From: Andrew Morton <akpm@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: mbligh@aracnet.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, kmannth@us.ibm.com
Subject: Re: [Bugme-new] [Bug 2019] New: Bug from the mm subsystem involving X (fwd)
Date: Wed, 4 Feb 2004 16:56:20 -0800 [thread overview]
Message-ID: <20040204165620.3d608798.akpm@osdl.org> (raw)
In-Reply-To: <Pine.LNX.4.58.0402041639420.2086@home.osdl.org>
Linus Torvalds <torvalds@osdl.org> wrote:
>
>
>
> On Wed, 4 Feb 2004, Martin J. Bligh wrote:
> >
> > Oh hell ... I remember what's wrong with this whole bit. pfn_valid is
> > used inconsistently in different places, IIRC. Linus / Andrew ... what
> > do you actually want it to mean? Some things seem to use it to say
> > "the memory here is valid accessible RAM", some things "there is a
> > valid struct page for this pfn". I was aiming for the latter, but a
> > few other arches seemed to disagree.
> >
> > Could I get a ruling on this? ;-)
>
> It _definitely_ means "there is a valid 'struct page' for this pfn".
>
> To test for "there is RAM" here, you need to first check that the pfn is
> valid, and then you can check what the page type is (usually that would be
> PageReserved(), but it could be a highmem check or something like that
> too).
pfn_valid() could become quite expensive indeed, and it lies on super-duper
hotpaths.
An alternative which is less conceptually clean but should work in this
case is to mark all vma's which were created by /dev/mem mappings as VM_IO,
and test that in remap_page_range().
The marking of mmap_mem() vma's as VM_IO has been in -mm for four months.
But I didn't changelog it at the time and I've forgotten why I wrote it
(really). It's something to do with get_user_pages() against a mapping of
/dev/mem :(
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.2-rc3/2.6.2-rc3-mm1/broken-out/get_user_pages-handle-VM_IO.patch
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: mbligh@aracnet.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, kmannth@us.ibm.com
Subject: Re: [Bugme-new] [Bug 2019] New: Bug from the mm subsystem involving X (fwd)
Date: Wed, 4 Feb 2004 16:56:20 -0800 [thread overview]
Message-ID: <20040204165620.3d608798.akpm@osdl.org> (raw)
In-Reply-To: <Pine.LNX.4.58.0402041639420.2086@home.osdl.org>
Linus Torvalds <torvalds@osdl.org> wrote:
>
>
>
> On Wed, 4 Feb 2004, Martin J. Bligh wrote:
> >
> > Oh hell ... I remember what's wrong with this whole bit. pfn_valid is
> > used inconsistently in different places, IIRC. Linus / Andrew ... what
> > do you actually want it to mean? Some things seem to use it to say
> > "the memory here is valid accessible RAM", some things "there is a
> > valid struct page for this pfn". I was aiming for the latter, but a
> > few other arches seemed to disagree.
> >
> > Could I get a ruling on this? ;-)
>
> It _definitely_ means "there is a valid 'struct page' for this pfn".
>
> To test for "there is RAM" here, you need to first check that the pfn is
> valid, and then you can check what the page type is (usually that would be
> PageReserved(), but it could be a highmem check or something like that
> too).
pfn_valid() could become quite expensive indeed, and it lies on super-duper
hotpaths.
An alternative which is less conceptually clean but should work in this
case is to mark all vma's which were created by /dev/mem mappings as VM_IO,
and test that in remap_page_range().
The marking of mmap_mem() vma's as VM_IO has been in -mm for four months.
