From: Mike Kravetz <mike.kravetz@oracle.com>
To: Pasha Tatashin <pasha.tatashin@soleen.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-m68k@lists.linux-m68k.org, anshuman.khandual@arm.com,
willy@infradead.org, akpm@linux-foundation.org,
william.kucharski@oracle.com, vbabka@suse.cz,
geert@linux-m68k.org, schmitzmic@gmail.com, rostedt@goodmis.org,
mingo@redhat.com, hannes@cmpxchg.org, guro@fb.com,
songmuchun@bytedance.com, weixugc@google.com, gthelen@google.com
Subject: Re: [RFC 2/8] mm/hugetlb: remove useless set_page_count()
Date: Tue, 26 Oct 2021 11:44:17 -0700 [thread overview]
Message-ID: <57fbf167-b2e8-69f6-7f79-8e989162c889@oracle.com> (raw)
In-Reply-To: <20211026173822.502506-3-pasha.tatashin@soleen.com>
On 10/26/21 10:38 AM, Pasha Tatashin wrote:
> prep_compound_gigantic_page() calls set_page_count(0, p), but it is not
> needed because page_ref_freeze(p, 1) already sets refcount to 0.
>
> Using, set_page_count() is dangerous, because it unconditionally resets
> refcount from the current value to unrestrained value, and therefore
> should be minimized.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Thanks!
My bad for not removing the set_page_count when adding the page_ref_freeze.
FYI, there have been additional changes to this routine in Andrew's
tree. Not really sure if we want/need the VM_BUG_ON_PAGE as that would
only check if there was a 'bug' in page_ref_freeze.
--
Mike Kravetz
> ---
> mm/hugetlb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 95dc7b83381f..7e3996c8b696 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1707,7 +1707,7 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
> pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
> goto out_error;
> }
> - set_page_count(p, 0);
> + VM_BUG_ON_PAGE(page_count(p), p);
> set_compound_head(p, page);
> }
> atomic_set(compound_mapcount_ptr(page), -1);
>
next prev parent reply other threads:[~2021-10-26 18:45 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-26 17:38 [RFC 0/8] Hardening page _refcount Pasha Tatashin
2021-10-26 17:38 ` [RFC 1/8] mm: add overflow and underflow checks for page->_refcount Pasha Tatashin
2021-10-26 19:48 ` Matthew Wilcox
2021-10-26 21:34 ` Pasha Tatashin
2021-10-27 1:21 ` Pasha Tatashin
2021-10-27 3:04 ` Matthew Wilcox
2021-10-27 18:22 ` Pasha Tatashin
2021-10-27 7:46 ` Muchun Song
2021-10-27 18:22 ` Pasha Tatashin
2021-10-28 4:08 ` Muchun Song
2021-10-26 17:38 ` [RFC 2/8] mm/hugetlb: remove useless set_page_count() Pasha Tatashin
2021-10-26 18:44 ` Mike Kravetz [this message]
2021-10-26 18:50 ` Pasha Tatashin
2021-10-26 21:19 ` Mike Kravetz
2021-10-26 17:38 ` [RFC 3/8] mm: Avoid using set_page_count() in set_page_recounted() Pasha Tatashin
2021-10-26 17:53 ` John Hubbard
2021-10-26 18:01 ` John Hubbard
2021-10-26 18:14 ` Pasha Tatashin
2021-10-26 18:21 ` Pasha Tatashin
2021-10-27 5:12 ` John Hubbard
2021-10-27 18:27 ` Pasha Tatashin
2021-10-28 1:20 ` John Hubbard
2021-10-28 1:35 ` John Hubbard
2021-11-01 14:30 ` Pasha Tatashin
2021-11-01 19:35 ` John Hubbard
2021-11-01 14:22 ` Pasha Tatashin
2021-11-01 19:31 ` John Hubbard
2021-11-01 19:42 ` John Hubbard
2021-10-26 17:38 ` [RFC 4/8] mm: remove set_page_count() from page_frag_alloc_align Pasha Tatashin
2021-10-26 17:38 ` [RFC 5/8] mm: avoid using set_page_count() when pages are freed into allocator Pasha Tatashin
2021-10-26 17:38 ` [RFC 6/8] mm: rename init_page_count() -> page_ref_init() Pasha Tatashin
2021-10-27 6:46 ` Geert Uytterhoeven
2021-10-26 17:38 ` [RFC 7/8] mm: remove set_page_count() Pasha Tatashin
2021-10-26 17:38 ` [RFC 8/8] mm: simplify page_ref_* functions Pasha Tatashin
2021-10-26 18:23 ` [RFC 0/8] Hardening page _refcount Matthew Wilcox
2021-10-26 18:30 ` Pasha Tatashin
2021-10-26 20:13 ` Matthew Wilcox
2021-10-26 21:24 ` Pasha Tatashin
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