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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 16-20020a250910000000b00d749bc5b169sm2962754ybj.43.2023.10.23.14.10.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Oct 2023 14:10:52 -0700 (PDT) Date: Mon, 23 Oct 2023 14:10:38 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Zi Yan cc: Hugh Dickins , Andrew Morton , Andi Kleen , Christoph Lameter , Matthew Wilcox , Mike Kravetz , David Hildenbrand , Suren Baghdasaryan , Yang Shi , Sidhartha Kumar , Vishal Moola , Kefeng Wang , Greg Kroah-Hartman , Tejun Heo , Mel Gorman , Michal Hocko , "Huang, Ying" , Nhat Pham , Yosry Ahmed , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma In-Reply-To: <61FB8BFF-E3CB-4C99-8A6D-845A69E4E76F@nvidia.com> Message-ID: <8c933f5b-983e-a332-e410-6ee6872f839f@google.com> References: <74e34633-6060-f5e3-aee-7040d43f2e93@google.com> <1738368e-bac0-fd11-ed7f-b87142a939fe@google.com> <61FB8BFF-E3CB-4C99-8A6D-845A69E4E76F@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 0B714180017 X-Rspam-User: X-Stat-Signature: uttsuqca4z7768jb6ksn3a8mh4wmgybr X-Rspamd-Server: rspam03 X-HE-Tag: 1698095453-387297 X-HE-Meta: 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 Ul4dUflH hDJJp8Ka4EMzyjihHsJD4ke+eyCINNTgKyXyp8DQAP2XOl2fXi7E0i91IojiXnso9f8dVulOGoQjB5HyamT2Ayr0TvE4a0VsFEJc0T6FTyFPAKBnucVjZWfJFeOuQQWguPZrVorPN7XaVcRfNjjXFp+aULNzbapjX5KhpGMn+vg+qEl+ZGpOTHX6RU5gmUE91pxLlyUmENr5tNwSBx1YZ5rxUMNVNdvAUrda/iV8twW92WPj86iN3n/5Y8OaUyffCWiTuMQOK2tM/2ej6yZoXxKuJ1ZgUnRcDbox/XXmSlFvJS+okReXlAscGXJTEb66Vp6NzNLoc3xZo19M3HB1CUmTJQxVdDhAoKXgKCcdVj21KD5Q/HMO1cmvGk8RhaBu5naTB+nlAw/hDzTPZZOZvDfojRfRW5cpFHpZUC6w31miNkbyx/QoL+R1iIpDISRQtFdGf5DGTuBlFoueyN9y1gRwqzotnj+UeISYH X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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