` Yin, Fengwei
2024-04-09 19:22 ` [PATCH v1 03/18] mm/rmap: add fast-path for small folios when adding/removing/duplicating David Hildenbrand
2024-04-19 14:02 ` Yin, Fengwei
2024-04-09 19:22 ` [PATCH v1 04/18] mm: track mapcount of large folios in single value David Hildenbrand
2024-04-09 20:13 ` Zi Yan
2024-04-10 8:20 ` David Hildenbrand
2024-04-18 14:50 ` Lance Yang
2024-04-18 15:09 ` David Hildenbrand
2024-04-19 0:31 ` Lance Yang
2024-04-19 14:02 ` Yin, Fengwei
2024-04-09 19:22 ` [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios David Hildenbrand
2024-04-16 10:40 ` Lance Yang
2024-04-16 10:47 ` David Hildenbrand [this message]
2024-04-16 10:52 ` Lance Yang
2024-04-16 10:53 ` David Hildenbrand
2024-04-19 2:29 ` Yin, Fengwei
2024-04-19 9:19 ` David Hildenbrand
2024-04-19 13:47 ` Yin, Fengwei
2024-04-19 13:48 ` David Hildenbrand
2024-04-19 14:03 ` Yin, Fengwei
2024-04-09 19:22 ` [PATCH v1 06/18] mm: make folio_mapcount() return 0 for small typed folios David Hildenbrand
2024-04-24 9:40 ` David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 07/18] mm/memory: use folio_mapcount() in zap_present_folio_ptes() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 08/18] mm/huge_memory: use folio_mapcount() in zap_huge_pmd() sanity check David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 09/18] mm/memory-failure: use folio_mapcount() in hwpoison_user_mappings() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 10/18] mm/page_alloc: use folio_mapped() in __alloc_contig_migrate_range() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 11/18] mm/migrate: use folio_likely_mapped_shared() in add_page_for_migration() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 12/18] sh/mm/cache: use folio_mapped() in copy_from_user_page() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 13/18] mm/filemap: use folio_mapcount() in filemap_unaccount_folio() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 14/18] mm/migrate_device: use folio_mapcount() in migrate_vma_check_page() David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 15/18] trace/events/page_ref: trace the raw page mapcount value David Hildenbrand
2024-04-09 19:22 ` [PATCH v1 16/18] xtensa/mm: convert check_tlb_entry() to sanity check folios David Hildenbrand
2024-04-09 19:23 ` [PATCH v1 17/18] mm/debug: print only page mapcount (excluding folio entire mapcount) in __dump_folio() David Hildenbrand
2024-04-09 19:23 ` [PATCH v1 18/18] Documentation/admin-guide/cgroup-v1/memory.rst: don't reference page_mapcount() David Hildenbrand
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=3ef81fe3-2584-4db8-ab66-eaa44c035707@redhat.com \
--to=david@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=cgroups@vger.kernel.org \
--cc=chris@zankel.net \
--cc=corbet@lwn.net \
--cc=dalias@libc.org \
--cc=fengwei.yin@intel.com \
--cc=glaubitz@physik.fu-berlin.de \
--cc=hughd@google.com \
--cc=ioworker0@gmail.com \
--cc=jcmvbkbc@gmail.com \
--cc=linmiaohe@huawei.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-sh@vger.kernel.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=muchun.song@linux.dev \
--cc=naoya.horiguchi@nec.com \
--cc=peterx@redhat.com \
--cc=richardycc@google.com \
--cc=ryan.roberts@arm.com \
--cc=shy828301@gmail.com \
--cc=willy@infradead.org \
--cc=ysato@users.sourceforge.jp \
--cc=ziy@nvidia.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).