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Wed, 25 Mar 2026 11:42:24 +0000 (UTC) Received: from p1.redhat.com (unknown [10.2.14.4]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 7EABF18002A6; Wed, 25 Mar 2026 11:42:08 +0000 (UTC) From: Nico Pache To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, npache@redhat.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com, "Lorenzo Stoakes (Oracle)" Subject: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() Date: Wed, 25 Mar 2026 05:40:22 -0600 Message-ID: <20260325114022.444081-6-npache@redhat.com> In-Reply-To: <20260325114022.444081-1-npache@redhat.com> References: <20260325114022.444081-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: SPUO0jfBWkLim0Ep6Iojz1_3Tlu7rv2frbjEdXLndA4_1774438945 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9AD6018000C X-Stat-Signature: 4r8ijduhti7ockzx68mmeymkiziwme65 X-Rspam-User: X-HE-Tag: 1774438955-820169 X-HE-Meta: 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 w1XGC76r 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The khugepaged daemon and madvise_collapse have two different implementations that do almost the same thing. Create collapse_single_pmd to increase code reuse and create an entry point to these two users. Refactor madvise_collapse and collapse_scan_mm_slot to use the new collapse_single_pmd function. To help reduce confusion around the mmap_locked variable, we rename mmap_locked to lock_dropped in the collapse_scan_mm_slot() function, and remove the redundant mmap_locked in madvise_collapse(); this further unifies the code readiblity. the SCAN_PTE_MAPPED_HUGEPAGE enum is no longer reachable in the madvise_collapse() function, so we drop it from the list of "continuing" enums. This introduces a minor behavioral change that is most likely an undiscovered bug. The current implementation of khugepaged tests collapse_test_exit_or_disable() before calling collapse_pte_mapped_thp, but we weren't doing it in the madvise_collapse case. By unifying these two callers madvise_collapse now also performs this check. We also modify the return value to be SCAN_ANY_PROCESS which properly indicates that this process is no longer valid to operate on. By moving the madvise_collapse writeback-retry logic into the helper function we can also avoid having to revalidate the VMA. We guard the khugepaged_pages_collapsed variable to ensure its only incremented for khugepaged. As requested we also convert a VM_BUG_ON to a VM_WARN_ON. Reviewed-by: Lorenzo Stoakes (Oracle) Reviewed-by: Lance Yang Reviewed-by: Baolin Wang Acked-by: David Hildenbrand (Arm) Signed-off-by: Nico Pache --- mm/khugepaged.c | 142 ++++++++++++++++++++++++------------------------ 1 file changed, 72 insertions(+), 70 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 3728a2cf133c..d06d84219e1b 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1257,7 +1257,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a static enum scan_result collapse_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long start_addr, - bool *mmap_locked, struct collapse_control *cc) + bool *lock_dropped, struct collapse_control *cc) { pmd_t *pmd; pte_t *pte, *_pte; @@ -1432,7 +1432,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, result = collapse_huge_page(mm, start_addr, referenced, unmapped, cc); /* collapse_huge_page will return with the mmap_lock released */ - *mmap_locked = false; + *lock_dropped = true; } out: trace_mm_khugepaged_scan_pmd(mm, folio, referenced, @@ -2424,6 +2424,67 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, return result; } +/* + * Try to collapse a single PMD starting at a PMD aligned addr, and return + * the results. + */ +static enum scan_result collapse_single_pmd(unsigned long addr, + struct vm_area_struct *vma, bool *lock_dropped, + struct collapse_control *cc) +{ + struct mm_struct *mm = vma->vm_mm; + bool triggered_wb = false; + enum scan_result result; + struct file *file; + pgoff_t pgoff; + + mmap_assert_locked(mm); + + if (vma_is_anonymous(vma)) { + result = collapse_scan_pmd(mm, vma, addr, lock_dropped, cc); + goto end; + } + + file = get_file(vma->vm_file); + pgoff = linear_page_index(vma, addr); + + mmap_read_unlock(mm); + *lock_dropped = true; +retry: + result = collapse_scan_file(mm, addr, file, pgoff, cc); + + /* + * For MADV_COLLAPSE, when encountering dirty pages, try to writeback, + * then retry the collapse one time. + */ + if (!cc->is_khugepaged && result == SCAN_PAGE_DIRTY_OR_WRITEBACK && + !triggered_wb && mapping_can_writeback(file->f_mapping)) { + const loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; + const loff_t lend = lstart + HPAGE_PMD_SIZE - 1; + + filemap_write_and_wait_range(file->f_mapping, lstart, lend); + triggered_wb = true; + goto retry; + } + fput(file); + + if (result == SCAN_PTE_MAPPED_HUGEPAGE) { + mmap_read_lock(mm); + if (collapse_test_exit_or_disable(mm)) + result = SCAN_ANY_PROCESS; + else + result = try_collapse_pte_mapped_thp(mm, addr, + !cc->is_khugepaged); + if (result == SCAN_PMD_MAPPED) + result = SCAN_SUCCEED; + mmap_read_unlock(mm); + } +end: + if (cc->is_khugepaged && result == SCAN_SUCCEED) + ++khugepaged_pages_collapsed; + return result; +} + static void collapse_scan_mm_slot(unsigned int progress_max, enum scan_result *result, struct collapse_control *cc) __releases(&khugepaged_mm_lock) @@ -2485,46 +2546,21 @@ static void collapse_scan_mm_slot(unsigned int progress_max, VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK); while (khugepaged_scan.address < hend) { - bool mmap_locked = true; + bool lock_dropped = false; cond_resched(); if (unlikely(collapse_test_exit_or_disable(mm))) goto breakouterloop; - VM_BUG_ON(khugepaged_scan.address < hstart || + VM_WARN_ON_ONCE(khugepaged_scan.address < hstart || khugepaged_scan.address + HPAGE_PMD_SIZE > hend); - if (!vma_is_anonymous(vma)) { - struct file *file = get_file(vma->vm_file); - pgoff_t pgoff = linear_page_index(vma, - khugepaged_scan.address); - - mmap_read_unlock(mm); - mmap_locked = false; - *result = collapse_scan_file(mm, - khugepaged_scan.address, file, pgoff, cc); - fput(file); - if (*result == SCAN_PTE_MAPPED_HUGEPAGE) { - mmap_read_lock(mm); - if (collapse_test_exit_or_disable(mm)) - goto breakouterloop; - *result = try_collapse_pte_mapped_thp(mm, - khugepaged_scan.address, false); - if (*result == SCAN_PMD_MAPPED) - *result = SCAN_SUCCEED; - mmap_read_unlock(mm); - } - } else { - *result = collapse_scan_pmd(mm, vma, - khugepaged_scan.address, &mmap_locked, cc); - } - - if (*result == SCAN_SUCCEED) - ++khugepaged_pages_collapsed; + *result = collapse_single_pmd(khugepaged_scan.address, + vma, &lock_dropped, cc); /* move to next address */ khugepaged_scan.address += HPAGE_PMD_SIZE; - if (!mmap_locked) + if (lock_dropped) /* * We released mmap_lock so break loop. Note * that we drop mmap_lock before all hugepage @@ -2799,7 +2835,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, unsigned long hstart, hend, addr; enum scan_result last_fail = SCAN_FAIL; int thps = 0; - bool mmap_locked = true; BUG_ON(vma->vm_start > start); BUG_ON(vma->vm_end < end); @@ -2821,13 +2856,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { enum scan_result result = SCAN_FAIL; - bool triggered_wb = false; -retry: - if (!mmap_locked) { + if (*lock_dropped) { cond_resched(); mmap_read_lock(mm); - mmap_locked = true; + *lock_dropped = false; result = hugepage_vma_revalidate(mm, addr, false, &vma, cc); if (result != SCAN_SUCCEED) { @@ -2837,45 +2870,14 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); } - mmap_assert_locked(mm); - if (!vma_is_anonymous(vma)) { - struct file *file = get_file(vma->vm_file); - pgoff_t pgoff = linear_page_index(vma, addr); - mmap_read_unlock(mm); - mmap_locked = false; - *lock_dropped = true; - result = collapse_scan_file(mm, addr, file, pgoff, cc); - - if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && - mapping_can_writeback(file->f_mapping)) { - loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; - loff_t lend = lstart + HPAGE_PMD_SIZE - 1; - - filemap_write_and_wait_range(file->f_mapping, lstart, lend); - triggered_wb = true; - fput(file); - goto retry; - } - fput(file); - } else { - result = collapse_scan_pmd(mm, vma, addr, &mmap_locked, cc); - } - if (!mmap_locked) - *lock_dropped = true; + result = collapse_single_pmd(addr, vma, lock_dropped, cc); -handle_result: switch (result) { case SCAN_SUCCEED: case SCAN_PMD_MAPPED: ++thps; break; - case SCAN_PTE_MAPPED_HUGEPAGE: - BUG_ON(mmap_locked); - mmap_read_lock(mm); - result = try_collapse_pte_mapped_thp(mm, addr, true); - mmap_read_unlock(mm); - goto handle_result; /* Whitelisted set of results where continuing OK */ case SCAN_NO_PTE_TABLE: case SCAN_PTE_NON_PRESENT: @@ -2898,7 +2900,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, out_maybelock: /* Caller expects us to hold mmap_lock on return */ - if (!mmap_locked) + if (*lock_dropped) mmap_read_lock(mm); out_nolock: mmap_assert_locked(mm); -- 2.53.0