linux-kernel - Re: [PATCH v1 19/29] mm: stop storing migration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <aGUejyDVKGBFLp1b@hyeyoo>
Date: Wed, 2 Jul 2025 20:57:03 +0900
From: Harry Yoo <harry.yoo@...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,
        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>,
        Zi Yan <ziy@...dia.com>, 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>,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.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 19/29] mm: stop storing migration_ops in page->mapping

On Wed, Jul 02, 2025 at 01:51:52PM +0200, David Hildenbrand wrote:
> On 02.07.25 13:43, Harry Yoo wrote:
> > On Wed, Jul 02, 2025 at 01:04:05PM +0200, David Hildenbrand wrote:
> > > On 02.07.25 12:34, Harry Yoo wrote:
> > > > On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:
> > > > > ... instead, look them up statically based on the page type. Maybe in the
> > > > > future we want a registration interface? At least for now, it can be
> > > > > easily handled using the two page types that actually support page
> > > > > migration.
> > > > > 
> > > > > The remaining usage of page->mapping is to flag such pages as actually
> > > > > being movable (having movable_ops), which we will change next.
> > > > > 
> > > > > Reviewed-by: Zi Yan <ziy@...dia.com>
> > > > > Signed-off-by: David Hildenbrand <david@...hat.com>
> > > > > ---
> > > > 
> > > > > +static const struct movable_operations *page_movable_ops(struct page *page)
> > > > > +{
> > > > > +	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
> > > > > +
> > > > > +	/*
> > > > > +	 * If we enable page migration for a page of a certain type by marking
> > > > > +	 * it as movable, the page type must be sticky until the page gets freed
> > > > > +	 * back to the buddy.
> > > > > +	 */
> > > > > +#ifdef CONFIG_BALLOON_COMPACTION
> > > > > +	if (PageOffline(page))
> > > > > +		/* Only balloon compaction sets PageOffline pages movable. */
> > > > > +		return &balloon_mops;
> > > > > +#endif /* CONFIG_BALLOON_COMPACTION */
> > > > > +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
> > > > > +	if (PageZsmalloc(page))
> > > > > +		return &zsmalloc_mops;
> > > > > +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
> > > > 
> > > > What happens if:
> > > >     CONFIG_ZSMALLOC=y
> > > >     CONFIG_TRANSPARENT_HUGEPAGE=n
> > > >     CONFIG_COMPACTION=n
> > > >     CONFIG_MIGRATION=y
> > > 
> > > Pages are never allocated from ZONE_MOVABLE/CMA and
> > 
> > I don't understand how that's true, neither zram nor zsmalloc clears
> > __GFP_MOVABLE when CONFIG_COMPACTION=n?
> > 
> > ...Or perhaps I'm still missing some pieces ;)
> 
> You might have found a bug in zsmalloc then :) Without support for compaction, we
> must clear __GFP_MOVABLE in alloc_zpdesc() I assume.
> 
> Do you have the capacity to look into that and send a fix if really broken?

I'll add that to somehwere in my TODO list :)

1) confirming if it's really broken and
2) fixing it if so.
 
> In balloon compaction code we properly handle that.

-- 
Cheers,
Harry / Hyeonggon