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Message-ID: <Y2LWonzCdWkDwyyr@x1n>
Date: Wed, 2 Nov 2022 16:44:18 -0400
From: Peter Xu <peterx@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
Hugh Dickins <hughd@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>
Subject: Re: [PATCH 3/5] userfualtfd: Replace lru_cache functions with
folio_add functions
On Wed, Nov 02, 2022 at 07:21:19PM +0000, Matthew Wilcox wrote:
> On Wed, Nov 02, 2022 at 03:02:35PM -0400, Peter Xu wrote:
> > Does the patch attached look reasonable to you?
>
> Mmm, no. If the page is in the swap cache, this will be "true".
It will not happen in practise, right?
I mean, shmem_get_folio() should have done the swap-in, and we should have
the page lock held at the meantime.
For anon, mcopy_atomic_pte() is the only user and it's passing in a newly
allocated page here.
>
> > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> > index 3d0fef3980b3..650ab6cfd5f4 100644
> > --- a/mm/userfaultfd.c
> > +++ b/mm/userfaultfd.c
> > @@ -64,7 +64,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
> > pte_t _dst_pte, *dst_pte;
> > bool writable = dst_vma->vm_flags & VM_WRITE;
> > bool vm_shared = dst_vma->vm_flags & VM_SHARED;
> > - bool page_in_cache = page->mapping;
> > + bool page_in_cache = page_mapping(page);
>
> We could do:
>
> struct page *head = compound_head(page);
> bool page_in_cache = head->mapping && !PageMappingFlags(head);
Sounds good to me, but it just gets a bit complicated.
If page_mapping() doesn't sound good, how about we just pass that over from
callers? We only have three, so quite doable too.
--
Peter Xu
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