linux-kernel - Re: [PATCH v2 08/40] mm/memory: page_add_file_rmap() -> folio_add_file_rmap

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Message-ID: <ZrZSx7T8EjFrIFAE@google.com>
Date: Fri, 9 Aug 2024 18:32:55 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: g@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Hugh Dickins <hughd@...gle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Muchun Song <muchun.song@...ux.dev>, Peter Xu <peterx@...hat.com>,
	surenb@...gle.com
Subject: Re: [PATCH v2 08/40] mm/memory: page_add_file_rmap() ->
 folio_add_file_rmap_[pte|pmd]()

On Fri, Aug 09, 2024 at 07:27:27PM +0200, David Hildenbrand wrote:
> On 09.08.24 19:13, Vincent Donnefort wrote:
> > Hi,
> > 
> > Sorry, reviving this thread as I have ran into something weird:
> > 
> > On Wed, Dec 20, 2023 at 11:44:32PM +0100, David Hildenbrand wrote:
> > > Let's convert insert_page_into_pte_locked() and do_set_pmd(). While at it,
> > > perform some folio conversion.
> > > 
> > > Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>
> > > Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> > > Signed-off-by: David Hildenbrand <david@...hat.com>
> > > ---
> > >   mm/memory.c | 14 ++++++++------
> > >   1 file changed, 8 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index 7f957e5a84311..c77d3952d261f 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > 
> > [...]
> > 
> > >   vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
> > >   {
> > > +	struct folio *folio = page_folio(page);
> > >   	struct vm_area_struct *vma = vmf->vma;
> > >   	bool write = vmf->flags & FAULT_FLAG_WRITE;
> > >   	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
> > > @@ -4418,8 +4421,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
> > >   	if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
> > >   		return ret;
> > > -	page = compound_head(page);
> > > -	if (compound_order(page) != HPAGE_PMD_ORDER)
> > > +	if (page != &folio->page || folio_order(folio) != HPAGE_PMD_ORDER)
> > >   		return ret;
> > 
> > Is this `page != &folio->page` expected? I believe this check wasn't there
> > before as we had `page = compound_head()`.
> > 
> > It breaks the installation of a PMD level mapping for shmem when the fault
> > address is in the middle of this block. In its fault path, shmem sets
> > 
> >    vmf->page = folio_file_page(folio, vmf->pgoff)
> > 
> > which fails this test above.
> 
> Already fixed? :)
> 
> commit ab1ffc86cb5bec1c92387b9811d9036512f8f4eb (tag:
> mm-hotfixes-stable-2024-06-26-17-28)
> Author: Andrew Bresticker <abrestic@...osinc.com>
> Date:   Tue Jun 11 08:32:16 2024 -0700
> 
>     mm/memory: don't require head page for do_set_pmd()
> 

Duh of course I haven't looked anything recent enough, my bad!

Thanks for your quick answer!

> 
> -- 
> Cheers,
> 
> David / dhildenb
>