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bh=rjBnCv2ULxEz7oJV432ZaM8iYHq42FRu53Pj0zGrV9M=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=zs96Isk7BUDkozaK8NVXBH8wpXf+B/3rxNacG3e2KJ/ICcJ4eE1nxsieBaCKjgUML Y1dTApNqBhpNN/PZOLM/fPeU/20Ejpve2zmzemg8+je873WcrwrJQ25yNlGBjUDTfF zeM38a4vfl9ja8eUzf2FWQm7oVeU42BOLKkErqsI= Date: Sat, 25 Feb 2023 20:55:43 -0800 From: Andrew Morton To: Huang Ying Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , "Xu, Pengfei" , Christoph Hellwig , Stefan Roesch , Tejun Heo , Xin Hao , Zi Yan , Yang Shi , Baolin Wang , Matthew Wilcox , Mike Kravetz Subject: Re: [PATCH 0/3] migrate_pages: fix deadlock in batched synchronous migration Message-Id: <20230225205543.5d56714d2145ac45da25369e@linux-foundation.org> In-Reply-To: <20230224141145.96814-1-ying.huang@intel.com> References: <20230224141145.96814-1-ying.huang@intel.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 30C7AC000E X-Stat-Signature: 3n33bgqt8zmykcaq9qb96cthx15fchpk X-HE-Tag: 1677387346-26583 X-HE-Meta: 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 rzpHVI5a 2gOVkbj7nF8fTXvkXMWbCz2CowSXfs+xVpn39uAHmbQHFk8IJF7OwC69Ir4AjAtN+5cgnCkSXyLFAHFBLRxb201AxcF9/WSR+folU2ZhLL6/3OQp8AbT24mImXT1vVb0wxpe6Sl5AzzBNvuNm8aIkO9Xqd89aP40yIRIk6tK3r/61NCJSE6jX6HS9ztQHVPMsAon/qS1I1LGYkLIzroPTjCmJ1Ju0pZ6GV7XbxKIyrtxnE9JmikU7WVB9DwqjjNO32F7h56IQUZvlCAa+BA7eAWk52w0OQ01KuL5xu1TBt6VmUIzi2ya5Q/KAusY4//7ZTIYFtxwoHFNnI4fyOWzlW+Pz8i/QefEV/f5KUhXXsn+JbBWvbXd5xqtZ6YvISdw/kDS52X5r6o1fqDRFTL7AULX93awoeG3VOW8q 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: On Fri, 24 Feb 2023 22:11:42 +0800 Huang Ying wrote: > Two deadlock bugs were reported for the migrate_pages() batching > series. "migrate_pages(): batch TLB flushing" > Thanks Hugh and Pengfei. Analysis shows that if we have > locked some other folios except the one we are migrating, it's not > safe in general to wait synchronously, for example, to wait the > writeback to complete or wait to lock the buffer head. > > So 1/3 fixes the deadlock in a simple way, where the batching support > for the synchronous migration is disabled. The change is > straightforward and easy to be understood. While 3/3 re-introduce the > batching for synchronous migration via trying to migrate > asynchronously in batch optimistically, then fall back to migrate > synchronously one by one for fail-to-migrate folios. Test shows that > this can restore the TLB flushing batching performance for synchronous > migration effectively. If anyone backports the "migrate_pages(): batch TLB flushing" series into their kernels, they will want to know about such fixes. So we can help them by providing suitable Link: tags. Such a Link: may also be helpful to people who are performing git bisection searches for some issue but who keep stumbling over the issues which this series addresses. Being lazy, I slapped Fixes: 6f7d760e86fa ("migrate_pages: move THP/hugetlb migration support check to simplify code") on all three, as this was the final patch in that series. Inaccurate, but it means that these fixes will land in a suitable place if anyone needs them.