From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 33B154014B4 for ; Mon, 11 May 2026 15:35:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778513750; cv=none; b=jE2H7khhD8GO9QwuBUI2Mj8YHL4x2DwQHJmla4zqkarB9inGWz8kY45+7eU+NsPthhzyBX++gY5cJcKe9qj8qcMIs43iwdLChXighRZMytkJIAoieMlFzdBiN9LoF+RIBjBw7CsyOgzdCeLgK3OUa7EOzR2DOsrZHOj9glC/ul8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778513750; c=relaxed/simple; bh=Kkv8LGne/ZB9kLOhAmHhVPrjWXuFNdHyoMZUMle6Dao=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rYVsZQW6dVziwWowrF5lcfPoOGC3pzGQwzyqDZB40JJHZ/LI5Ce/rvj/u7RvvUzqvD3wmgTVO+YduVJPu7Z8coFUXlBQBEDIuSp+xIzcrTBo5D9A4X9Ey/nT6t+yexcTzva3gbH84hzNzTtYceGqdGOwf5mhOd+yQ0myjzm5Ybc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UrVzk3xF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UrVzk3xF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8514EC2BCB0; Mon, 11 May 2026 15:35:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778513749; bh=Kkv8LGne/ZB9kLOhAmHhVPrjWXuFNdHyoMZUMle6Dao=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=UrVzk3xFELKUlkQ/hhUlbzbhTvDTcAfpEhLVJM9Jd+DaO2z71QCog6q2Q7Ul2vX3A m7LILd1ByNtzzGSiBStB2CRi6UJC8wRau9+S0DBGlcJWDxE1s2bpO/wnSEpoyXUQnm 6Fd48gW9YlQ5kYhmYXGoJOkd4YT6mtEAQJ6JqBxktVCz+2X32yLM9R9LEiHb4w0N27 S8awfLRdjfpOJG4xUctMF8MoU4n9oZ9C9HlO16m7/s6xiasT3xvu/Nr4HBWJWa/h8q i8q0Qhx1w3XWxPBlhAjCLXI5OSOmFX+QXtyoS9QMdLrg/57Mzmp+sTeb6C6db34s/e 0FMWo1scqtbKw== Message-ID: <810e9a58-9c08-4f5e-af5f-866685ca09b2@kernel.org> Date: Mon, 11 May 2026 17:35:39 +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 3/7] mm/migrate: skip data copy for already-copied folios 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 References: <20260428155043.39251-2-shivankg@amd.com> <20260428155043.39251-8-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: <20260428155043.39251-8-shivankg@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/28/26 17:50, Shivank Garg wrote: > Add a FOLIO_ALREADY_COPIED flag to the dst->migrate_info migration > state. When set, __migrate_folio() skips folio_mc_copy() and > performs metadata-only migration. All callers currently pass > already_copied=false. The batch-copy path enables it later in a > subsequent patch. > > Move the dst->migrate_info state enum earlier in the file so > __migrate_folio() and move_to_new_folio() can see FOLIO_ALREADY_COPIED. > > Signed-off-by: Shivank Garg > --- > mm/migrate.c | 53 +++++++++++++++++++++++++++++++--------------------- > 1 file changed, 32 insertions(+), 21 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 03c2a6f7e5e4..c493e67e359d 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -850,6 +850,19 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) > } > EXPORT_SYMBOL(folio_migrate_flags); > > +/* > + * To record some information during migration, we use the migrate_info > + * field of struct folio of the newly allocated destination folio. > + * This is safe because nobody is using it except us. > + */ > +enum { > + FOLIO_WAS_MAPPED = BIT(0), > + FOLIO_WAS_MLOCKED = BIT(1), > + FOLIO_ALREADY_COPIED = BIT(2), I wonder whether we want to talk about "folio content copied", to not confuse it with folio flags copied etc. FOLIO_CONTENT_COPIED. Thoughts? > + FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED | > + FOLIO_ALREADY_COPIED, > +}; > + > /************************************************************ > * Migration functions > ***********************************************************/ > @@ -859,14 +872,20 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst, > enum migrate_mode mode) > { > int rc, expected_count = folio_expected_ref_count(src) + 1; > + bool already_copied = (dst->migrate_info & FOLIO_ALREADY_COPIED); const, and no need for (). > + > + if (already_copied) > + dst->migrate_info = 0; Hm, why is that required? Might deserve a comment. Likely you want to clear the "already copied" marker? dst->migrate_info &= ~FOLIO_ALREADY_COPIED; ? But I wonder if this really belongs exactly here. > > /* Check whether src does not have extra refs before we do more work */ > if (folio_ref_count(src) != expected_count) > return -EAGAIN; > > - rc = folio_mc_copy(dst, src); > - if (unlikely(rc)) > - return rc; > + if (!already_copied) { > + rc = folio_mc_copy(dst, src); > + if (unlikely(rc)) > + return rc; > + } > > rc = __folio_migrate_mapping(mapping, dst, src, expected_count); > if (rc) > @@ -1090,7 +1109,7 @@ static int fallback_migrate_folio(struct address_space *mapping, > * 0 - success > */ > static int move_to_new_folio(struct folio *dst, struct folio *src, > - enum migrate_mode mode) > + enum migrate_mode mode, bool already_copied) > { > struct address_space *mapping = folio_mapping(src); > int rc = -EAGAIN; > @@ -1098,6 +1117,9 @@ static int move_to_new_folio(struct folio *dst, struct folio *src, > VM_BUG_ON_FOLIO(!folio_test_locked(src), src); > VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst); > > + if (already_copied) > + dst->migrate_info = FOLIO_ALREADY_COPIED; |= ? > + > if (!mapping) > rc = migrate_folio(mapping, dst, src, mode); > else if (mapping_inaccessible(mapping)) > @@ -1129,17 +1151,6 @@ static int move_to_new_folio(struct folio *dst, struct folio *src, > return rc; > } > > -/* > - * To record some information during migration, we use the migrate_info > - * field of struct folio of the newly allocated destination folio. > - * This is safe because nobody is using it except us. > - */ > -enum { > - FOLIO_WAS_MAPPED = BIT(0), > - FOLIO_WAS_MLOCKED = BIT(1), > - FOLIO_OLD_STATES = FOLIO_WAS_MAPPED | FOLIO_WAS_MLOCKED, > -}; > - > static void __migrate_folio_record(struct folio *dst, > int old_folio_state, struct anon_vma *anon_vma) > { > @@ -1353,7 +1364,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, > static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private, > struct folio *src, struct folio *dst, > enum migrate_mode mode, enum migrate_reason reason, > - struct list_head *ret) > + struct list_head *ret, bool already_copied) > { > int rc; > int old_folio_state = 0; > @@ -1379,7 +1390,7 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private, > src_partially_mapped = folio_test_partially_mapped(src); > } > > - rc = move_to_new_folio(dst, src, mode); > + rc = move_to_new_folio(dst, src, mode, already_copied); > if (rc) > goto out; > > @@ -1536,7 +1547,7 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, > } > > if (!folio_mapped(src)) > - rc = move_to_new_folio(dst, src, mode); > + rc = move_to_new_folio(dst, src, mode, false); ... mode, /* already_copied = */ false > > if (page_was_mapped) > remove_migration_ptes(src, !rc ? dst : src, ttu); > @@ -1720,7 +1731,7 @@ static void migrate_folios_move(struct list_head *src_folios, > struct list_head *ret_folios, > struct migrate_pages_stats *stats, > int *retry, int *thp_retry, int *nr_failed, > - int *nr_retry_pages) > + int *nr_retry_pages, bool already_copied) > { > struct folio *folio, *folio2, *dst, *dst2; > bool is_thp; > @@ -1737,7 +1748,7 @@ static void migrate_folios_move(struct list_head *src_folios, > > rc = migrate_folio_move(put_new_folio, private, > folio, dst, mode, > - reason, ret_folios); > + reason, ret_folios, already_copied); > /* > * The rules are: > * 0: folio will be freed > @@ -1994,7 +2005,7 @@ static int migrate_pages_batch(struct list_head *from, > migrate_folios_move(&unmap_folios, &dst_folios, > put_new_folio, private, mode, reason, > ret_folios, stats, &retry, &thp_retry, > - &nr_failed, &nr_retry_pages); > + &nr_failed, &nr_retry_pages, false); > } dito. -- Cheers, David