From: Jason Gunthorpe <jgg@ziepe.ca>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>, Michal Hocko <mhocko@suse.com>,
David Hildenbrand <david@redhat.com>,
Oscar Salvador <osalvador@suse.de>,
Dan Williams <dan.j.williams@intel.com>,
Sasha Levin <sashal@kernel.org>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
mike.kravetz@oracle.com, Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@suse.de>,
Matthew Wilcox <willy@infradead.org>,
David Rientjes <rientjes@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
Ira Weiny <ira.weiny@intel.com>,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v5 08/14] mm/gup: do not allow zero page for pinned pages
Date: Tue, 19 Jan 2021 14:47:51 -0400 [thread overview]
Message-ID: <20210119184751.GD4605@ziepe.ca> (raw)
In-Reply-To: <CA+CK2bBKbht34Hkg9YvhwYAiAjd3NMd_+Eir9wfx+07V-Y2TTA@mail.gmail.com>
On Tue, Jan 19, 2021 at 01:34:26PM -0500, Pavel Tatashin wrote:
> On Tue, Jan 19, 2021 at 1:30 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Mon, Jan 18, 2021 at 11:39:14PM -0500, Pavel Tatashin wrote:
> > > Zero page should not be used for long term pinned pages. Once pages
> > > are pinned their physical addresses cannot changed until they are unpinned.
> > >
> > > Guarantee to always return real pages when they are pinned by adding
> > > FOLL_WRITE.
> > >
> > > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > > mm/gup.c | 10 +++++++++-
> > > 1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > No, this will definitely break things
>
> What will break
Things assuming GUP doesn't break COW, making all GUP WRITE was
already tried and revered for some other reason
> > Why does the zero page have to be movable?
>
> It is not even about being movable, we can't cow pinned pages returned
> by GUP call, how can we use zero page for that?
The zero page is always zero, it is never written to. What does cow
matter?
Jason
next prev parent reply other threads:[~2021-01-19 18:47 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 4:39 [PATCH v5 00/14] prohibit pinning pages in ZONE_MOVABLE Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 01/14] mm/gup: don't pin migrated cma pages in movable zone Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 02/14] mm/gup: check every subpage of a compound page during isolation Pavel Tatashin
2021-01-19 18:05 ` Jason Gunthorpe
2021-01-19 4:39 ` [PATCH v5 03/14] mm/gup: return an error on migration failure Pavel Tatashin
2021-01-19 18:28 ` Jason Gunthorpe
2021-01-19 4:39 ` [PATCH v5 04/14] mm/gup: check for isolation errors Pavel Tatashin
2021-01-19 18:22 ` Jason Gunthorpe
2021-01-19 18:27 ` Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 05/14] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_PIN Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 06/14] mm: apply per-task gfp constraints in fast path Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 07/14] mm: honor PF_MEMALLOC_PIN for all movable pages Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 08/14] mm/gup: do not allow zero page for pinned pages Pavel Tatashin
2021-01-19 18:30 ` Jason Gunthorpe
2021-01-19 18:34 ` Pavel Tatashin
2021-01-19 18:47 ` Jason Gunthorpe [this message]
2021-01-19 20:14 ` Pavel Tatashin
2021-01-19 20:48 ` Pavel Tatashin
2021-01-19 23:35 ` Jason Gunthorpe
2021-01-19 4:39 ` [PATCH v5 09/14] mm/gup: migrate pinned pages out of movable zone Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 10/14] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 11/14] mm/gup: change index type to long as it counts pages Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 12/14] mm/gup: longterm pin migration cleaup Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 13/14] selftests/vm: test flag is broken Pavel Tatashin
2021-01-19 4:39 ` [PATCH v5 14/14] selftests/vm: test faulting in kernel, and verify pinnable pages Pavel Tatashin
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