From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
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>
Subject: Re: [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone
Date: Fri, 11 Dec 2020 16:09:02 -0500 [thread overview]
Message-ID: <CA+CK2bC6u4wnHX53ZhfPtQBLTDbD3t4V9Zuhj=HwD3gEyL4Puw@mail.gmail.com> (raw)
In-Reply-To: <20201211204600.GD5487@ziepe.ca>
On Fri, Dec 11, 2020 at 3:46 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Fri, Dec 11, 2020 at 03:40:57PM -0500, Pavel Tatashin wrote:
> > On Fri, Dec 11, 2020 at 3:23 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > >
> > > On Fri, Dec 11, 2020 at 03:21:39PM -0500, Pavel Tatashin wrote:
> > > > @@ -1593,7 +1592,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
> > > > }
> > > >
> > > > if (!isolate_lru_page(head)) {
> > > > - list_add_tail(&head->lru, &cma_page_list);
> > > > + list_add_tail(&head->lru, &movable_page_list);
> > > > mod_node_page_state(page_pgdat(head),
> > > > NR_ISOLATED_ANON +
> > > > page_is_file_lru(head),
> > > > @@ -1605,7 +1604,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
> > > > i += step;
> > > > }
> > > >
> > > > - if (!list_empty(&cma_page_list)) {
> > > > + if (!list_empty(&movable_page_list)) {
> > >
> > > You didn't answer my earlier question, is it OK that ZONE_MOVABLE
> > > pages leak out here if ioslate_lru_page() fails but the
> > > moval_page_list is empty?
> > >
> > > I think the answer is no, right?
> > In my opinion it is OK. We are doing our best to not pin movable
> > pages, but if isolate_lru_page() fails because pages are currently
> > locked by someone else, we will end up long-term pinning them.
> > See comment in this patch:
> > + * 1. Pinned pages: (long-term) pinning of movable pages is avoided
> > + * when pages are pinned and faulted, but it is still possible that
> > + * address space already has pages in ZONE_MOVABLE at the time when
> > + * pages are pinned (i.e. user has touches that memory before
> > + * pinning). In such case we try to migrate them to a different zone,
> > + * but if migration fails the pages can still end-up pinned in
> > + * ZONE_MOVABLE. In such case, memory offlining might retry a long
> > + * time and will only succeed once user application unpins pages.
>
> It is not "retry a long time" it is "might never complete" because
> userspace will hold the DMA pin indefinitely.
>
> Confused what the point of all this is then ??
>
> I thought to goal here is to make memory unplug reliable, if you leave
> a hole like this then any hostile userspace can block it forever.
You are right, I used a wording from the previous comment, and it
should be made clear that pin may be forever. Without these patches it
is guaranteed that hot-remove will fail if there are pinned pages as
ZONE_MOVABLE is actually the first to be searched. Now, it will fail
only due to exceptions listed in ZONE_MOVABLE comment:
1. pin + migration/isolation failure
2. memblock allocation due to limited amount of space for kernelcore
3. memory holes
4. hwpoison
5. Unmovable PG_offline pages (? need to study why this is a scenario).
Do you think we should unconditionally unpin pages, and return error
when isolation/migration fails?
Pasha
>
> Jason
next prev parent reply other threads:[~2020-12-11 21:58 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-11 20:21 [PATCH v3 0/6] prohibit pinning pages in ZONE_MOVABLE Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 1/6] mm/gup: don't pin migrated cma pages in movable zone Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 2/6] mm cma: rename PF_MEMALLOC_NOCMA to PF_MEMALLOC_PIN Pavel Tatashin
2020-12-14 14:03 ` Michal Hocko
2020-12-15 4:37 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 3/6] mm: apply per-task gfp constraints in fast path Pavel Tatashin
2020-12-14 14:09 ` Michal Hocko
2020-12-15 5:20 ` Pavel Tatashin
2020-12-15 8:25 ` Michal Hocko
2020-12-15 17:35 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 4/6] mm: honor PF_MEMALLOC_PIN for all movable pages Pavel Tatashin
2020-12-14 14:17 ` Michal Hocko
2020-12-15 5:24 ` Pavel Tatashin
2020-12-15 8:27 ` Michal Hocko
2020-12-15 17:28 ` Pavel Tatashin
2020-12-11 20:21 ` [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone Pavel Tatashin
2020-12-11 20:23 ` Jason Gunthorpe
2020-12-11 20:40 ` Pavel Tatashin
2020-12-11 20:46 ` Jason Gunthorpe
2020-12-11 21:09 ` Pavel Tatashin [this message]
2020-12-11 21:29 ` David Hildenbrand
2020-12-11 21:35 ` Pavel Tatashin
2020-12-11 21:53 ` David Hildenbrand
2020-12-11 23:00 ` Pavel Tatashin
2020-12-12 0:07 ` John Hubbard
2020-12-11 23:50 ` Jason Gunthorpe
2020-12-12 7:29 ` David Hildenbrand
2020-12-14 13:36 ` Jason Gunthorpe
2020-12-14 14:21 ` David Hildenbrand
2020-12-14 14:30 ` Michal Hocko
2020-12-14 14:19 ` Michal Hocko
2020-12-11 20:21 ` [PATCH v3 6/6] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning Pavel Tatashin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CA+CK2bC6u4wnHX53ZhfPtQBLTDbD3t4V9Zuhj=HwD3gEyL4Puw@mail.gmail.com' \
--to=pasha.tatashin@soleen.com \
--cc=akpm@linux-foundation.org \
--cc=dan.j.williams@intel.com \
--cc=david@redhat.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=jgg@ziepe.ca \
--cc=jhubbard@nvidia.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mhocko@suse.com \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=osalvador@suse.de \
--cc=peterz@infradead.org \
--cc=rientjes@google.com \
--cc=rostedt@goodmis.org \
--cc=sashal@kernel.org \
--cc=tyhicks@linux.microsoft.com \
--cc=vbabka@suse.cz \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).