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b=mBxJJpc0a/J/qXlh4wWG3qDWE4ieZbnSHK+x9tW8qtkWjOssiwWJ1tVKEaohonphl lUqG7s0u0H/KQQ7W0QoEMIiYFR0CLUrbIYz/SzS2YGiASQvW55Gi+p59TyCM1V13h8 14JsNDOW2uejTxYxVX0MNhn1s44gU6rzn7LMylITcHvdXdPDl7IOwAzcnTbPpHgqjF +LA6wvaSpkuik4y3XSNPIbQPZdc1Kbdtum9w5HMihvlnT1ppt5GDA89L10T+aPWBOm E+rO5UO5l8FCBrdjHSl8cCiejQw/I0Ai247DRAG3r6xckRxmvBjEqBUVUWwIUvlBNf YY5vAiqWgJWWw== Message-ID: Date: Mon, 23 Mar 2026 13:20:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 2/6] mm/migrate: skip data copy for already-copied folios To: "Garg, Shivank" , akpm@linux-foundation.org Cc: lorenzo.stoakes@oracle.com, 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, weixugc@google.com, dan.j.williams@intel.com, 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, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260309120725.308854-3-shivankg@amd.com> <20260309120725.308854-8-shivankg@amd.com> <4bfec2c1-9747-49d2-a490-87ab204cec1c@kernel.org> <99d3a0be-d33e-47c8-88b4-3f0e21f4a1cf@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: rspam02 X-Rspamd-Queue-Id: DC071A000B X-Stat-Signature: 5sax18zo1oe59nrggpexd9o7nc5bybu8 X-Rspam-User: X-HE-Tag: 1774268418-938959 X-HE-Meta: U2FsdGVkX192AF01C8OCwbcvddYa4USijvRLdAL4HxFy5P7W4aiMa+u250NaJSCfaDijB7FM/lgMpmW0UKpCua8ACMskg1H70TdB8WGG9hohzvJl/IVWZy4QBUrz3mZXhRl7pjrTvVGSDQQEg5DlcwQ8um+yw5yDIeASZ8GeBaVnzfpHRFZW0QOKinVI6VOgnG6YdeQI+da33+aAecFRcaddsQJqWRqvL3JglX6oAkNzwBhRHK5AS0Sf4s7ufYEBfl5qlC/BbTiwYddzFSx4RsQOE9ESxD6YyVVExaQCBGKB2zzHY+bCy1hE76O31yhxpNnLRfp5iqty1RUUcC7QbX+sVgQuqI2fUZfYffgTZHyo8/gog/zlZQOlZOumbwezgGd3Hsfr0zOo8M/FkDATrjEK7jgsyO8ouSvzc8ZZ8oD3VnuUuJg7yxjOwO3WmmgsKJfzWt3c34DN2HwB/kLZl8HHb12Djjz0MF+Ti7EyD1ZfK3xlQRAKDUek4dMgT41RTd95qwM+zI/bgaBeVBWO9q9UT3FM1L4UJ4l6CpteUZGT3ndZffia6A+mHC6+jmco6Ng5Tx+OqWv0Ay09ddcVLjaF/LclR0kduu5h+Rhub+g67TyBwh1pGF1Gjq6RBILRHLYanw61rm4CRh2j/8NiSnfr9xoe/q+es1o+q9paEUipo+86Ezdo5Fyp6wimevNvUeX99cv0+olnRCwMc1UI3Xf0zmduA1LMbA2k8/un0Y3LlDCY4HkruPTgrr2a5FUSXdVYuOBJ2W11+8ZnwefkNb9Zw3316cbMsUJErTG6LU7AJk/rVMG6xiQXOF8LWZkjYMPDPYbtVALowWoXCtAh4ueONPC9nIm0d3vW3uoRIU4yzVs9ZLRNLj/TYSOyE3KcKTm8WHGkRNqcsF17ki/d2A1RVxOfH4Xqa+7/mjjNH9B5BSPmhymIqM4AA8PSWBZOeIEJlgNJH4fRCF+QnYG hsCOWifJ AcXUCL1+bpJ7DdxxPAfEBzBSSCF+9I/1p5y81HFFlEmzwscGwaPN1VFwwGRaTBUfCc/1+r4ukgHPOdqnCQiaQ2RU0gk/9PqzbqVEOddIL+OiiJYC3RMxABRzCYDOswq5nM5tAV35T5vpQfc1hMsW3LqhRShlmKuKJdQjTNMnrLMyb4GLxQRYzDT2p3rBA0UTgADt3QWLZjSsUwHlowm6xj3WVn39TI8VbQkdPHnGD2gq7nDsY3XH5uVGFUAvfLlaA1pvBn/O+orgSO5pxXUfYw7LqgBqZ4dGTF6PZbUVN9ayNRG2Cv+xURzPksuoB+ZDM76ql93WEIe2Hz0YStPo475VE374hr6F1apcC Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/15/26 19:25, Garg, Shivank wrote: > > > On 3/12/2026 3:14 PM, David Hildenbrand (Arm) wrote: >> On 3/9/26 13:07, Shivank Garg wrote: >>> Add a PAGE_ALREADY_COPIED flag to the dst->private 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 in a later patch. >>> >>> Move the dst->private state enum earlier in the file so >>> __migrate_folio() and move_to_new_folio() can see PAGE_ALREADY_COPIED. >>> >>> Signed-off-by: Shivank Garg >>> --- >>> mm/migrate.c | 52 +++++++++++++++++++++++++++++++--------------------- >>> 1 file changed, 31 insertions(+), 21 deletions(-) >>> >>> diff --git a/mm/migrate.c b/mm/migrate.c >>> index 1bf2cf8c44dd..1d8c1fb627c9 100644 >>> --- a/mm/migrate.c >>> +++ b/mm/migrate.c >>> @@ -848,6 +848,18 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) >>> } >>> EXPORT_SYMBOL(folio_migrate_flags); >>> >>> +/* >>> + * To record some information during migration, we use unused private >>> + * field of struct folio of the newly allocated destination folio. >>> + * This is safe because nobody is using it except us. >>> + */ >>> +enum { >>> + PAGE_WAS_MAPPED = BIT(0), >>> + PAGE_WAS_MLOCKED = BIT(1), >>> + PAGE_ALREADY_COPIED = BIT(2), >>> + PAGE_OLD_STATES = PAGE_WAS_MAPPED | PAGE_WAS_MLOCKED | PAGE_ALREADY_COPIED, >> >> All these states really only apply to proper folios (not movable_ops). >> So once we complete decoupling movable_ops migration from folio >> migration, these flags would only appear in the folio migration part. >> >> Can we convert them first to state it clearly already that these are >> folio migration flags? >> >> FOLIO_MF_WAS_MAPPED >> >> ... >> > Sure, done. > > Should I fold it into the series? Or send it as independent patch as this series would > likely take few more rounds of reviews and discussion. Best to send it out as a standalone cleanup :) -- Cheers, David