From: Nick Piggin <npiggin@suse.de>
To: Christoph Lameter <clameter@sgi.com>
Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
benh@kernel.crashing.org, paulus@samba.org
Subject: Re: [patch 7/7] powerpc: lockless get_user_pages_fast
Date: Wed, 11 Jun 2008 06:47:16 +0200 [thread overview]
Message-ID: <20080611044716.GA11545@wotan.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0806102138380.19967@schroedinger.engr.sgi.com>
On Tue, Jun 10, 2008 at 09:40:25PM -0700, Christoph Lameter wrote:
> On Wed, 11 Jun 2008, Nick Piggin wrote:
>
> > > This is reversing the modification to make get_page_unless_zero() usable
> > > with compound page heads. Will break the slab defrag patchset.
> >
> > Is the slab defrag patchset in -mm? Because you ignored my comment about
> > this change that assertions should not be weakened until required by the
> > actual patchset. I wanted to have these assertions be as strong as
> > possible for the lockless pagecache patchset.
>
> So you are worried about accidentally using get_page_unless_zero on a
> compound page? What would be wrong about that?
Unexpected. Compound pages should have no such races that require
get_page_unless_zero that we very carefully use in page reclaim.
If you don't actually know whether you have a reference to the
thing or not before trying to operate on it, then you're almost
definitely got refcount wrong. How does slab defrag use it?
WARNING: multiple messages have this Message-ID (diff)
From: Nick Piggin <npiggin@suse.de>
To: Christoph Lameter <clameter@sgi.com>
Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
benh@kernel.crashing.org, paulus@samba.org
Subject: Re: [patch 7/7] powerpc: lockless get_user_pages_fast
Date: Wed, 11 Jun 2008 06:47:16 +0200 [thread overview]
Message-ID: <20080611044716.GA11545@wotan.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.64.0806102138380.19967@schroedinger.engr.sgi.com>
On Tue, Jun 10, 2008 at 09:40:25PM -0700, Christoph Lameter wrote:
> On Wed, 11 Jun 2008, Nick Piggin wrote:
>
> > > This is reversing the modification to make get_page_unless_zero() usable
> > > with compound page heads. Will break the slab defrag patchset.
> >
> > Is the slab defrag patchset in -mm? Because you ignored my comment about
> > this change that assertions should not be weakened until required by the
> > actual patchset. I wanted to have these assertions be as strong as
> > possible for the lockless pagecache patchset.
>
> So you are worried about accidentally using get_page_unless_zero on a
> compound page? What would be wrong about that?
Unexpected. Compound pages should have no such races that require
get_page_unless_zero that we very carefully use in page reclaim.
If you don't actually know whether you have a reference to the
thing or not before trying to operate on it, then you're almost
definitely got refcount wrong. How does slab defrag use it?
--
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next prev parent reply other threads:[~2008-06-11 4:47 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-05 9:43 [patch 0/7] speculative page references, lockless pagecache, lockless gup npiggin
2008-06-05 9:43 ` npiggin
2008-06-05 9:43 ` [patch 1/7] mm: readahead scan lockless npiggin
2008-06-05 9:43 ` npiggin
2008-06-05 9:43 ` [patch 2/7] radix-tree: add gang_lookup_slot, gang_lookup_slot_tag npiggin
2008-06-05 9:43 ` npiggin
2008-06-05 9:43 ` [patch 3/7] mm: speculative page references npiggin
2008-06-05 9:43 ` npiggin
2008-06-06 14:20 ` Peter Zijlstra
2008-06-06 14:20 ` Peter Zijlstra
2008-06-06 16:26 ` Nick Piggin
2008-06-06 16:26 ` Nick Piggin
2008-06-06 16:27 ` Nick Piggin
2008-06-06 16:27 ` Nick Piggin
2008-06-09 4:48 ` Tim Pepper
2008-06-09 4:48 ` Tim Pepper
2008-06-10 19:08 ` Christoph Lameter
2008-06-10 19:08 ` Christoph Lameter
2008-06-11 3:19 ` Nick Piggin
2008-06-11 3:19 ` Nick Piggin
2008-06-05 9:43 ` [patch 4/7] mm: lockless pagecache npiggin
2008-06-05 9:43 ` npiggin
2008-06-05 9:43 ` [patch 5/7] mm: spinlock tree_lock npiggin
2008-06-05 9:43 ` npiggin
2008-06-05 9:43 ` [patch 6/7] powerpc: implement pte_special npiggin
2008-06-05 9:43 ` npiggin
2008-06-06 4:04 ` Benjamin Herrenschmidt
2008-06-06 4:04 ` Benjamin Herrenschmidt
2008-06-05 9:43 ` [patch 7/7] powerpc: lockless get_user_pages_fast npiggin
2008-06-05 9:43 ` npiggin
2008-06-09 8:32 ` Andrew Morton
2008-06-09 8:32 ` Andrew Morton
2008-06-10 3:15 ` Nick Piggin
2008-06-10 3:15 ` Nick Piggin
2008-06-10 19:00 ` Christoph Lameter
2008-06-10 19:00 ` Christoph Lameter
2008-06-11 3:18 ` Nick Piggin
2008-06-11 3:18 ` Nick Piggin
2008-06-11 4:40 ` Christoph Lameter
2008-06-11 4:40 ` Christoph Lameter
2008-06-11 4:41 ` Christoph Lameter
2008-06-11 4:41 ` Christoph Lameter
2008-06-11 4:49 ` Nick Piggin
2008-06-11 4:49 ` Nick Piggin
2008-06-11 6:06 ` Andrew Morton
2008-06-11 6:06 ` Andrew Morton
2008-06-11 6:24 ` Nick Piggin
2008-06-11 6:24 ` Nick Piggin
2008-06-11 6:50 ` Andrew Morton
2008-06-11 6:50 ` Andrew Morton
2008-06-11 23:20 ` Christoph Lameter
2008-06-11 23:20 ` Christoph Lameter
2008-06-11 4:47 ` Nick Piggin [this message]
2008-06-11 4:47 ` Nick Piggin
2008-06-05 11:53 ` [patch 0/7] speculative page references, lockless pagecache, lockless gup Nick Piggin
2008-06-05 11:53 ` Nick Piggin
2008-06-05 17:33 ` Linus Torvalds
2008-06-05 17:33 ` Linus Torvalds
2008-06-06 0:08 ` Nick Piggin
2008-06-06 0:08 ` Nick Piggin
2008-06-06 21:32 ` Peter Zijlstra
2008-06-06 21:32 ` Peter Zijlstra
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