linux-kernel - Re: [PATCH v3 06/11] powerpc/ptdump: rename "struct pgtable_level" to "struct ptdump

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Message-ID: <e97675f8-ba69-464e-982c-8a8bdfbb2547@lucifer.local>
Date: Tue, 12 Aug 2025 19:54:58 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, xen-devel@...ts.xenproject.org,
        linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linuxppc-dev@...ts.ozlabs.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "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>,
        Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
        Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
        Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v3 06/11] powerpc/ptdump: rename "struct pgtable_level"
 to "struct ptdump_pglevel"

On Tue, Aug 12, 2025 at 08:39:36PM +0200, Christophe Leroy wrote:
> Hi Lorenzo,
>
> Le 12/08/2025 à 20:23, Lorenzo Stoakes a écrit :
> > On Mon, Aug 11, 2025 at 01:26:26PM +0200, David Hildenbrand wrote:
> > > We want to make use of "pgtable_level" for an enum in core-mm. Other
> > > architectures seem to call "struct pgtable_level" either:
> > > * "struct pg_level" when not exposed in a header (riscv, arm)
> > > * "struct ptdump_pg_level" when expose in a header (arm64)
> > >
> > > So let's follow what arm64 does.
> > >
> > > Signed-off-by: David Hildenbrand <david@...hat.com>
> >
> > This LGTM, but I'm super confused what these are for, they don't seem to be
> > used anywhere? Maybe I'm missing some macro madness, but it seems like dead
> > code anyway?
>
> pg_level[] are used several times in arch/powerpc/mm/ptdump/ptdump.c, for
> instance here:
>
> static void note_page_update_state(struct pg_state *st, unsigned long addr,
> int level, u64 val)
> {
> 	u64 flag = level >= 0 ? val & pg_level[level].mask : 0;
> 	u64 pa = val & PTE_RPN_MASK;
>
> 	st->level = level;
> 	st->current_flags = flag;
> 	st->start_address = addr;
> 	st->start_pa = pa;
>
> 	while (addr >= st->marker[1].start_address) {
> 		st->marker++;
> 		pt_dump_seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
> 	}
> }
>

Ahhhh ok so you're _always_ happening to reference a field in the global value,
thereby not referencing the _type_ anywhere but referencing fields of the
global.

Thanks, that clears that up! :)