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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/11/2026 9:16 PM, David Hildenbrand (Arm) wrote: > 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) Sure, will add this in the next posting. [...] >> +++ 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? > Yes, Will do. >> + >> 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" ? > Yes, will do. This is more clean. Thanks, Shivank