linux-kernel - Re: [PATCH 4/9] mm, swap: tidy up swap device and cluster info helpers

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Message-ID: <aK+YzeWToVUX3WOY@MiWiFi-R3L-srv>
Date: Thu, 28 Aug 2025 07:46:21 +0800
From: Baoquan He <bhe@...hat.com>
To: Chris Li <chrisl@...nel.org>
Cc: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Barry Song <baohua@...nel.org>,
	Nhat Pham <nphamcs@...il.com>,
	Kemeng Shi <shikemeng@...weicloud.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Hildenbrand <david@...hat.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Zi Yan <ziy@...dia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] mm, swap: tidy up swap device and cluster info
 helpers

On 08/27/25 at 10:44am, Chris Li wrote:
> On Tue, Aug 26, 2025 at 8:47 PM Baoquan He <bhe@...hat.com> wrote:
> >
> > On 08/23/25 at 03:20am, Kairui Song wrote:
> > ......
> > > diff --git a/mm/swap.h b/mm/swap.h
> > > index 223b40f2d37e..7b3efaa51624 100644
> > > --- a/mm/swap.h
> > > +++ b/mm/swap.h
> > > @@ -15,6 +15,8 @@ extern int page_cluster;
> > >  #define swap_entry_order(order)      0
> > >  #endif
> > >
> > > +extern struct swap_info_struct *swap_info[];
> > > +
> > >  /*
> > >   * We use this to track usage of a cluster. A cluster is a block of swap disk
> > >   * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
> > > @@ -53,9 +55,28 @@ enum swap_cluster_flags {
> > >  #include <linux/swapops.h> /* for swp_offset */
> > >  #include <linux/blk_types.h> /* for bio_end_io_t */
> > >
> > > +/*
> > > + * Callers of all swp_* helpers here must ensure the entry is valid, and
> > > + * pin the swap device by reference or in other ways.
> > > + */
> > > +static inline struct swap_info_struct *swp_type_info(int type)
> > > +{
> > > +     struct swap_info_struct *si;
> > > +
> > > +     si = READ_ONCE(swap_info[type]); /* rcu_dereference() */
> > > +     VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
> > > +     return si;
> > > +}
> > > +
> > > +static inline struct swap_info_struct *swp_info(swp_entry_t entry)
> > > +{
> > > +     return swp_type_info(swp_type(entry));
> > > +}
> >
> > swp_type_info() is only used by swp_info() in the whole series, can we
> > open code it in swp_info()?
> 
> BTW, off topic here. I really don't like the "_info" suffix. Anything
> you can put into a C struct by definition is some kind of information.
> Same to the _struct. Anything defined by a struct is a struct. Don't
> need to say that.
> The "struct swap_info_struct" gets two of the unnecessary words. It
> should be something like  "struct swap_file" or "struct swap_device".
> Renaming it is too invasive to the code base and it will mess up the
> git annotation history.

I agree. I searched for _info_struct in the current code, only found
swap_info_struct, ax25_info_struct, vm86plus_info_struct. The latter two
are seen in very few LOC. Maybe we can rename it later when things are all
done. And 'struct swap_cluster_info' too.