linux-kernel - Re: [PATCH v1 1/2] mm/migrate: remove MIGRATEPAGE

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Message-ID: <B4A54756-87EC-4795-855C-3F80114456FF@nvidia.com>
Date: Mon, 11 Aug 2025 14:13:21 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linuxppc-dev@...ts.ozlabs.org, virtualization@...ts.linux.dev,
 linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
 linux-btrfs@...r.kernel.org, jfs-discussion@...ts.sourceforge.net,
 Andrew Morton <akpm@...ux-foundation.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
 Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Benjamin LaHaise <bcrl@...ck.org>, Chris Mason <clm@...com>,
 Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
 Muchun Song <muchun.song@...ux.dev>, Oscar Salvador <osalvador@...e.de>,
 Dave Kleikamp <shaggy@...nel.org>, Matthew Brost <matthew.brost@...el.com>,
 Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
 Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Alistair Popple <apopple@...dia.com>, Minchan Kim <minchan@...nel.org>,
 Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v1 1/2] mm/migrate: remove MIGRATEPAGE_UNMAP

On 11 Aug 2025, at 10:39, David Hildenbrand wrote:

> migrate_folio_unmap() is the only user of MIGRATEPAGE_UNMAP. We want to
> remove MIGRATEPAGE_* completely.
>
> It's rather weird to have a generic MIGRATEPAGE_UNMAP, documented to be
> returned from address-space callbacks, when it's only used for an
> internal helper.
>
> Let's start by having only a single "success" return value for
> migrate_folio_unmap() -- 0 -- by moving the "folio was already freed"
> check into the single caller.
>
> There is a remaining comment for PG_isolated, which we renamed to
> PG_movable_ops_isolated recently and forgot to update.
>
> While we might still run into that case with zsmalloc, it's something we
> want to get rid of soon. So let's just focus that optimization on real
> folios only for now by excluding movable_ops pages. Note that concurrent
> freeing can happen at any time and this "already freed" check is not
> relevant for correctness.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  include/linux/migrate.h |  1 -
>  mm/migrate.c            | 40 ++++++++++++++++++++--------------------
>  2 files changed, 20 insertions(+), 21 deletions(-)
>
LGTM. Reviewed-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi