linux-kernel - Re: [PATCH 8/8] mm: Remove PG

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Message-ID: <Z4UxK_bsFD7TtL1l@casper.infradead.org>
Date: Mon, 13 Jan 2025 15:28:43 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Andi Shyti <andi.shyti@...ux.intel.com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Christian Brauner <brauner@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	David Airlie <airlied@...il.com>,
	David Hildenbrand <david@...hat.com>, Hao Ge <gehao@...inos.cn>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Josef Bacik <josef@...icpanda.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Miklos Szeredi <miklos@...redi.hu>, Nhat Pham <nphamcs@...il.com>,
	Oscar Salvador <osalvador@...e.de>,
	Ran Xiaokai <ran.xiaokai@....com.cn>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Simona Vetter <simona@...ll.ch>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Vlastimil Babka <vbabka@...e.cz>,
	Yosry Ahmed <yosryahmed@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 8/8] mm: Remove PG_reclaim

On Mon, Jan 13, 2025 at 11:34:53AM +0200, Kirill A. Shutemov wrote:
> diff --git a/mm/migrate.c b/mm/migrate.c
> index caadbe393aa2..beba72da5e33 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -686,6 +686,8 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
>  		folio_set_young(newfolio);
>  	if (folio_test_idle(folio))
>  		folio_set_idle(newfolio);
> +	if (folio_test_readahead(folio))
> +		folio_set_readahead(newfolio);
>  
>  	folio_migrate_refs(newfolio, folio);
>  	/*

Not a problem with this patch ... but aren't we missing a
test_dropbehind / set_dropbehind pair in this function?  Or are we
prohibited from migrating a folio with the dropbehind flag set
somewhere?

> +++ b/mm/swap.c
> @@ -221,22 +221,6 @@ static void lru_move_tail(struct lruvec *lruvec, struct folio *folio)
>  	__count_vm_events(PGROTATED, folio_nr_pages(folio));
>  }
>  
> -/*
> - * Writeback is about to end against a folio which has been marked for
> - * immediate reclaim.  If it still appears to be reclaimable, move it
> - * to the tail of the inactive list.
> - *
> - * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
> - */
> -void folio_rotate_reclaimable(struct folio *folio)
> -{
> -	if (folio_test_locked(folio) || folio_test_dirty(folio) ||
> -	    folio_test_unevictable(folio))
> -		return;
> -
> -	folio_batch_add_and_move(folio, lru_move_tail, true);
> -}

I think this is the last caller of lru_move_tail(), which means we can
get rid of fbatches->lru_move_tail and the local_lock that protects it.
Or did I miss something?