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Mon, 09 Feb 2026 02:49:13 -0800 (PST) MIME-Version: 1.0 References: <142919ac14d3cf70cba370808d85debe089df7b4.1766631066.git.baolin.wang@linux.alibaba.com> <20260116162652.176054-1-baolin.wang@linux.alibaba.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Mon, 9 Feb 2026 18:49:01 +0800 X-Gm-Features: AZwV_QhWVdqt_7RuXV7-kVSLDw48X3tEZAOO_6ZSqGLxObnJZ5IOCtH-TVz0o1s Message-ID: Subject: Re: [PATCH] mm: rmap: skip batched unmapping for UFFD vmas To: "David Hildenbrand (Arm)" Cc: Baolin Wang , Liam.Howlett@oracle.com, akpm@linux-foundation.org, catalin.marinas@arm.com, dev.jain@arm.com, harry.yoo@oracle.com, jannh@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, riel@surriel.com, rppt@kernel.org, ryan.roberts@arm.com, surenb@google.com, vbabka@suse.cz, will@kernel.org, willy@infradead.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam11 X-Stat-Signature: 73u9seng5zfhp6am1wxiwtkrswb9ju1h X-Rspam-User: X-Rspamd-Queue-Id: 76E2C4000A X-HE-Tag: 1770634154-932410 X-HE-Meta: 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 i8GBR7ij ajSBAXQjmhJi69ZCzXR8F06FD/2r0LZFo95K4ty5jrkUpNoDNBA68tOFenymbXB65Gbb5yA8x4MT/LyOE8D2C6+xeQ1A5uKajsT4iIwXycHnczV0JhuTxkZfeyw+rYNCV89Ptn81j1QetdVa+MWJw3mPcXW1KnDUhVSinPPLf/WB5+uNnyLxlZCFUWYD4SLFvr0dBEe6mHH4fYD2Hyidm79xcBuS/Wq3rKrZZ0pcBT6GkabLJltT05ovzML6ZJE9ugIPMt4W32LvGIBXZg7A1J5GwQ76Guz00RaGwm8BS3Y26wSwv1zUBXk7ks9/UxJMym89EEqinHRCgWMw9uplncION+4erBqeuFEIK2Pi+c6OgVZ7DGH+tgq3dTouTACqJytUBlG2j6zVUgBSFhWSRxdnucJo3HuBmfBy/yhBHeEOrfZpk8fJXqbfgTDIN3cdtjnnYi0xP/srGP6pINpnFlrtLhQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Feb 9, 2026 at 5:54=E2=80=AFPM David Hildenbrand (Arm) wrote: > > On 1/16/26 17:26, Baolin Wang wrote: > > As Dev reported[1], it's not ready to support batched unmapping for uff= d case. > > Let's still fallback to per-page unmapping for the uffd case. > > > > [1] https://lore.kernel.org/linux-mm/20260116082721.275178-1-dev.jain@a= rm.com/ > > Reported-by: Dev Jain > > Suggested-by: Barry Song > > Signed-off-by: Baolin Wang > > --- > > mm/rmap.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > index f13480cb9f2e..172643092dcf 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1953,6 +1953,9 @@ static inline unsigned int folio_unmap_pte_batch(= struct folio *folio, > > if (pte_unused(pte)) > > return 1; > > > > + if (userfaultfd_wp(vma)) > > + return 1; > > + > > Interesting. I was just wondering why we didn't run into that with lazyfr= ee folios. > > Staring at pte_install_uffd_wp_if_needed(), we never set the marker for > anonymous VMAs. > > So, yeah, if one sets lazyfree on a uffd-wp PTE, the uffd-wp bit will jus= t get > zapped alongside. Just like MADV_DONTNEED. > > > I'm fine with that temporary fix. But I guess the non-hacky way to handle= this would be: > > > From 53d016d6e6f624425dbdbc2fb1dec7c91fbef15c Mon Sep 17 00:00:00 2001 > From: "David Hildenbrand (Arm)" > Date: Mon, 9 Feb 2026 10:52:59 +0100 > Subject: [PATCH] tmp > > Signed-off-by: David Hildenbrand (Arm) > --- > include/linux/mm_inline.h | 15 ++++++--------- > mm/memory.c | 21 +-------------------- > mm/rmap.c | 2 +- > 3 files changed, 8 insertions(+), 30 deletions(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index fa2d6ba811b5..8a9a2c5f5ee3 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -566,9 +566,8 @@ static inline pte_marker copy_pte_marker( > * > * Returns true if an uffd-wp pte was installed, false otherwise. > */ > -static inline bool > -pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long = addr, > - pte_t *pte, pte_t pteval) > +static inline bool install_uffd_wp_ptes_if_needed(struct vm_area_struct = *vma, > + unsigned long addr, pte_t *pte, unsigned int nr, pte_t pt= eval) > { > bool arm_uffd_pte =3D false; > > @@ -598,13 +597,11 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct= *vma, unsigned long addr, > if (unlikely(pte_swp_uffd_wp_any(pteval))) > arm_uffd_pte =3D true; > > - if (unlikely(arm_uffd_pte)) { > - set_pte_at(vma->vm_mm, addr, pte, > - make_pte_marker(PTE_MARKER_UFFD_WP)); > - return true; > - } > + if (likely(!arm_uffd_pte)) > + return false; > > - return false; > + set_ptes(vma->vm_mm, addr, pte, make_pte_marker(PTE_MARKER_UFFD_W= P), nr); > + return true; > } > > static inline bool vma_has_recency(const struct vm_area_struct *vma) > diff --git a/mm/memory.c b/mm/memory.c > index da360a6eb8a4..0a87d02a9a69 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1592,29 +1592,10 @@ zap_install_uffd_wp_if_needed(struct vm_area_stru= ct *vma, > unsigned long addr, pte_t *pte, int nr, > struct zap_details *details, pte_t pteval) > { > - bool was_installed =3D false; > - > - if (!uffd_supports_wp_marker()) > - return false; > - > - /* Zap on anonymous always means dropping everything */ > - if (vma_is_anonymous(vma)) > - return false; > - > if (zap_drop_markers(details)) > return false; > > - for (;;) { > - /* the PFN in the PTE is irrelevant. */ > - if (pte_install_uffd_wp_if_needed(vma, addr, pte, pteval)= ) > - was_installed =3D true; > - if (--nr =3D=3D 0) > - break; > - pte++; > - addr +=3D PAGE_SIZE; > - } > - > - return was_installed; > + return install_uffd_wp_ptes_if_needed(vma, addr, pte, nr, pteval)= ; > } > > static __always_inline void zap_present_folio_ptes(struct mmu_gather *t= lb, > diff --git a/mm/rmap.c b/mm/rmap.c > index 7b9879ef442d..f71aacf35925 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2061,7 +2061,7 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, > * we may want to replace a none pte with a marker pte if > * it's file-backed, so we don't lose the tracking info. > */ > - pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pte= val); > + install_uffd_wp_ptes_if_needed(vma, address, pvmw.pte, nr= _pages, pteval); > > /* Update high watermark before we lower rss */ > update_hiwater_rss(mm); > -- > 2.43.0 > > > > Does somebody have time to look into that? We should also adjust the doc = of pte_install_uffd_wp_if_needed() > and turn it into some proper kerneldoc. I'd nominate Dev, if he has the time, as he has been working on related changes and is already familiar with this area :-) https://lore.kernel.org/linux-mm/20260116082721.275178-1-dev.jain@arm.com/ I assume this could be treated as a separate optimization, as the current temporary fix seems acceptable? Thanks Barry