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From: Shakeel Butt To: Joanne Koong Cc: David Hildenbrand , SeongJae Park , miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, bernd.schubert@fastmail.fm, kernel-team@meta.com Subject: Re: [PATCH v4 4/6] mm/memory-hotplug: add finite retries in offline_pages() if migration fails Message-ID: <2ecmqokellladmioa5rvw57lqbz3ouevx5q5weyydjius3cu2s@vl3siu2b3gs6> References: <20241108173309.71619-1-sj@kernel.org> <04020bb7-5567-4b91-a424-62c46f136e2a@redhat.com> <4d2062bd-3cf3-4488-8dfc-b0aa672ee786@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 145B1C000A X-Stat-Signature: dfkq9ubzpr1f7wt8oy4c69escoegufmu X-Rspam-User: X-HE-Tag: 1731104163-411343 X-HE-Meta: U2FsdGVkX19YhPSLQAf5swMMyxdBObDCJefC6sMjqsGiqbuT7Y1lJ1+MQ+qXGvVIBT/iu8suF+k6m941rZ0pCklv9/DtnzxlCacyjaxlrKpfzUoWmSA5M4CPWTPQQoZfMwGz5rcildU1i7bn1RKLzmUNNF+6oBX3TDJ+7VQqBSO9welTSRkYsr+7dK1/59L3FlClYOQBzA1ZN0LTiBU2PGkOV6LJ72pDjrDm6I//IbShp6gI4oC3axjxVD8KWozWwVFwLfIqyc8uv8tGF5ipcUMHyjC2lddvYF0JIYXY21enP2HVOmYMy5bevaEd4eibuh7N+ZT1DBo6IAYE/WWGwNTVWAaa78jo7d9ugSOpNiGWZhRe6jIxcBM2Nx3kyWx2/BKCuEJfjvb2CYX2o5oHO5AaOx3qGUSNvF9klNc87NqN+gFCJ44pJgDDJzR+vzLUPvEfwftyFfcOVVvjA3IIlKNlA8FP05pxWOfFTazrSN62Cs2yCoQa4p2oPiKsyljg8G/TzsO8Fa9OoPMOK0DqzZLPHFikqKOMt6r93IYEqCKzS/lyeFcfn3kXpR3naLWKmXsMou7i4NiikBH0PjpcOuNTnBbECKNdHQb4tVbrUa6UAe1pZi0nAGp/DyESgvX6hiE0FE530Nuo9wOVta6WCblXU+NfLmSsml42gR3PzwT8zGiZT3U0QY4vGqYZOVsjw2qm7x0wGSeMpDhRN09t3wwB6pWs0BUy/bN8AFh/vzxXBujFp0+dJbVls3cU9IHDVWHmiPIMVyb2ViSzG3+/k8QYbfBUCUYh8u9SK18EhZXh76Q4dY6rjMzNSpcDTFLQctJfPn0t28kVqExUFIRxGO6Jo721nWzaQSokF46pUYxMvlWljwCON/mRifxRO4OSP9eXgMkx9X6MldUlJRc7IWUBb+8CTl31k3zmdxakSvJ9gm1+OyW/P+2xtAXSLMECdP1LDNtSzjbUBCs2IaT TxV3WsiI WqhuT+3hINq6XmHoXrhtR/5FJxWW1zgSAGCzDX0KANe3sFtlZj9TI2gL2GxON+Iini85oF2THKq3HyrvivmADi8i2G1IWz4zzesrSrXzO6Lhkf1gZz2dQ0wAcrbl9bfV2iovAYo4Ih3/5zi9nJxXiEbl2NtIyJMhcTan0avWRVI16Er0tVo4fttVtYF/lOSZAI266Q6eeIE1GwYjPJJMY3PIgoU1yAqbYswCQC3ouj9qXfMLkaVRrXahFp86XSA0AzmGzFYS17dj3Qn8U5e5G631kMhi1GeNLkstY 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 Fri, Nov 08, 2024 at 01:42:15PM -0800, Joanne Koong wrote: > On Fri, Nov 8, 2024 at 1:27 PM Shakeel Butt wrote: > > > > On Fri, Nov 08, 2024 at 08:00:25PM +0100, David Hildenbrand wrote: > > > On 08.11.24 19:56, David Hildenbrand wrote: > > > > On 08.11.24 18:33, SeongJae Park wrote: > > > > > + David Hildenbrand > > > > > > > > > > On Thu, 7 Nov 2024 15:56:12 -0800 Joanne Koong wrote: > > > > > > > > > > > In offline_pages(), do_migrate_range() may potentially retry forever if > > > > > > the migration fails. Add a return value for do_migrate_range(), and > > > > > > allow offline_page() to try migrating pages 5 times before erroring > > > > > > out, similar to how migration failures in __alloc_contig_migrate_range() > > > > > > is handled. > > > > > > > > > > I'm curious if this could cause unexpected behavioral differences to memory > > > > > hotplugging users, and how '5' is chosen. Could you please enlighten me? > > > > > > > > > > > > > I'm wondering how much more often I'll have to nack such a patch. :) > > > > > > A more recent discussion: https://lore.kernel.org/linux-mm/52161997-15aa-4093-a573-3bfd8da14ff1@fujitsu.com/T/#mdda39b2956a11c46f8da8796f9612ac007edbdab > > > > > > Long story short: this is expected and documented > > > > Thanks David for the background. > > > > Joanne, simply drop this patch. It is not required for your series. > > Awesome, I'm happy to drop this patch. > > Just curious though - don't we need this in order to mitigate the > scenario where if an unprivileged fuse server never completes > writeback, we don't run into this infinite loop? Or is it that memory > hotplugging is always initiated from userspace so if it does run into > an infinite loop (like also in that thread David linked), userspace is > responsible for sending a signal to terminate it? I think irrespective of the source of the hotplug, the current behavior of infinite retries in some cases is documented and kind of expected, so no need to fix it. (Though I don't know all the source of hotplug.)