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Date: Wed, 20 Mar 2024 13:00:58 +0000
From: Matthew Wilcox <willy@infradead.org>
To: alexs@kernel.org
Cc: Izik Eidus <izik.eidus@ravellosystems.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Hugh Dickins <hughd@google.com>, Chris Wright <chrisw@sous-sol.org>,
	kasong@tencent.com, Andrew Morton <akpm@linux-foundation.org>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/11] mm/ksm: use a folio in remove_stable_node
Message-ID: <ZfreCicoK9C6GW1t@casper.infradead.org>
References: <20240320074049.4130552-1-alexs@kernel.org>
 <20240320074049.4130552-4-alexs@kernel.org>
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In-Reply-To: <20240320074049.4130552-4-alexs@kernel.org>

On Wed, Mar 20, 2024 at 03:40:39PM +0800, alexs@kernel.org wrote:
> @@ -1124,22 +1124,22 @@ static int remove_stable_node(struct ksm_stable_node *stable_node)
>  	 * merge_across_nodes/max_page_sharing be switched.
>  	 */
>  	err = -EBUSY;
> -	if (!page_mapped(page)) {
> +	if (!folio_mapped(folio)) {
>  		/*
>  		 * The stable node did not yet appear stale to get_ksm_page(),
> -		 * since that allows for an unmapped ksm page to be recognized
> +		 * since that allows for an unmapped ksm folio to be recognized
>  		 * right up until it is freed; but the node is safe to remove.
> -		 * This page might be in an LRU cache waiting to be freed,
> +		 * This folio might be in an LRU cache waiting to be freed,
>  		 * or it might be PageSwapCache (perhaps under writeback),

s/PageSwapCache/in the swapcache/

>  		 * or it might have been removed from swapcache a moment ago.
>  		 */
> -		set_page_stable_node(page, NULL);
> +		set_page_stable_node(&folio->page, NULL);

Before this patch, introduce a folio_set_stable_node() (and convert the
one caller which already has a folio).  I'd do it the other way around
from ksm_get_folio(); that is:

static inline void folio_set_stable_node(struct folio *folio,
		struct ksm_stable_node *stable_node)
{
	set_page_stable_node(&folio->page, stable_node);
}

and then we can merge the two later when there are no more calls to
set_page_stable_node().