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

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Message-ID: <CACePvbU8pnjWCiWcSXRr4UdpuD_wdtrouLMz_fNB_=KRrdHLmQ@mail.gmail.com>
Date: Wed, 27 Aug 2025 10:44:50 -0700
From: Chris Li <chrisl@...nel.org>
To: Baoquan He <bhe@...hat.com>
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 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.

Oh well.

Chris