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b=d39AbULaWTxHR69m1JKeOsmspto3HCcwxUHZ8hYeOSf2twIHEp9q0LF2UwS/CKzJs mAL7JXhCOj69MhzumwiVKU+CkfQSLeqYf6X2w9CbY59cNrq2F1V9f49u/iSklok/Y1 /s8exz9tR4Z6lEiU1Yz1acsa2ff70/f4XV45GlS8NyaxVyLlgrgZJD0cIBpA1rGvDU sNR401hsTdbg+zrZC53pnJcfbvsEM5f3i5jOrsT3fZ9M2AOwMFhfz4e8NJvEHYuUMJ zmKmUZEIfIrHc9NH4ga+hdBSYQ/JV6UUM33niB2J0Cm/o3HdNfhC3WGGN4lUA3/+ra bkuLSIJlefT7g== Message-ID: <7e5f27b5-392e-43bd-8a47-b81395dbf9a7@kernel.org> Date: Mon, 9 Feb 2026 11:58:20 +0100 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> 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 References: <142919ac14d3cf70cba370808d85debe089df7b4.1766631066.git.baolin.wang@linux.alibaba.com> <20260116162652.176054-1-baolin.wang@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Stat-Signature: gfqzjta9hxcnxu33caxim3y9ercn33hn X-Rspam-User: X-Rspamd-Queue-Id: 82585180011 X-HE-Tag: 1770634708-466201 X-HE-Meta: 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 SSqk3s7K pG1NrCfm9sUXtbopmQoIzCphA0+jLl+ClAeGOpYhmEj3rvST2BSjSm74Y6FpIDmGHP6R8y6KHxJhvmv45myG6EBShkS/OGMIj2M4EVyP1D2WYGtsHp7BXfP87e46jd/utg2G+0TyzeUI9kcIMQz+6SKHsY7SZK42jdF+yUTx7XV8m509SB6PA7TgCCqJoG9C0ZlKf0pEaZj+S20BxGnqY9vxfJNjxISv5ApKHG+dZGUF3Db761aSImRLkPMDUdGIKIhNdMSHEI3Cla5ENfJAf6MINGsGUYbnFFLB9r0yXlk1oWpyq20dSG68m0GQ1ZAE2gmt2jelEv517D0gEPOG1vY3dFcIO51lyElUA 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 2/9/26 11:49, 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/ > > I assume this could be treated as a separate optimization, as > the current temporary fix seems acceptable? Let's call it a cleanup, because the way try_to_unmap_one() sometimes respects "nr_pages" and sometimes doesn't (because it's hidden somewhere that nr_pages will be 1) is just nasty and provoked the bug you ran into in the first place. :) -- Cheers, David