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b=lSt1GlQ4liXpsZDHhaZWgURXXlZ5Z6t15x5uQx+s1UQxKmOZwdr8NSB1UiUpxi1Jc jgcWAgPCNDQln879JmTM8atfTpBTbY7s83G0WUPi2RnABmOsHCS3874Uwdm/1Mmf9d IvDptIkvfYcE8LozrUrIQjDsjN+wXOcepFZIyBw0dFHR6KS1WUe0/h4RFW2bW4U+0u mo4ROTN02Huy4sxYYD0PZMPJM3gHNv9N7VJcCjUpzO5EaDOrq4tNoU1eBgno94GgWc c3txEr4HGsOSFyXj+VnW6kEvjRx4Smd8cgGoqDNvzZwZ8zTCdDSLPViAHkalqJhIp3 2SZK+tjq29KXw== Message-ID: <81ff9caa-50f2-4951-8d82-2c8dcdf3db91@kernel.org> Date: Thu, 26 Feb 2026 10:40:57 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v2 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() To: Nico Pache , 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, 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: <20260226012929.169479-1-npache@redhat.com> <20260226012929.169479-6-npache@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260226012929.169479-6-npache@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: D805B1A0002 X-Stat-Signature: czij5gujek6omu3y1t4ic3d61w8gyj3x X-HE-Tag: 1772098871-311332 X-HE-Meta: U2FsdGVkX18Di20W1WIQxTNwq56uc9ysne33ngzTm77tK1zoA91gVI1VupIHGCXh4nS03ceAj4k8VJwVOxeqwv+uAgEdwfUDdzFaIEZSNDN5fbxzdPj3fcMN4ZmZGZZTLX0veeFON7fqhlI68wnwsmNnID39odcaHk6slFp2mtXw6o4W9bb16ANdlBl9kYue2tJIUNZ08fVpihXphMu94A0RqU7D7QMxwlwtxF2E597VyOo9PRL5tj4JY5d6GU4T6R1aQAZ8bb4CvwNn4kbMSLto/QbH7dtxv3Qgoek7ncNsSytOlpjI+mRhLcf5bM7u6Bm+uz2BEKFRXd+/cNSdrorYcg6hxsy2BvkMCNEtkL8ot1YIdoxZIJMq5x2M4s7OgIKttXl8ataQt6fmVUjFhETxvUel2b6xzXpqwvI5TNDtxhQMJIw9or9jbPqEmQ5YJb1aZb5Nr0Lqi5EzRhZll0pM/1Mj1Mqx9ZSEWc3VBLcDGaoq9QOdCDoEjpxeobGPohsBAW8uUx8Ae80aUj4ppGU5DI8dAPZr7T9KF+2zZTqo57Afa34yE6rNvvCSweKLe2Xu2YD95QUopsX2xa9uLoQR5ISUv3VLU+pFgyHN2YxcvpaRe+G45+Bq3CLehdR7LCC1yq8V2jESyQsx5PYV9qQ8aRhyVa+sDRQmTMvf7zQQwlJsOqxkMLApZmgGkNbU9s72VvWVtiGXbFcEf7/kcJDZX5Uz3Oj+m/8uCc407UovcZto+RE0iSqgnURxawIwNVJHYuspk53KDLlfbmccQ59yzKHyLpqMeQnCz0U8u1PjTpeeeJ0+SZnkZ3scJzdNuWQttxyCHtK++SyHkB11KdyBzo/f5vSUbv2Vc7ME2kZLNsKcFSSUwn0GnlPocirGpwxIYW9hM0rdCom7AKeStgLh5dG/0ONL6vntBJKp8zICanlpxw5XA1ybFV6TXMWZSTt9Dvu2xv6rQZK8LMR UN+GWhIH AowJQENv66eKOSk2ZsypjDWHE2G/QEUISSNJQ8fTgfQgMqBc4kGARMlyh0BoaPfZWCTo9g0xtXNygfdjXFspW4G8W+6Sr7qrYdjKwpjky/7AmedUB0JuGWnAnhaoJDgvpNO5grkZCNWvakZXqzPxSTMrRCky0f9EoW4S8NQw3nybZhdJSmQdPUYqKygkQDoMs7qxN5a1VHWm3q4k4FNXNIGcx7iPCcbrCEge2d4CD6fJvvMLMAqlx5AYhMtrLxSgPwTWtnrUM6Oa+5YQMTx3qWMrrapDp4FccvypzGt6HgyOr3Ggu1Tq5KAyqrh2RBDmAf/xyd+eZiEMO+dGhPop6dQ8RQMh/2jqz87Gj429rWCc7LJA3QmUVJwCxPbDJuIy7cI3W Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 02:29, Nico Pache wrote: > 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. 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. > > We also guard the khugepaged_pages_collapsed variable to ensure its only > incremented for khugepaged. > > Reviewed-by: Lorenzo Stoakes Probably best to drop Lorenzo's RB after bigger changes. > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 128 ++++++++++++++++++++++++++---------------------- > 1 file changed, 69 insertions(+), 59 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 64086488ca01..0058970d4579 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2417,6 +2417,70 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, unsigned long a > 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 *mmap_locked, > + unsigned int *cur_progress, 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; > + > + if (vma_is_anonymous(vma)) { > + result = collapse_scan_pmd(mm, vma, addr, mmap_locked, cur_progress, cc); > + goto end; > + } > + > + file = get_file(vma->vm_file); > + pgoff = linear_page_index(vma, addr); > + > + mmap_read_unlock(mm); > + *mmap_locked = false; > +retry: > + result = collapse_scan_file(mm, addr, file, pgoff, cur_progress, 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)) { !triggered_wb, right? > + 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) > + goto end; > + > + mmap_read_lock(mm); > + *mmap_locked = true; On all paths below, you set "*mmap_locked = false". Why even bother about setting the variable? > + if (collapse_test_exit_or_disable(mm)) { > + mmap_read_unlock(mm); > + *mmap_locked = false; > + return SCAN_ANY_PROCESS; > + } > + result = try_collapse_pte_mapped_thp(mm, addr, !cc->is_khugepaged); > + if (result == SCAN_PMD_MAPPED) > + result = SCAN_SUCCEED; > + mmap_read_unlock(mm); > + *mmap_locked = false; This might all read nicer without the goto and without the early return. /* If we have a THP in the pagecache, try to retract the pagetable. */ 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 unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result *result, > struct collapse_control *cc) > __releases(&khugepaged_mm_lock) > @@ -2489,36 +2553,9 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, enum scan_result * > VM_BUG_ON(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, > - &cur_progress, 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, > - &cur_progress, cc); > - } > - > - if (*result == SCAN_SUCCEED) > - ++khugepaged_pages_collapsed; > > + *result = collapse_single_pmd(khugepaged_scan.address, > + vma, &mmap_locked, &cur_progress, cc); > /* move to next address */ > khugepaged_scan.address += HPAGE_PMD_SIZE; > progress += cur_progress; > @@ -2819,13 +2856,12 @@ 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) { > cond_resched(); > mmap_read_lock(mm); > mmap_locked = true; > + *lock_dropped = true; Hm, is this change here required at all? Shouldn't we instead need to know from collapse_single_pmd() whether it dropped the lock? -- Cheers, David