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b=YEi+YEkR+oCasLray0lq+5kuo1+2wZ9JRos7Qg4UUWgwha+H9wKNwDVDaVRiQjhM0 v1qP22U72McErMgBo6jEMZ9ELTBCKF7d6geGf/b0NrhcNNuGf1oCXJmSvXezqJeye5 Q/CHgNU2V9CFScX8CF/IvI6TlvajmHjsJbOYGwTgatP05znUKtosMjHDxhpAkdDHwr dJpBpOgNqeM36k+CxQ2keQ2a3jR5O7gBS7CIYZ3bClGKgLM6r39yWfRGXnpFbJvwAv MWR4NcpHOwKXQMQPA4yvQ6TBZ8ZZJWZJm1gdWl1nuVjUvyWEaUjplrBLJMNmqNXnIi sqbN3ebOmZnvQ== Message-ID: <9d5a4703-a15e-4be6-926b-af2d98db40c0@kernel.org> Date: Tue, 31 Mar 2026 23:03:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() From: "David Hildenbrand (Arm)" To: "Lorenzo Stoakes (Oracle)" Cc: Nico Pache , linux-kernel@vger.kernel.org, linux-mm@kvack.org, 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, 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, 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 References: <20260325114022.444081-1-npache@redhat.com> <20260325114022.444081-6-npache@redhat.com> <7760c811-e100-4d40-9217-0813c28314be@lucifer.local> <0223d45b-e8b4-49a7-882b-477250d0c14d@kernel.org> <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> <440d6b8a-d299-43eb-83b5-6625f9468e5e@lucifer.local> <37132e09-9c03-4afc-bc73-4bca416c5343@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: z1wssy6azmoc368or5tcisojayyxy617 X-Rspamd-Queue-Id: 93F3A180008 X-Rspamd-Server: rspam09 X-HE-Tag: 1774991040-929628 X-HE-Meta: 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 ZAOLEH2I JN0FiCma9hPQVirICuLkbuJpiB+btHo/dNPNzxPJRZFuR0PTEDROHlaxMCrxghC+d5l18F5uoGgn/NzpHaJKdjXjAQQWKXaopsO8JFZFbLTiWBklt/BeeKJWcKhkVNz48OgSC6ixXi7LpPFGd1d61E5W2sJVBp+nFSb0lcRZp5HOFWGDdPz3tfJQXWLJeaEByHbS+G3ItiNnRBb57AMRxvC/FBP82XPBcZ9mkb8KRcHk7t7XbQGlBSzhuEGtP3ROtY0rqgejyosVxuX6lSIzktegNlD91uWt0bhR/XXF00zb8mRk8DqvUOoE8WbAGP2z7m64TG/mGvs8k7XvTx56v7vvzXg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/31/26 22:50, David Hildenbrand (Arm) wrote: > On 3/31/26 22:06, Lorenzo Stoakes (Oracle) wrote: >> On Tue, Mar 31, 2026 at 10:00:58PM +0200, David Hildenbrand (Arm) wrote: >>> >>> Right. >>> >>> The original code used >>> >>> bool mmap_locked = true; >>> >>> If the fix get squashed, maybe we should revert to that handling to >>> minimize the churn? >> >> Well collapse_single_pmd() and all descendents would need to be updated to >> invert the boolean, not sure it's worth it. > > The code is confusing me. > > In the old code, collapse_single_pmd() was called with "mmap_locked == > true" and set "mmap_locked=false". > > Now we call it with "mmap_unlocked=false" and it sets "mmap_unlocked=true". > > So far so good. > > However, collapse_scan_pmd() consumed "mmap_locked", now it effectively > consumes "mmap_unlocked". Okay, I'm too confused for today and give up :) FWIW, this is the effective change, and the effective changes to mmap_unlocked and lock_dropped ... confuse me: mm/khugepaged.c | 146 +++++++++++++++++++++++++----------------------- 1 file changed, 76 insertions(+), 70 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 26c38934e829..3ffff9f98b2f 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1253,7 +1253,7 @@ 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; @@ -1428,7 +1428,7 @@ 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, @@ -2420,6 +2420,67 @@ 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) @@ -2481,46 +2542,21 @@ 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 @@ -2795,7 +2831,7 @@ 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; + bool mmap_unlocked = false; BUG_ON(vma->vm_start > start); BUG_ON(vma->vm_end < end); @@ -2817,13 +2853,12 @@ 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 (mmap_unlocked) { cond_resched(); mmap_read_lock(mm); - mmap_locked = true; + mmap_unlocked = false; + *lock_dropped = true; result = hugepage_vma_revalidate(mm, addr, false, &vma, cc); if (result != SCAN_SUCCEED) { @@ -2833,45 +2868,14 @@ 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; + result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); - 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; - -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: @@ -2894,8 +2898,10 @@ 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 (mmap_unlocked) { + *lock_dropped = false; mmap_read_lock(mm); + } out_nolock: mmap_assert_locked(mm); mmdrop(mm); -- 2.43.0 -- Cheers, David