From: Christoph Lameter <cl@linux.com>
To: Pravin Shelar <pshelar@nicira.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
penberg@kernel.org, mpm@selenic.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
jesse@nicira.com, abhide@nicira.com
Subject: Re: [PATCH] mm: sl[auo]b: Use atomic bit operations to update page-flags.
Date: Wed, 9 May 2012 12:25:24 -0500 (CDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1205091224460.11225@router.home> (raw)
In-Reply-To: <CALnjE+pExzAS4bk89RD4XJtHtSyB2g0qMsqdrGWPuD27axiNBw@mail.gmail.com>
On Wed, 9 May 2012, Pravin Shelar wrote:
> On Tue, May 8, 2012 at 12:22 PM, Christoph Lameter <cl@linux.com> wrote:
> > On Tue, 8 May 2012, Eric Dumazet wrote:
> >
> >> On Tue, 2012-05-08 at 11:55 -0700, Pravin B Shelar wrote:
> >> > Transparent huge pages can change page->flags (PG_compound_lock)
> >> > without taking Slab lock. So sl[auo]b need to use atomic bit
> >> > operation while changing page->flags.
> >> > Specificly this patch fixes race between compound_unlock and slab
> >> > functions which does page-flags update. This can occur when
> >> > get_page/put_page is called on page from slab object.
> >>
> >>
> >> But should get_page()/put_page() be called on a page own by slub ?
> >
> > Can occur in slab allocators if the slab memory is used for DMA. I dont
> > like the performance impact of the atomics. In particular slab_unlock() in
> > slub is or used to be a hot path item. It is still hot on arches that do
> > not support this_cpu_cmpxchg_double. With the cmpxchg_double only the
> > debug mode is affected.
> >
>
> I agree this would impact performance. I am not sure how else we can
> fix this issue. As far as slab_unlock in hot path case is concerned,
> it is more likely to corrupt page->flags in that case.
Dont modify any page flags from THP logic if its a slab page? THP cannot
break up or merge slab pages anyways.
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next prev parent reply other threads:[~2012-05-09 17:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-08 18:55 Pravin B Shelar
2012-05-08 19:11 ` Eric Dumazet
2012-05-08 19:22 ` Christoph Lameter
2012-05-09 16:41 ` Pravin Shelar
2012-05-09 17:25 ` Christoph Lameter [this message]
2012-05-09 18:34 ` Pravin Shelar
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