From: Eric Dumazet <eric.dumazet@gmail.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>,
"H. Peter Anvin" <hpa@linux.intel.com>,
linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v2 10/10] thp: implement refcounting for huge zero page
Date: Mon, 10 Sep 2012 16:48:07 +0200 [thread overview]
Message-ID: <1347288487.1234.1692.camel@edumazet-glaptop> (raw)
In-Reply-To: <20120910144438.GA31697@otc-wbsnb-06>
On Mon, 2012-09-10 at 17:44 +0300, Kirill A. Shutemov wrote:
> On Mon, Sep 10, 2012 at 04:02:39PM +0200, Eric Dumazet wrote:
> > On Mon, 2012-09-10 at 16:13 +0300, Kirill A. Shutemov wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > >
> > > H. Peter Anvin doesn't like huge zero page which sticks in memory forever
> > > after the first allocation. Here's implementation of lockless refcounting
> > > for huge zero page.
> > >
> > ...
> >
> > > +static unsigned long get_huge_zero_page(void)
> > > +{
> > > + struct page *zero_page;
> > > +retry:
> > > + if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
> > > + return ACCESS_ONCE(huge_zero_pfn);
> > > +
> > > + zero_page = alloc_pages(GFP_TRANSHUGE | __GFP_ZERO, HPAGE_PMD_ORDER);
> > > + if (!zero_page)
> > > + return 0;
> > > + if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
> > > + __free_page(zero_page);
> > > + goto retry;
> > > + }
> >
> > This might break if preemption can happen here ?
> >
> > The second thread might loop forever because huge_zero_refcount is 0,
> > and huge_zero_pfn not zero.
>
> I fail to see why the second thread might loop forever. Long time yes, but
> forever?
>
> Yes, disabling preemption before alloc_pages() and enabling after
> atomic_set() looks reasonable. Thanks.
If you have one online cpu, and the second thread is real time or
something like that, it wont give cpu back to preempted thread.
next prev parent reply other threads:[~2012-09-10 14:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-10 13:13 [PATCH v2 00/10] Introduce huge zero page Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 01/10] thp: huge zero page: basic preparation Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 02/10] thp: zap_huge_pmd(): zap huge zero pmd Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 03/10] thp: copy_huge_pmd(): copy huge zero page Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 04/10] thp: do_huge_pmd_wp_page(): handle " Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 05/10] thp: change_huge_pmd(): keep huge zero page write-protected Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 06/10] thp: change split_huge_page_pmd() interface Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 07/10] thp: implement splitting pmd for huge zero page Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 08/10] thp: setup huge zero page on non-write page fault Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 09/10] thp: lazy huge zero page allocation Kirill A. Shutemov
2012-09-10 13:13 ` [PATCH v2 10/10] thp: implement refcounting for huge zero page Kirill A. Shutemov
2012-09-10 14:02 ` Eric Dumazet
2012-09-10 14:44 ` Kirill A. Shutemov
2012-09-10 14:48 ` Eric Dumazet [this message]
2012-09-10 14:50 ` Kirill A. Shutemov
2012-09-10 14:57 ` Eric Dumazet
2012-09-10 15:07 ` Kirill A. Shutemov
2012-09-12 10:07 ` [PATCH v3 " Kirill A. Shutemov
2012-09-13 17:16 ` Andrea Arcangeli
2012-09-13 17:37 ` Kirill A. Shutemov
2012-09-13 21:17 ` Andrea Arcangeli
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