linux-kernel - Re: [PATCH v1 21/29] mm: rename PG_isolated to PG_movable_ops

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Message-ID: <443de491-4ade-45f3-9c9b-b4428b0f0aaa@lucifer.local>
Date: Tue, 1 Jul 2025 13:51:51 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
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        Jonathan Corbet <corbet@....net>,
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        Alexander Viro <viro@...iv.linux.org.uk>,
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        Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH v1 21/29] mm: rename PG_isolated to
 PG_movable_ops_isolated

On Mon, Jun 30, 2025 at 03:00:02PM +0200, David Hildenbrand wrote:
> Let's rename the flag to make it clearer where it applies (not folios
> ...).
>
> While at it, define the flag only with CONFIG_MIGRATION.
>
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  include/linux/page-flags.h | 16 +++++++++++-----
>  mm/compaction.c            |  2 +-
>  mm/migrate.c               | 14 +++++++-------
>  3 files changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 016a6e6fa428a..aa48b05536bca 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -167,10 +167,9 @@ enum pageflags {
>  	/* Remapped by swiotlb-xen. */
>  	PG_xen_remapped = PG_owner_priv_1,
>
> -	/* non-lru isolated movable page */

Ah nice to drop another confusing reference to LRU when really meaning
'non-could-be-lru-possibly' :P

> -	PG_isolated = PG_reclaim,
> -
>  #ifdef CONFIG_MIGRATION
> +	/* movable_ops page that is isolated for migration */
> +	PG_movable_ops_isolated = PG_reclaim,
>  	/* this is a movable_ops page (for selected typed pages only) */
>  	PG_movable_ops = PG_uptodate,
>  #endif
> @@ -1126,8 +1125,6 @@ static inline bool folio_contain_hwpoisoned_page(struct folio *folio)
>
>  bool is_free_buddy_page(const struct page *page);
>
> -PAGEFLAG(Isolated, isolated, PF_ANY);
> -
>  #ifdef CONFIG_MIGRATION
>  /*
>   * This page is migratable through movable_ops (for selected typed pages
> @@ -1146,8 +1143,17 @@ PAGEFLAG(Isolated, isolated, PF_ANY);
>   * page_has_movable_ops() instead.
>   */
>  PAGEFLAG(MovableOps, movable_ops, PF_NO_TAIL);
> +/*
> + * A movable_ops page has this flag set while it is isolated for migration.
> + * This flag primarily protects against concurrent migration attempts.
> + *
> + * Once migration ended (success or failure), the flag is cleared. The
> + * flag is managed by the migration core.
> + */
> +PAGEFLAG(MovableOpsIsolated, movable_ops_isolated, PF_NO_TAIL);
>  #else
>  PAGEFLAG_FALSE(MovableOps, movable_ops);
> +PAGEFLAG_FALSE(MovableOpsIsolated, movable_ops_isolated);
>  #endif

Nit, but maybe worth sticking /* CONFIG_MIGRATION */ on else and endif? Not a
huge block so maybe not massively important but just a thought!

>
>  /**
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 349f4ea0ec3e5..bf021b31c7ece 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1051,7 +1051,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>  		if (!PageLRU(page)) {
>  			/* Isolation code will deal with any races. */
>  			if (unlikely(page_has_movable_ops(page)) &&
> -					!PageIsolated(page)) {
> +			    !PageMovableOpsIsolated(page)) {
>  				if (locked) {
>  					unlock_page_lruvec_irqrestore(locked, flags);
>  					locked = NULL;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c6c9998014ec8..62a3ee590b245 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -135,7 +135,7 @@ bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
>  		goto out_putfolio;
>
>  	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> -	if (PageIsolated(page))
> +	if (PageMovableOpsIsolated(page))
>  		goto out_no_isolated;
>
>  	mops = page_movable_ops(page);
> @@ -146,8 +146,8 @@ bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
>  		goto out_no_isolated;
>
>  	/* Driver shouldn't use the isolated flag */
> -	VM_WARN_ON_ONCE_PAGE(PageIsolated(page), page);
> -	SetPageIsolated(page);
> +	VM_WARN_ON_ONCE_PAGE(PageMovableOpsIsolated(page), page);
> +	SetPageMovableOpsIsolated(page);
>  	folio_unlock(folio);
>
>  	return true;
> @@ -177,10 +177,10 @@ static void putback_movable_ops_page(struct page *page)
>  	struct folio *folio = page_folio(page);
>
>  	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> -	VM_WARN_ON_ONCE_PAGE(!PageIsolated(page), page);
> +	VM_WARN_ON_ONCE_PAGE(!PageMovableOpsIsolated(page), page);
>  	folio_lock(folio);
>  	page_movable_ops(page)->putback_page(page);
> -	ClearPageIsolated(page);
> +	ClearPageMovableOpsIsolated(page);
>  	folio_unlock(folio);
>  	folio_put(folio);
>  }
> @@ -216,10 +216,10 @@ static int migrate_movable_ops_page(struct page *dst, struct page *src,
>  	int rc = MIGRATEPAGE_SUCCESS;
>
>  	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(src), src);
> -	VM_WARN_ON_ONCE_PAGE(!PageIsolated(src), src);
> +	VM_WARN_ON_ONCE_PAGE(!PageMovableOpsIsolated(src), src);
>  	rc = page_movable_ops(src)->migrate_page(dst, src, mode);
>  	if (rc == MIGRATEPAGE_SUCCESS)
> -		ClearPageIsolated(src);
> +		ClearPageMovableOpsIsolated(src);
>  	return rc;
>  }
>
> --
> 2.49.0
>