From: Namhyung Kim <namhyung@gmail.com>
To: Christoph Lameter <cl@gentwo.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>,
Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] slub: set PG_slab on all of slab pages
Date: Thu, 01 Mar 2012 16:30:31 +0900 [thread overview]
Message-ID: <1330587031.1762.46.camel@leonhard> (raw)
In-Reply-To: <alpine.DEB.2.00.1202290922210.32268@router.home>
Hi,
2012-02-29, 09:24 -0600, Christoph Lameter wrote:
> On Wed, 29 Feb 2012, Namhyung Kim wrote:
>
> > Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
> > call free_pages() incorrectly on a object in a tail page, she will get
> > confused with the undefined result. Setting the flag would help her by
> > emitting a warning on bad_page() in such a case.
>
> NAK
>
> You cannot free a tail page of a compound higher order page independently.
> You must free the whole compound.
>
I meant freeing a *slab object* resides in a compound page using buddy
system API (e.g. free_pages). I know it's definitely a programming
error. However there's no safety net to protect and/or warn such a
misbehavior AFAICS - except for head page which has PG_slab set - when
it happened by any chance.
Without it, it might be possible to free part of tail pages silently,
and cause unexpected not-so-funny results some time later. It should be
hard to find out.
When I ran such a bad code using SLAB, I was able to be notified
immediately. That's why I'd like to add this patch to SLUB too. In
addition, it will give more correct value for slab pages when
using /proc/kpageflags IMHO.
--
Regards,
Namhyung Kim
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WARNING: multiple messages have this Message-ID (diff)
From: Namhyung Kim <namhyung@gmail.com>
To: Christoph Lameter <cl@gentwo.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>,
Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] slub: set PG_slab on all of slab pages
Date: Thu, 01 Mar 2012 16:30:31 +0900 [thread overview]
Message-ID: <1330587031.1762.46.camel@leonhard> (raw)
In-Reply-To: <alpine.DEB.2.00.1202290922210.32268@router.home>
Hi,
2012-02-29, 09:24 -0600, Christoph Lameter wrote:
> On Wed, 29 Feb 2012, Namhyung Kim wrote:
>
> > Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
> > call free_pages() incorrectly on a object in a tail page, she will get
> > confused with the undefined result. Setting the flag would help her by
> > emitting a warning on bad_page() in such a case.
>
> NAK
>
> You cannot free a tail page of a compound higher order page independently.
> You must free the whole compound.
>
I meant freeing a *slab object* resides in a compound page using buddy
system API (e.g. free_pages). I know it's definitely a programming
error. However there's no safety net to protect and/or warn such a
misbehavior AFAICS - except for head page which has PG_slab set - when
it happened by any chance.
Without it, it might be possible to free part of tail pages silently,
and cause unexpected not-so-funny results some time later. It should be
hard to find out.
When I ran such a bad code using SLAB, I was able to be notified
immediately. That's why I'd like to add this patch to SLUB too. In
addition, it will give more correct value for slab pages when
using /proc/kpageflags IMHO.
--
Regards,
Namhyung Kim
next prev parent reply other threads:[~2012-03-01 7:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-29 8:54 [PATCH -next] slub: set PG_slab on all of slab pages Namhyung Kim
2012-02-29 8:54 ` Namhyung Kim
2012-02-29 15:24 ` Christoph Lameter
2012-02-29 15:24 ` Christoph Lameter
2012-03-01 7:30 ` Namhyung Kim [this message]
2012-03-01 7:30 ` Namhyung Kim
2012-03-01 15:03 ` Christoph Lameter
2012-03-01 15:03 ` Christoph Lameter
2012-03-02 7:12 ` Namhyung Kim
2012-03-02 7:12 ` Namhyung Kim
2012-03-02 16:13 ` Christoph Lameter
2012-03-02 16:13 ` Christoph Lameter
2012-03-04 10:34 ` Minchan Kim
2012-03-04 10:34 ` Minchan Kim
2012-03-05 8:42 ` Namhyung Kim
2012-03-05 8:42 ` Namhyung Kim
2012-03-05 10:59 ` Minchan Kim
2012-03-05 10:59 ` Minchan Kim
2012-03-05 14:48 ` Christoph Lameter
2012-03-05 14:48 ` Christoph Lameter
2012-03-06 1:16 ` Minchan Kim
2012-03-06 1:16 ` Minchan Kim
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