Re: [PATCH v3 2/4] mm/util: introduce snapshot_page()

[David Hildenbrand]

On 16.07.25 19:36, Luiz Capitulino wrote:
> On 2025-07-16 06:16, David Hildenbrand wrote:
> > [...]
> >
> > > -dump:
> > > -    __dump_folio(foliop, &precise, pfn, idx);
> > > +    __dump_folio(&ps.folio_snapshot, &ps.page_snapshot, ps.pfn, ps.idx);
> >
> > Nit that can be cleaned up later on top:
> >
> > We should probably call this
> >
> > __dump_page_snapshot() and then just pass ... the page_snapshot.
> >
> > >    }
> > >    void dump_page(const struct page *page, const char *reason)
> > > diff --git a/mm/util.c b/mm/util.c
> > > index 0b270c43d7d1..f270bf42465b 100644
> > > --- a/mm/util.c
> > > +++ b/mm/util.c
> > > @@ -25,6 +25,7 @@
> > >    #include <linux/sizes.h>
> > >    #include <linux/compat.h>
> > >    #include <linux/fsnotify.h>
> > > +#include <linux/page_idle.h>
> > >    #include <linux/uaccess.h>
> > > @@ -1171,3 +1172,81 @@ int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma)
> > >        return 0;
> > >    }
> > >    EXPORT_SYMBOL(compat_vma_mmap_prepare);
> > > +
> > > +static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio,
> > > +             const struct page *page)
> > > +{
> > > +    /*
> > > +     * Only the first page of a high-order buddy page has PageBuddy() set.
> > > +     * So we have to check manually whether this page is part of a high-
> > > +     * order buddy page.
> > > +     */
> > > +    if (PageBuddy(page))
> > > +        ps->flags |= PAGE_SNAPSHOT_PG_BUDDY;
> > > +    else if (page_count(page) == 0 && is_free_buddy_page(page))
> > > +        ps->flags |= PAGE_SNAPSHOT_PG_BUDDY;
> > > +
> > > +    if (folio_test_idle(folio))
> > > +        ps->flags |= PAGE_SNAPSHOT_PG_IDLE;
> > > +}
> > > +
> > > +/**
> > > + * snapshot_page() - Create a snapshot of a struct page
> > > + * @ps: Pointer to a struct page_snapshot to store the page snapshot
> > > + * @page: The page to snapshot
> > > + *
> > > + * Create a snapshot of the page and store both its struct page and struct
> > > + * folio representations in @ps.
> > > + *
> > > + * Note that creating a faithful snapshot may fail if the compound
> >
> > Maybe highlight that this is not really expected to happen, ever.
> >
> > > + * state of the page keeps changing (e.g., due to a folio split). In
> > > + * this case, ps->faithful is set to false, and the snapshot assumes
> >
> > There is no ps->faithful.
>
> Yes, good catch. This was from an earlier version.
>
> Is it fine if I fix only this with a follow up patch for Andrew in this
> thread or would you prefer that I post v4 with all the other changes as
> well?

I think the series was part of mm-new, but now I only spot it in 
mm-everything, weird. Maybe because of a conflict with the other 
stable_page_flags() change?

So whatever Andrew prefers, really :)

--
Cheers,

David / dhildenb