From: Hugh Dickins <hughd@google.com>
To: Zi Yan <ziy@nvidia.com>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <ak@linux.intel.com>, Christoph Lameter <cl@linux.com>,
Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Yang Shi <shy828301@gmail.com>,
Sidhartha Kumar <sidhartha.kumar@oracle.com>,
Vishal Moola <vishal.moola@gmail.com>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
"Huang, Ying" <ying.huang@intel.com>,
Nhat Pham <nphamcs@gmail.com>,
Yosry Ahmed <yosryahmed@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma
Date: Mon, 23 Oct 2023 14:10:38 -0700 (PDT) [thread overview]
Message-ID: <8c933f5b-983e-a332-e410-6ee6872f839f@google.com> (raw)
In-Reply-To: <61FB8BFF-E3CB-4C99-8A6D-845A69E4E76F@nvidia.com>
On Mon, 23 Oct 2023, Zi Yan wrote:
> On 19 Oct 2023, at 16:39, Hugh Dickins wrote:
> > @@ -1170,6 +1170,15 @@ static struct folio *new_folio(struct folio *src, unsigned long start)
> > break;
> > }
> >
> > + /*
> > + * __get_vma_policy() now expects a genuine non-NULL vma. Return NULL
> > + * when the page can no longer be located in a vma: that is not ideal
> > + * (migrate_pages() will give up early, presuming ENOMEM), but good
> > + * enough to avoid a crash by syzkaller or concurrent holepunch.
> > + */
> > + if (!vma)
> > + return NULL;
> > +
>
> How often would this happen? I just want to point out that ENOMEM can cause
> src THPs or large folios to be split by migrate_pages().
The only case I know of it happening was when a file was mapped, then that
file truncated (cutting out the source page) before migrate_pages(&pagelist)
reached it - rather a syzbotty thing to do, not of great reallife concern.
I won't assert that's the only way: I've a ghost of a memory of another way,
that I can't quite resurface, from a long-ago version of queue_pages_range().
But in the end just didn't care enough about it, because this is really just
to save a bisection point from crashing - the possibility goes away in the
11/12 commit which follows this one, which takes VMA out of it altogether.
Hugh
next prev parent reply other threads:[~2023-10-23 21:10 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-03 9:12 [PATCH v2 00/12] mempolicy: cleanups leading to NUMA mpol without vma Hugh Dickins
2023-10-03 9:15 ` [PATCH v2 01/12] hugetlbfs: drop shared NUMA mempolicy pretence Hugh Dickins
2023-10-03 9:16 ` [PATCH v2 02/12] kernfs: drop shared NUMA mempolicy hooks Hugh Dickins
2023-10-03 9:17 ` [PATCH v2 03/12] mempolicy: fix migrate_pages(2) syscall return nr_failed Hugh Dickins
2023-10-07 7:27 ` Huang, Ying
2023-10-03 9:19 ` [PATCH v2 04/12] mempolicy trivia: delete those ancient pr_debug()s Hugh Dickins
2023-10-03 9:20 ` [PATCH v2 05/12] mempolicy trivia: slightly more consistent naming Hugh Dickins
2023-10-03 9:21 ` [PATCH v2 06/12] mempolicy trivia: use pgoff_t in shared mempolicy tree Hugh Dickins
2023-10-03 9:22 ` [PATCH v2 07/12] mempolicy: mpol_shared_policy_init() without pseudo-vma Hugh Dickins
2023-10-03 9:24 ` [PATCH v2 08/12] mempolicy: remove confusing MPOL_MF_LAZY dead code Hugh Dickins
2023-10-03 22:28 ` Yang Shi
2023-10-03 9:25 ` [PATCH v2 09/12] mm: add page_rmappable_folio() wrapper Hugh Dickins
2023-10-03 9:26 ` [PATCH v2 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma Hugh Dickins
2023-10-19 20:39 ` [PATCH v3 " Hugh Dickins
2023-10-23 16:53 ` domenico cerasuolo
2023-10-23 17:53 ` Andrew Morton
2023-10-23 18:10 ` domenico cerasuolo
2023-10-23 19:05 ` Johannes Weiner
2023-10-23 19:48 ` Hugh Dickins
2023-10-24 6:44 ` [PATCH] mempolicy: alloc_pages_mpol() for NUMA policy without vma: fix Hugh Dickins
2023-10-24 8:17 ` kernel test robot
2023-10-24 15:56 ` Hugh Dickins
2023-10-24 16:09 ` [PATCH v2] " Hugh Dickins
2023-10-23 18:34 ` [PATCH v3 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma Zi Yan
2023-10-23 21:10 ` Hugh Dickins [this message]
2023-10-23 21:13 ` Zi Yan
2023-10-03 9:27 ` [PATCH v2 11/12] mempolicy: mmap_lock is not needed while migrating folios Hugh Dickins
2023-10-03 9:29 ` [PATCH v2 12/12] mempolicy: migration attempt to match interleave nodes Hugh Dickins
2023-10-24 6:50 ` [PATCH] mempolicy: migration attempt to match interleave nodes: fix Hugh Dickins
2023-10-24 15:18 ` Liam R. Howlett
2023-10-24 16:32 ` Hugh Dickins
2023-10-24 16:45 ` Matthew Wilcox
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