But I didn't changelog it at the time and I've forgotten why I wrote it
(really). It's something to do with get_user_pages() against a mapping of
/dev/mem :(
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.2-rc3/2.6.2-rc3-mm1/broken-out/get_user_pages-handle-VM_IO.patch
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next prev parent reply other threads:[~2004-02-05 1:04 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-04 23:17 [Bugme-new] [Bug 2019] New: Bug from the mm subsystem involving X (fwd) Martin J. Bligh
2004-02-04 23:17 ` Martin J. Bligh
2004-02-04 23:58 ` Linus Torvalds
2004-02-04 23:58 ` Linus Torvalds
2004-02-05 0:12 ` Martin J. Bligh
2004-02-05 0:12 ` Martin J. Bligh
2004-02-05 0:36 ` Martin J. Bligh
2004-02-05 0:36 ` Martin J. Bligh
2004-02-05 0:43 ` Linus Torvalds
2004-02-05 0:43 ` Linus Torvalds
2004-02-05 0:56 ` Andrew Morton [this message]
2004-02-05 0:56 ` Andrew Morton
2004-02-05 1:29 ` Linus Torvalds
2004-02-05 1:29 ` Linus Torvalds
2004-02-05 1:56 ` Keith Mannthey
2004-02-05 1:56 ` Keith Mannthey
2004-02-05 2:04 ` Linus Torvalds
2004-02-05 2:04 ` Linus Torvalds
2004-02-05 2:33 ` Keith Mannthey
2004-02-05 2:33 ` Keith Mannthey
2004-02-05 2:47 ` Linus Torvalds
2004-02-05 2:47 ` Linus Torvalds
2004-02-06 7:17 ` Martin J. Bligh
2004-02-06 7:17 ` Martin J. Bligh
2004-02-06 7:19 ` Martin J. Bligh
2004-02-06 7:19 ` Martin J. Bligh
2004-02-06 9:57 ` Dave Hansen
2004-02-06 9:57 ` Dave Hansen
2004-02-06 15:49 ` Martin J. Bligh
2004-02-06 15:49 ` Martin J. Bligh
2004-02-06 17:22 ` Dave Hansen
2004-02-06 17:22 ` Dave Hansen
2004-02-06 19:59 ` Martin J. Bligh
2004-02-06 19:59 ` Martin J. Bligh
2004-02-06 20:16 ` Linus Torvalds
2004-02-06 20:16 ` Linus Torvalds
2004-02-06 21:18 ` Martin J. Bligh
2004-02-06 21:18 ` Martin J. Bligh
[not found] <51080000.1075936626@flay.suse.lists.linux.kernel>
[not found] ` <Pine.LNX.4.58.0402041539470.2086@home.osdl.org.suse.lists.linux.kernel>
[not found] ` <60330000.1075939958@flay.suse.lists.linux.kernel>
[not found] ` <64260000.1075941399@flay.suse.lists.linux.kernel>
[not found] ` <Pine.LNX.4.58.0402041639420.2086@home.osdl.org.suse.lists.linux.kernel>
[not found] ` <20040204165620.3d608798.akpm@osdl.org.suse.lists.linux.kernel>
[not found] ` <Pine.LNX.4.58.0402041719300.2086@home.osdl.org.suse.lists.linux.kernel>
[not found] ` <1075946211.13163.18962.camel@dyn318004bld.beaverton.ibm.com.suse.lists.linux.kernel>
[not found] ` <Pine.LNX.4.58.0402041800320.2086@home.osdl.org.suse.lists.linux.kernel>
[not found] ` <98220000.1076051821@[10.10.2.4].suse.lists.linux.kernel>
[not found] ` <1076061476.27855.1144.camel@nighthawk.suse.lists.linux.kernel>
[not found] ` <5450000.1076082574@[10.10.2.4].suse.lists.linux.kernel>
[not found] ` <1076088169.29478.2928.camel@nighthawk.suse.lists.linux.kernel>
[not found] ` <218650000.1076097590@flay.suse.lists.linux.kernel>
[not found] ` <Pine.LNX.4.58.0402061215030.30672@home.osdl.org.suse.lists.linux.kernel>
[not found] ` <220850000.1076102320@flay.suse.lists.linux.kernel>
2004-02-07 3:54 ` Andi Kleen
2004-02-07 4:49 ` Martin J. Bligh
2004-02-07 5:21 ` Andi Kleen
2004-02-07 6:37 ` Nick Piggin
2004-02-07 7:31 ` Martin J. Bligh
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