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imf16.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf16.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770724892; a=rsa-sha256; cv=none; b=pUFdfE2V94W1MTJGThwHhw4nveAmp9LxjVKC0hjXBCVnie9PkFiNC8hMeEt+qdAn/YKi3B ALq2tu+AIYnAYCgd4md68rx2FWMq8GYuaNw4vN/ROKRPSUMmuYMA+I32LQrSDLL6fdNnup tt+mJHBrBwAawnrn9zAdUDwXeZpHxXk= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0C1BA339; Tue, 10 Feb 2026 04:01:24 -0800 (PST) Received: from [10.164.19.61] (unknown [10.164.19.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6A7E63F632; Tue, 10 Feb 2026 04:01:24 -0800 (PST) Message-ID: Date: Tue, 10 Feb 2026 17:31:21 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: rmap: skip batched unmapping for UFFD vmas To: Barry Song <21cnbao@gmail.com>, "David Hildenbrand (Arm)" Cc: Baolin Wang , Liam.Howlett@oracle.com, akpm@linux-foundation.org, catalin.marinas@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 References: <142919ac14d3cf70cba370808d85debe089df7b4.1766631066.git.baolin.wang@linux.alibaba.com> <20260116162652.176054-1-baolin.wang@linux.alibaba.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Stat-Signature: qtpnnz8iouux9q63anmdbp3bzgqs76x4 X-Rspam-User: X-Rspamd-Queue-Id: AA7FD18001D X-HE-Tag: 1770724891-291796 X-HE-Meta: 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 kXdWEdk+ rD+6U2Hp5sFz85s9Y58kP8B9CUn3OB5l0Oo/vKs/Le7plEhCqAOxQrgo2Xojms+E+6YeWgFPT13veuhKbeweJOOr0kJh3l+vvKBLbuOtF2+dPZ1DOjocjqXPPLiXFsKNMGkq3D0F/8TuQ42Bmi+rlmwNLh+IvYe8MsXhOSuN5qXJ8HO9/SEsmf5keQSsEkK6SlLeKTr45yLxjvSPqpm0J8e48dMGAl7pVMhETvIruay/AGrE= 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 09/02/26 4:19 pm, Barry Song wrote: > On Mon, Feb 9, 2026 at 5:54 PM 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 uffd 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@arm.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 lazyfree 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 just 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 pteval) >> { >> bool arm_uffd_pte = 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 = 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_WP), 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_struct *vma, >> unsigned long addr, pte_t *pte, int nr, >> struct zap_details *details, pte_t pteval) >> { >> - bool was_installed = 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 = true; >> - if (--nr == 0) >> - break; >> - pte++; >> - addr += 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 *tlb, >> 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, struct 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, pteval); >> + 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/ Indeed, I'll be taking a stab on the uffd batching, and the generic folio batching (meaning anon folios now). > > I assume this could be treated as a separate optimization, as > the current temporary fix seems acceptable? > > Thanks > Barry