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b=I9Jd5nfZWYnAAIWkm5HtQ41vtn2X45+QnXvjTYfZ712ObRMdSmxGFfCesA+4JOlm1 cC0u7ZPHAxYlA5LuSH9cuJmMpOxJxp1Wx1+tW3CxsTnzw8ntiXntwwgVtroS152JtP knfcQ9x/RL97zasSs7R+JZxmE0it9X/eiJp8LW1/EqJl7IBvM/uVHyB5uj7ZHUpeNK AnWw9ANRmaBo2M/YHJc5hoEZRA48jwd3tY98B0YruB01EhZddZQK2KhAAzcHLvEPMu BKlkMRkq6pKa+bUSGtbYLQduocH5Bq8y8pbCvH9jkLMUfjn2rRPXDww2TZE80P+q3P RanO510TC6Lsg== Message-ID: <27f6f5d6-e81b-4e0a-af39-b175187299e2@kernel.org> Date: Mon, 8 Jun 2026 17:25:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/7] mm/migrate: add batch-copy path in migrate_pages_batch To: "Garg, Shivank" , 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 References: <20260428155043.39251-2-shivankg@amd.com> <20260428155043.39251-10-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: rspam07 X-Rspam-User: X-Stat-Signature: umh9iigsca1kkx6bk5zft54a6t4ghgmf X-Rspamd-Queue-Id: E821B20003 X-HE-Tag: 1780932343-549464 X-HE-Meta: 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 RkSzOOmu 2AH8iEi0T3yV+RKrCafiTT4Mp8r9dIyOcEtd8FCik+jm0LZbeH+lm17o84bAwybkY+YOTnhY3ri/hr0VmR4lXmqeduvs4fTGq5um5aIhz7g4WC/MFqiYs62Z2JJJavQfm2LdNfUNrvhX1oceKlWLE6NsbA2aO7AqqhMnuA504T9oOq2z7oGVDPb1uyLjru6QcNcfP2N+6ldso7LK+ESVudfrJSiVrVDA8TT+IY5kkYfA4aCkmuz+bFXOiUFsDntSX58o2cLT5bcuAcUB+5BV9NmpY2tFHf7y94Z9bc7SWl3HzD0biZbP/ivj+cOaR9X1DaKuaopa2AE2VhhHCgzumAdjDP5Y28v7DotIRqthGA74Mvg5w1esUh873oodVSMYxIVR4VUtJCDaqvXUeCeKyYkrt2Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/20/26 17:06, Garg, Shivank wrote: > > > On 5/11/2026 9:10 PM, David Hildenbrand (Arm) wrote: >> On 4/28/26 17:50, Shivank Garg wrote: >>> Add folios_mc_copy() which walks list of src and dst folios in lockstep, >>> and copies folio content via folio_mc_copy(). folios_cnt parameter is >>> unused here, but is part of the offload_copy callback signature used by >>> later patches in the series. >>> >>> Split unmapped folios into batch-eligible (unmap_batch/dst_batch) and >>> standard (unmap_single/dst_single) lists, gated by the >>> migrate_offload_enabled which is off by default. So, when no offload >>> driver is active, the branch is never taken and everything goes >>> through the standard path. >>> >>> After TLB flush, batch copy the eligible folios via folios_mc_copy() >>> and pass already_copied=true into migrate_folios_move() so >>> __migrate_folio() skips the per-folio copy. >>> >>> On batch copy failure, already_copied flag stays false and each folio >>> fall back to individual copy. >>> >>> Signed-off-by: Shivank Garg >>> --- >>> include/linux/mm.h | 2 ++ >>> mm/migrate.c | 61 +++++++++++++++++++++++++++++++++++----------- >>> mm/util.c | 30 +++++++++++++++++++++++ >>> 3 files changed, 79 insertions(+), 14 deletions(-) >> >> [...] >> >>> >>> +DEFINE_STATIC_KEY_FALSE(migrate_offload_enabled); >>> + >>> static const struct movable_operations *offline_movable_ops; >>> static const struct movable_operations *zsmalloc_movable_ops; >>> >>> @@ -1724,6 +1727,12 @@ static int migrate_hugetlbs(struct list_head *from, new_folio_t get_new_folio, >>> return nr_failed; >>> } >>> >>> +/* movable_ops folios have their own migrate path */ >>> +static bool folio_supports_batch_copy(struct folio *folio) >>> +{ >>> + return likely(!page_has_movable_ops(&folio->page)); >>> +} >> >> As these things are not actually folios (and callers will have to be taught to >> distinguish them way, way earlier), I guess you should make this >> >> /* movable_ops pages have a separate migration path */ >> static bool page_supports_batch_copy(struct page *page) >> ... > > I'll change this. > >> >>> + >>> static void migrate_folios_move(struct list_head *src_folios, >>> struct list_head *dst_folios, >>> free_folio_t put_new_folio, unsigned long private, >>> @@ -1752,7 +1761,7 @@ static void migrate_folios_move(struct list_head *src_folios, >>> /* >>> * The rules are: >>> * 0: folio will be freed >>> - * -EAGAIN: stay on the unmap_folios list >>> + * -EAGAIN: stay on the src_folios list >>> * Other errno: put on ret_folios list >>> */ >>> switch (rc) { >> >> >> [...] >> >>> --- a/mm/util.c >>> +++ b/mm/util.c >>> @@ -778,6 +778,36 @@ int folio_mc_copy(struct folio *dst, struct folio *src) >>> } >>> EXPORT_SYMBOL(folio_mc_copy); >>> >>> +/** >>> + * folios_mc_copy - Copy the contents of list of folios. >>> + * @dst_list: destination folio list. >>> + * @src_list: source folio list. >>> + * @folios_cnt: unused here, present for callback signature compatibility. >>> + * >>> + * Walks list of src and dst folios in lockstep and copies folio >>> + * content via folio_mc_copy(). The caller must ensure both lists have >>> + * the same number of entries. This may sleep. >> >> This *function* >> > > Will add function. > >>> + * >>> + * Return: 0 on success, negative errno on failure. >>> + */ >>> +int folios_mc_copy(struct list_head *dst_list, struct list_head *src_list, >>> + unsigned int __always_unused folios_cnt) >>> +{ >>> + struct folio *src, *dst; >>> + int ret; >>> + >>> + dst = list_first_entry(dst_list, struct folio, lru); >>> + list_for_each_entry(src, src_list, lru) { >>> + ret = folio_mc_copy(dst, src); >>> + if (ret) >>> + return ret; >>> + dst = list_next_entry(dst, lru); >>> + } >> >> Wouldn't it be cleaner to remember "already copied" immediately after we ... >> performed the copy? (succeeded with folio_mc_copy) > > IIUC, you mean something like: > list_for_each_entry(src, src_list, lru) { > ret = folio_mc_copy(dst, src); > if (ret) > return ret; > dst->migrate_info |= FOLIO_CONTENT_COPIED; > dst = list_next_entry(dst, lru); > } > > This will be cleaner. However, it will make the folios_mc_copy() specific for > page migration and can't be reused by other potential callers. > And offload driver (like DCBM) must set the already copied marker > themselves for successful copies. Right, maybe some helper for that would be possible? > This will have an upside that on partial-success (even a single failed copy), > it will no longer forces re-copy of the whole batch. > If that's the intention, I'll move this to migrate.c itself. True. I'd probably have to take a look at the end result to see if it looks better that way. -- Cheers, David