linux-kernel - Re: [PATCH 5/8] mm/vmscan: Use PG_dropbehind instead of PG

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Message-ID: <7b0e384b-6d42-48b7-ade0-f5a699bc369d@redhat.com>
Date: Mon, 13 Jan 2025 11:07:44 +0100
From: David Hildenbrand <david@...hat.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>
Cc: "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>,
 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 5/8] mm/vmscan: Use PG_dropbehind instead of PG_reclaim

On 13.01.25 10:34, Kirill A. Shutemov wrote:
> The recently introduced PG_dropbehind allows for freeing folios
> immediately after writeback. Unlike PG_reclaim, it does not need vmscan
> to be involved to get the folio freed.
> 
> Instead of using folio_set_reclaim(), use folio_set_dropbehind() in
> pageout().
> 
> It is safe to leave PG_dropbehind on the folio if, for some reason
> (bug?), the folio is not in a writeback state after ->writepage().
> In these cases, the kernel had to clear PG_reclaim as it shared a page
> flag bit with PG_readahead.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>   mm/vmscan.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a099876fa029..d15f80333d6b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -692,19 +692,16 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
>   		if (shmem_mapping(mapping) && folio_test_large(folio))
>   			wbc.list = folio_list;
>   
> -		folio_set_reclaim(folio);
> +		folio_set_dropbehind(folio);
> +
>   		res = mapping->a_ops->writepage(&folio->page, &wbc);
>   		if (res < 0)
>   			handle_write_error(mapping, folio, res);
>   		if (res == AOP_WRITEPAGE_ACTIVATE) {
> -			folio_clear_reclaim(folio);
> +			folio_clear_dropbehind(folio);
>   			return PAGE_ACTIVATE;
>   		}
>   
> -		if (!folio_test_writeback(folio)) {
> -			/* synchronous write or broken a_ops? */
> -			folio_clear_reclaim(folio);
> -		}
>   		trace_mm_vmscan_write_folio(folio);
>   		node_stat_add_folio(folio, NR_VMSCAN_WRITE);
>   		return PAGE_SUCCESS;

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb