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imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=JELj8aOD; spf=pass (imf11.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778514371; a=rsa-sha256; cv=none; b=adKR+chrAlaLCeheAHjJnbMDXEwICstG/cKs2M4vxUW9VByBu7/ZGMXembaERX4eqFIkU8 o4VOq+h1gazc/l0VhnmgsekTJ7l+zwn6bG5pGaYpoX8wFApG/AsQp9JIfhMAYX5NgypH0M t6Efv2+xC8YnwoYf7BqY+UPmNUXeCsc= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id DA95D60103; Mon, 11 May 2026 15:46:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81BF4C2BCB0; Mon, 11 May 2026 15:46:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778514370; bh=q74dAch6WvCTTrmanvn0QGUN5w0P2uuTvOSqDfVMl5c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JELj8aODuyGTtzXYd8ycVD5vBvKzt3EPIXfY0/rjidrOKBjc5aSUlZ0An2ne2SQPw Z6SlvdQFRR9ACsykOp90aM8eGrO3IEAbw/7ITQo1A6LcqSw4feGqhpcMdiSPh5+rL9 aKng0uxk0jymU1lTRB4ApJFRtoAGE/b3UrUylDIJyXczIyuxFFrq+OopMi8+idsGaH A0yfbWRiQHGD2Y3f5za980yqfqd5BVRulkQ+elL/Ej7EmH91hZthshQjW/zCKiT1Tp KfEb2P1yuQfLAb7LDDU2qFIzHD2RTJgFHnphDiC9Mliv50ISV1hxm+0cBR/pHBrlNK /obqFPMLBpm7w== Message-ID: <5a0ee441-3c0d-43b0-84f3-7e727ae042bd@kernel.org> Date: Mon, 11 May 2026 17:46:00 +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; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260428155043.39251-12-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: qufouxi5w385zpmz1c96ummp6of3gcsx X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 881A44000C X-Rspam-User: X-HE-Tag: 1778514371-968107 X-HE-Meta: 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 gWKizOuh cqaPmXegnSbaoFqt2JhQV7mfkBHhDFxtO4+PRPR8OLQVhHUDn7A4ephZBWy4giN8JpVAgah6p5q55VMes7ZtUShZOdzI3c1G7Ve4eLei+2X8aqtq/4rs/7JRNRmf6WBvXO4doqmT0mhM9tALD4wKltJ2fAUVIujo76KNF2dp5vYw8Abr7v4rtyryF+NL/6LeL86SLqNapO2BUjvAuKYwnCasG3OHtWY3Lx0t62lXNthgXbMJznMuNth8tsBPJC65Nm9Bq/HnNgW5n9kwLAvDA4bk4yq5582SA4XVNTy5iuGF8NTwQyRP5hWvX1JLZEEF4IcXWk/IfXxk4VPPTLDD/DNltpx72Ue5du/KQ 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 MAINTAINERS file deserves some love (likely put the new files under the migration section) > --- > 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; > + } > +} > + > +static int migrate_offload_batch_copy(struct list_head *dst_batch, > + struct list_head *src_batch, > + unsigned int nr_batch) > +{ > + int idx, rc; > + > + idx = srcu_read_lock(&migrate_offload_srcu); > + rc = static_call(migrate_offload_copy)(dst_batch, src_batch, nr_batch); > + srcu_read_unlock(&migrate_offload_srcu, idx); > + return rc; > +} > +#else > +static bool migrate_offload_do_batch(int reason) > +{ > + return false; > +} > + > +static int migrate_offload_batch_copy(struct list_head *dst_batch, > + struct list_head *src_batch, > + unsigned int nr_batch) > +{ > + return -EOPNOTSUPP; > +} > +#endif Can't all that go to migrate_copy_offload.(hc) Looks like a clean interface form migrate.c, no? > + > static const struct movable_operations *offline_movable_ops; > static const struct movable_operations *zsmalloc_movable_ops; > > @@ -1833,7 +1880,7 @@ static int migrate_pages_batch(struct list_head *from, > struct folio *folio, *folio2, *dst = NULL; > int rc, rc_saved = 0, nr_pages; > unsigned int nr_batch = 0; > - bool batch_copied = false; > + bool do_batch = false, batch_copied = false; > LIST_HEAD(unmap_batch); > LIST_HEAD(dst_batch); > LIST_HEAD(unmap_single); > @@ -1843,6 +1890,8 @@ static int migrate_pages_batch(struct list_head *from, > VM_WARN_ON_ONCE(mode != MIGRATE_ASYNC && > !list_empty(from) && !list_is_singular(from)); > > + do_batch = migrate_offload_do_batch(reason); > + > for (pass = 0; pass < nr_pass && retry; pass++) { > retry = 0; > thp_retry = 0; > @@ -1984,8 +2033,7 @@ static int migrate_pages_batch(struct list_head *from, > nr_retry_pages += nr_pages; > break; > case 0: > - if (static_branch_unlikely(&migrate_offload_enabled) && > - folio_supports_batch_copy(folio)) { > + if (do_batch && folio_supports_batch_copy(folio)) { I was about to say, the migrate_offload_enabled usage in the previous patch looks off. Can you move that to this patch here, and use in the previous patch simply a default migrate_offload_do_batch() that simply returns "false" ? > list_move_tail(&folio->lru, &unmap_batch); > list_add_tail(&dst->lru, &dst_batch); > nr_batch++; > @@ -2017,7 +2065,8 @@ static int migrate_pages_batch(struct list_head *from, > > /* Batch-copy eligible folios before the move phase */ > if (!list_empty(&unmap_batch)) { > - rc = folios_mc_copy(&dst_batch, &unmap_batch, nr_batch); > + rc = migrate_offload_batch_copy(&dst_batch, &unmap_batch, > + nr_batch); > batch_copied = (rc == 0); > } > > diff --git a/mm/migrate_copy_offload.c b/mm/migrate_copy_offload.c -- Cheers, David