From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 643703D5676 for ; Mon, 8 Jun 2026 15:25:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780932344; cv=none; b=Vv/AimZ7ssKSRLT7pnVV/Cag0xTgocU1R0M9DywYCh6on/9M2wVrp7jMETVh+dkR7oze+yT+lNo0Vgd+trqYqR1wCG6yfR+rjVU2ddP8uKodm7vryyni1yrdZqvwspaAmU8wgb4+mQS9dyqYgqPqovNM0S6UXNWjnloRgK3x4+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780932344; c=relaxed/simple; bh=GwTsgPSpbU6jRAf/JGF0T79kPLKVIGklh9NjaJBkH4o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=U8FwaUKzwaj1qlLBavkd1DzIy0MEfN2NuWWucDLCX1uExd4EGxMXqAPSTEqcfZ19GSTd6s4k0MoNN7u96I71YutEqv2fB2KeaDXQFLBc8c8ezAH0rqNLdllOtWbDJxXTQ+eRopz/XFEUCb4iE1u5gMqKvmDzRqossSV5egpuFLk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I9Jd5nfZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="I9Jd5nfZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E6111F00893; Mon, 8 Jun 2026 15:25:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780932343; bh=DmENGgQRwxMmo42f5vCP8Aa9knmtXvGq5kfEhKqCwHg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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