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b=e2eK+wQoKuU/dStkO+lg6+gtbsaLruL0IGzpDs4HYazxL3WOgrg8jWQDkYzrqWIRj Le5W454VCVDQa3xKJhEB5TAALlzvBVxVh+FCrI7GccrHB9JFd0iA+Y47iaZ35pZCtc yQDKifj7fpN5kve7KYUNMrLsfHY5CAwn4qNSX/OiQWn65N2YN7U0sVhCh3guBz7UkQ gm1wjLuiZhhOu/tjoLb4xsyed0Q4gh8gO7FHChhJC6uN5QC2Z7bjCOEUVIX9MEU9t8 Q/GuM9sJ5PRO8qkV/8MxIw4ybiB0+w5pbq4YPsGqtceMZAgmPzx3NuYTX8V02lbjhU yjB2uC5SLTpUA== Message-ID: <9145ae5b-a33e-4092-8cb5-efa18ae61287@kernel.org> Date: Mon, 11 May 2026 17:50:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/7] mm/migrate: add copy offload registration infrastructure To: Shivank Garg , akpm@linux-foundation.org Cc: kinseyho@google.com, weixugc@google.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, willy@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, dave@stgolabs.net, Jonathan.Cameron@huawei.com, rkodsara@amd.com, vkoul@kernel.org, bharata@amd.com, sj@kernel.org, rientjes@google.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, dave.hansen@intel.com, hannes@cmpxchg.org, jhubbard@nvidia.com, peterx@redhat.com, riel@surriel.com, shakeel.butt@linux.dev, stalexan@redhat.com, tj@kernel.org, nifan.cxl@gmail.com, jic23@kernel.org, aneesh.kumar@kernel.org, nathan.lynch@amd.com, Frank.li@nxp.com, djbw@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mike Day References: <20260428155043.39251-2-shivankg@amd.com> <20260428155043.39251-12-shivankg@amd.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8EEE080007 X-Rspam-User: X-Stat-Signature: gicaqp1ngpemxj8qjgbsbrpkp4h9gz77 X-HE-Tag: 1778514628-371153 X-HE-Meta: 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 lQZhGy/S m8BRTqQEqYatJX8TpF4SlIDHHHWAiGqg1iSDJzA81Ur/u8MKJSejb8AkVExpdbzmFr0xHhMVR5rmJT6TCjoqI/qODIYpZ01zkihEnpi4f29szL/bU5qi1RjQo+6bRXm1KiRkU2onl6fqpTP83ZUGGeMZEo4J4q7reYuEYXP1hrNGObvWHQr78bmzquNDl9DsAXxbJiueUQjQCmU2+KP/Ni1dLdfKjgcvU4eqgjEukWI72UzJHOIzglD4lu6iRub45Ygszeigpt7J4jAWVCyLlcBOqAhkAulyrQn8aye0CBzbUV/gU45PW1CiJmwHk/izP5hFmvffTfl24kEA5kRY4W4FzOdtaKU4z/pGC Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/28/26 17:50, Shivank Garg wrote: > Add a registration interface that lets a single offload provider > (DMA, multi-threaded CPU copy, etc) take over the batch folio copy > performed by migrate_pages_batch(). > > The provider fills in a struct migrator with an offload_copy() > callback and calls migrate_offload_register(). Registration patches > the migrate_offload_copy() static_call and flips the > migrate_offload_enabled static branch. The migrate_offload_unregister() > reverts both. > > Whether a migration reason is batch-copy eligible is decided by the > core in migrate_offload_do_batch(). A migrator may decline a particular > batch (e.g. when nr_batch is too small to amortize setup) by returning > -EOPNOTSUPP, and the move phase falls back to per-folio CPU copy. > > Only one migrator can be active at a time. A second registration > returns -EBUSY, and only the active migrator can unregister itself. > The static_call dispatch is protected by SRCU so that the > synchronize_srcu() in unregister waits for all in-flight copy before > the module reference is dropped. > > Co-developed-by: Mike Day > Signed-off-by: Mike Day > Signed-off-by: Shivank Garg > --- > include/linux/migrate_copy_offload.h | 44 +++++++++++++ > mm/Kconfig | 6 ++ > mm/Makefile | 1 + > mm/migrate.c | 57 +++++++++++++++-- > mm/migrate_copy_offload.c | 94 ++++++++++++++++++++++++++++ > 5 files changed, 198 insertions(+), 4 deletions(-) > create mode 100644 include/linux/migrate_copy_offload.h > create mode 100644 mm/migrate_copy_offload.c > > diff --git a/include/linux/migrate_copy_offload.h b/include/linux/migrate_copy_offload.h > new file mode 100644 > index 000000000000..d68b10a84743 > --- /dev/null > +++ b/include/linux/migrate_copy_offload.h > @@ -0,0 +1,44 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _LINUX_MIGRATE_COPY_OFFLOAD_H > +#define _LINUX_MIGRATE_COPY_OFFLOAD_H > + > +#include > +#include > +#include > +#include > + > +struct list_head; > +struct module; > + > +#define MIGRATOR_NAME_LEN 32 > + > +/** > + * struct migrator - batch-copy provider for page migration. > + * @name: name of the provider. > + * @offload_copy: copy @folio_cnt folios from @src_list to @dst_list. > + * > + * The migrator may inspect @folio_cnt to decide whether the batch > + * is worth offloading, e.g. skip when the batch is too small to > + * amortize setup cost. If returns error, the core falls back to CPU copy. > + * > + * @owner: module providing the migrator. > + */ > +struct migrator { > + char name[MIGRATOR_NAME_LEN]; > + int (*offload_copy)(struct list_head *dst_list, > + struct list_head *src_list, > + unsigned int folio_cnt); > + struct module *owner; > +}; > + > +#ifdef CONFIG_MIGRATION_COPY_OFFLOAD > +extern struct static_key_false migrate_offload_enabled; > +extern struct srcu_struct migrate_offload_srcu; > +int migrate_offload_register(struct migrator *m); > +int migrate_offload_unregister(struct migrator *m); > +#else > +static inline int migrate_offload_register(struct migrator *m) { return -EOPNOTSUPP; } > +static inline int migrate_offload_unregister(struct migrator *m) { return -EOPNOTSUPP; } > +#endif > + > +#endif /* _LINUX_MIGRATE_COPY_OFFLOAD_H */ > diff --git a/mm/Kconfig b/mm/Kconfig > index e8bf1e9e6ad9..325d79619680 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -647,6 +647,12 @@ config MIGRATION > config DEVICE_MIGRATION > def_bool MIGRATION && ZONE_DEVICE > > +# Page-migration batch-copy offload infrastructure. > +# Selected by migrator drivers (e.g. CONFIG_DCBM_DMA). > +config MIGRATION_COPY_OFFLOAD > + bool > + depends on MIGRATION > + > config ARCH_ENABLE_HUGEPAGE_MIGRATION > bool > > diff --git a/mm/Makefile b/mm/Makefile > index 8ad2ab08244e..db1ac8097089 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -96,6 +96,7 @@ obj-$(CONFIG_FAILSLAB) += failslab.o > obj-$(CONFIG_FAIL_PAGE_ALLOC) += fail_page_alloc.o > obj-$(CONFIG_MEMTEST) += memtest.o > obj-$(CONFIG_MIGRATION) += migrate.o > +obj-$(CONFIG_MIGRATION_COPY_OFFLOAD) += migrate_copy_offload.o > obj-$(CONFIG_NUMA) += memory-tiers.o > obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o > obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o > diff --git a/mm/migrate.c b/mm/migrate.c > index 6c2f1cb66f96..9af070f9a1f2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -44,6 +44,8 @@ > #include > #include > #include > +#include > +#include > > #include > > @@ -54,6 +56,51 @@ > > DEFINE_STATIC_KEY_FALSE(migrate_offload_enabled); > > +#ifdef CONFIG_MIGRATION_COPY_OFFLOAD > +DEFINE_SRCU(migrate_offload_srcu); > +DEFINE_STATIC_CALL(migrate_offload_copy, folios_mc_copy); > + > +static bool migrate_offload_do_batch(int reason) > +{ > + if (!static_branch_unlikely(&migrate_offload_enabled)) > + return false; > + > + switch (reason) { > + case MR_COMPACTION: > + case MR_SYSCALL: > + case MR_DEMOTION: > + case MR_NUMA_MISPLACED: > + return true; > + default: > + return false; What's the exact reason we don't do this for hotunplug etc? IOW, why do we make this depend on a reason? -- Cheers, David