linux-kernel - Re: [PATCH v1 05/29] mm/balloon_compaction: make PageOffline sticky until the page is freed

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Message-ID: <aGN8l3-a7GeFhFlz@hyeyoo>
Date: Tue, 1 Jul 2025 15:13:43 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Zi Yan <ziy@...dia.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        David Hildenbrand <david@...hat.com>, 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,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        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>,
        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>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Minchan Kim <minchan@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>, Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>, Peter Xu <peterx@...hat.com>,
        Xu Xin <xu.xin16@....com.cn>,
        Chengming Zhou <chengming.zhou@...ux.dev>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Naoya Horiguchi <nao.horiguchi@...il.com>,
        Oscar Salvador <osalvador@...e.de>, Rik van Riel <riel@...riel.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH v1 05/29] mm/balloon_compaction: make PageOffline sticky
 until the page is freed

On Mon, Jun 30, 2025 at 12:14:01PM -0400, Zi Yan wrote:
> On 30 Jun 2025, at 12:01, Lorenzo Stoakes wrote:
> 
> > On Mon, Jun 30, 2025 at 02:59:46PM +0200, David Hildenbrand wrote:
> >> Let the page freeing code handle clearing the page type.
> >
> > Why is this advantageous? We want to keep the page marked offline for longer?
> >
> >>
> >> Acked-by: Zi Yan <ziy@...dia.com>
> >> Acked-by: Harry Yoo <harry.yoo@...cle.com>
> >> Signed-off-by: David Hildenbrand <david@...hat.com>
> >
> > On assumption this UINT_MAX stuff is sane :)) I mean this is straightforward I
> > guess:
> 
> This is how page type is cleared.
> See: https://elixir.bootlin.com/linux/v6.15.4/source/include/linux/page-flags.h#L1013.
> 
> I agree with you that patch 4 should have a comment in free_pages_prepare()
> about what the code is for and why UINT_MAX is used.

Or instead of comment, maybe something like this:

/* Clear any page type */
static __always_inline void __ClearPageType(struct page *page)
{
	VM_WARN_ON_ONCE_PAGE(!page_has_type(page), page);
	page->page_type = UINT_MAX;
}

in patch 4:

if (unlikely(page_has_type(page)))
	__ClearPageType(page);

-- 
Cheers,
Harry / Hyeonggon